[Index]
Monthly Global Tropical Cyclone Summary August 2001
[Summaries and Track Data] [Prepared by Gary Padgett]
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Cyclones
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Monthly Global Tropical Cyclone Summary August 2001 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
AUGUST, 2001
(For general comments about the nature of these summaries, as well as
information on how to download the tabular cyclone track files, see
the Author's Note at the end of this summary.)
SPECIAL NOTE: Tony Cristaldi of the NWS office in Melbourne, Florida,
rather inadvertently "discovered" a hitherto unreported tropical (or
possibly subtropical) cyclone which occurred in the Southwest Indian
Ocean in April. According to Philippe Caroff of the La Reunion TCWC,
this system formed to the south of Reunion's AOR; therefore, no
warnings were issued on the cyclone. This system is being researched
and hopefully more information and a track will be forthcoming in a
couple of months.
***********************************************************************
AUGUST HIGHLIGHTS
--> Western North Pacific very active, but no typhoon landfalls
--> Three tropical storms in the Atlantic fall just short of reaching
hurricane intensity
***********************************************************************
***** Feature of the Month for August *****
RESULTS OF TROPICAL CYCLONE SURVEY - PART 4
MONSOON DEPRESSIONS
As promised I am trying to wrap up reporting on the responses to my
tropical cyclone survey that I sent out last March. I have covered
the topics of cyclone size as a possible classification criteria (May
Feature), classification of subtropical/hybrid cyclones (June Feature),
and warning strategies for subtropical/hybrid cyclones (July Feature).
This month I will summarize the few opinions I received on the subject
of monsoon depressions. Exactly what is a monsoon depression? The
definition of a monsoon depression which used to be given in the Annual
Tropical Cyclone Report published by JTWC reads as follows:
"A monsoon depression is a tropical cyclonic vortex characterized
by (1) its large size, the outer-most closed isobar may have a
diameter on the order of 600 nm; (2) a loosely-organized cluster
of deep convective elements; (3) a low-level wind distribution which
features a 100 nm diameter light-wind core which may be partially
surrounded by a band of gales; and (4) a lack of a distinct cloud
system center."
Monsoon depressions do not occur in all tropical cyclone basins.
They are extremely rare in the Atlantic basin: one occurred in the
western Caribbean in May, 1986, and Tropical Storm Frances of 1998
in its earlier stages had the appearance of a monsoon depression.
The main regions where they seem to develop most frequently are the
North Indian Ocean, the tropical Northwest Pacific basin, the vicinity
of northern Australia and occasionally the South Pacific. Philippe
Caroff of the La Reunion TCWC indicates that they are very rare in
the Southwest Indian Ocean. Jack Beven years ago related to me that
an occasional Eastern Pacific tropical cyclone seemed to have monsoon
depression characteristics. Mark Lander has told me that on
infrequent occasions monsoon depressions will form in the austral
autumn over Africa south of the equator and sometimes move westward
over the South Atlantic. Such a system may have been responsible for
the development of the only known South Atlantic tropical cyclone to
date--a strong tropical depression or perhaps minimal tropical storm
in April, 1991. Some of the stronger African waves which move out
into the Cape Verde region also occasionally display some monsoon
depression features.
Since classic monsoon depressions are an extremely rare feature in
the Atlantic basin, the NHC forecasters who responded to my survey
didn't have all that much to say. James Franklin indicated that he
would probably treat a monsoon depression (with gales) as a non-
tropical gale center. Jack Beven posed the question "how small does
the core of a cyclone have to become for the system to be considered
tropical? From a theoretical standpoint the threshold would be when
the tropical cyclone energetics become predominant. From a practical
standpoint, I don't know the right criteria or data to make such a
determination objectively."
Philippe Caroff, in response to the question about spatial
distribution of gales within a circulation, indicated that for a system
in which gales are well-removed from the center (such as in a monsoon
depression), he felt that such gales should fairly well encompass the
center before the system was named as a tropical storm. Matthew Saxby
of Australia is in favor of naming monsoon depressions with gale-force
winds as tropical cyclones because their greater size would likely make
them more damaging.
David Roth of HPC writes, "I know monsoon depressions can mock
subtropical cyclones when it comes to maximum winds being well-removed
from the center. Any radius should work, as long as the winds are
caused by some direct effect of the existence of the LOW, like
increased pressure gradient, and the system is deeply warm-core (to
at least 500 mb)." In his reply to the question about spatial
distribution of gale-force winds as a criteria for classification as
a tropical cyclone, Rich Henning wrote, "I personally don't think
there should be a minimum for all the quadrants. If there are 50-kt
winds in the northeast quadrant of a monsoon-type cyclone, and only
15 kts in the southwest quadrant...it is still a tropical cyclone."
Although Mark Lander did not respond to my survey, I know from past
correspondence and postings from Mark that he does consider monsoon
depressions which have developed bands of gales within the circulation
to be bonafide tropical cyclones worthy of having warnings issued.
In a letter posted to some discussion lists in September, 1998, after
the development of Tropical Storm Frances in the Gulf of Mexico, Mark
pointed out that in the Northwest Pacific basin, monsoon depressions
are the systems which are the precursors of most of the typhoons,
especially those originating in the deep tropics. Most monsoon systems
which achieve winds of 30 kts go on to become "conventional tropical
cyclones" (i.e., with organized central convection and tighter
gradients). Winds can increase in these systems to 50 kts in some
portions before persistent central convection is established. To
quote Dr. Lander, "Attempts to say that this is due to the gradient
between the LOW and some high pressure area, or any other line of
reasoning to avoid calling it a tropical storm, are misleading, and
a danger lurks. As soon as persistent central convection develops,
one has instantly a large, full-fledged 'conventional' tropical storm
(or even near hurricane or typhoon), and has to suddenly go to a
tropical cyclone warning with an embarrassingly high initial
intensity."
Mark also wrote that "the JTWC has for years had trouble with these
systems. People say they are not tropical cyclones; that they are
hybrid systems of some sort; that they are not warm core--the
explanations are legion. Most of the time the effort goes into
explaning why a tropical cyclone warning should not be issued on such
systems. Part of the problem is the Dvorak tropical cyclone
classification system. Largely developed from Atlantic tropical
cyclones, Dvorak defines four basic patterns of (for lack of a better
word) 'conventional tropical cyclones': (1) shear pattern, (2) curved-
band pattern, (3) CDO pattern, and (4) eye pattern. Monsoon
depressions do not fit neatly into this scheme and are not common in
the Atlantic. Thus, Dvorak's techniques do not address them."
In closing I'll include the reply I received from Julian Heming of
the UK Meteorological Office. Julian's reply didn't address the
specific questions I'd raised, but rather shed light on the impact
of the issuance or non-issuance of warnings on the performance of
numerical models. Julian wrote:
"I've seen various views aired on this subject in the past and I
probably haven't got too much to add to those who are more at the
'cutting edge' of tropical cyclone warning strategies. However, from
the (UK) Met. Office's point of view, the most important thing is to
have good information to use in initialising cyclones (be they
tropical, subtropical, midgets, etc) in our model. For us that means
receipt of a warning or advisory from the relevant tropical cyclone
warning centre. If a warning centre decides not to name a cyclone and
does not issue a warning because it is not a 'classical tropical
cyclone', then our model (and I presume other models which use
advisories in their initialisation procedures) will not have the
benefit of information produced by tropical analysts. This could
possibly result in an inferior model forecast. Of course, if a cyclone
is too far removed from being a true tropical cyclone, then it may not
be appropriate to use some initialisation techniques, but I think on
most occasions having some information to feed the model is better
than none at all. I'm sure there will be arguments made for not
issuing warnings until a cyclone is truly tropical, but I thought I'd
present the viewpoint from one involved in model initialisation of
tropical cyclones."
I'd like to thank everyone who took the time to respond to my
survey, and I hope that these ideas and opinions I've presented will,
in a small way, lead to further discussions among tropical cyclone
forecasters and researchers with the goal in mind of trying to forge
a more globally consistent set of classification criteria and warning
strategies for these various types of marginal tropical cyclones.
***********************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for August: 3 tropical storms
NOTE: Much of the information presented below was obtained from the
TPC/NHC discussion bulletins issued with every regular advisory. All
references to sustained winds imply a 1-min averaging period unless
otherwise noted. Some information was also obtained from the monthly
summary for August prepared by the Hurricane Specialists and available
on TPC/NHC's website.
Atlantic Tropical Activity for August
-------------------------------------
Following Tropical Storm Allison in early June, the Atlantic basin
remained quiet save for one short-lived minor tropical depression in
July. The tropical cyclone season, however, began to get underway in
earnest early in August with the development of Tropical Storm Barry
in the eastern Gulf of Mexico. Barry made landfall in the Panhandle
of Northwestern Florida during the night of 5-6 August just shy of
hurricane intensity. Tropical Storm Chantal developed on 16 August
east of the Windward Islands. The storm was moving so rapidly it lost
its circulation and was downgraded to a tropical wave later that day.
The next day it regained its circulation and was re-upgraded to a
tropical storm in the central Caribbean. Chantal moved westward and
eventually made landfall near Chetumal, Mexico, around 0000 UTC on
21 August as a strong tropical storm.
Tropical Storm Dean developed rather suddenly just north of the
Virgin Islands on 22 August. However, the storm encountered a hostile
shearing environment and weakened to a tropical wave the next day.
Some of the convection associated with Dean moved northward, interacted
with a non-tropical LOW, and eventually redeveloped into a tropical
cyclone south of the Canadian Maritimes. During its second incarnation
Dean almost became a hurricane before encountering cooler waters and
increased shear in the North Atlantic.
Three named storms is about normal for August, but the lack of a
hurricane is somewhat unusual--the average (1950-2000) is 1.55. The
last August which didn't produce a hurricane was in 1997--there were
no tropical storms or depressions either. The disintegration of two
named storms back to tropical waves followed by their subsequent
redevelopment to tropical storm intensity was also unusual. This
trend, strangely, continued into September as both Tropical Storm Erin
and Tropical Depression 07 (pre-Felix) were downgraded to tropical
waves but subsequently regained their circulations and went on to
become major hurricanes.
Tropical Storm Barry (TC-03)
2 - 7 August
-----------------------------
A. Origins
----------
Barry was the first tropical storm of the 2001 season to form from
an African tropical wave, but that development didn't occur until the
system had reached the southeastern Gulf of Mexico. The parent wave
was located in the eastern Atlantic south of the Cape Verdes on 25 July
and was moving rapidly westward. By the 26th the disturbance was
located around 1400 nm east of the Windward Islands. Atmospheric
conditions were not favorable for intensification and there was little
associated convection. The wave entered the eastern Caribbean area on
29 July. The convection was not well-organized but pressures had
fallen a bit and the system was producing showers, thunderstorms, and
gusty winds over portions of the Lesser Antilles. The tropical wave
continued westward across the Caribbean--on the 31st it was generating
showers and thunderstorms from the central Caribbean northward across
Hispaniola into the southeastern Bahamas; however, there were still no
signs of increasing organization.
Early on 1 August scattered showers and a few thunderstorms extended
from the northwestern Caribbean northeastward across Jamaica, eastern
Cuba, and into the Bahamas and were forecast to spread across western
Cuba and southern Florida later in the day. The TWO noted that some
slow development was possible over the next day or two. During the
afternoon satellite imagery and surface observations indicated that
the convection was becoming better organized near Dry Tortugas Island
in the southeastern Gulf of Mexico. The weak surface LOW changed
little in organization during the night; it was interacting with a
small upper-level LOW and upper-level winds were not favorable for
rapid intensification. Most models, however, suggested that tropical
cyclogenesis would occur, and during the morning of the 2nd the LOW
began to show signs of intensification. TPC/NHC issued a Special
Tropical Disturbance Statement at 1330 UTC which stated that surface
observations and visible satellite imagery were indicating that a
tropical depression might be forming. An Air Force reconnaissance
place reached the area around midday and found 48-53 kt winds at
300 m, so the LOW was upgraded directly to Tropical Storm Barry in
a special advisory at 1900 UTC. Barry, which was then located about
270 nm south-southeast of Fort Walton Beach, Florida, was more of a
hybrid storm at that point than a purely tropical system as it was
still sort of tangled up with the upper-level LOW.
B. Track and Intensity History
------------------------------
After being upgraded to a tropical storm, Barry strengthened
to 40 kts as it moved slowly west-northwestward. Late on the 3rd the
storm slowed to an erratic drift a couple hundred miles south of the
western Florida Panhandle, remaining in this general area until early
on the 5th, when it began a steady northward march toward the coast.
Barry had weakened to a minimal tropical storm by 0600 UTC on 3 August,
and operationally remained at that intensity for 48 hours. However,
reconnaissance flights during the night of 3-4 August and on the 4th
could find no tropical storm-force winds. The Monthly Summary for
August prepared by the staff of NHC indicates that Barry weakened to
a depression on 3 August, and it seems likely that will be reflected
in the final storm report and Best Track. Since the pressure remained
steady during this period and the circulation of Barry was large and
well-defined, it was maintained as a minimal tropical storm in real
time, although a couple of NHC discussions indicated that Barry very
possibly was only a tropical depression.
Barry began to show signs of re-intensification during the evening
of the 4th as very deep convection with cold cloud tops reaching -81 C
at times blossomed near the LLCC. A reconnaissance flight around
1200 UTC on 6 August found that the pressure had fallen 14 mb in six
hours to 990 mb. A special advisory was issued at 1300 UTC to post
hurricane warnings from Pascagoula, Mississippi, eastward to the
Ochlockonee River in northwest Florida. Tropical storm warnings were
already in place for portions of the coast, and these were extended
eastward to the mouth of the Suwanee River. Tropical Storm Barry
reached its peak intensity of 60 kts around this time, but the
intensification trend leveled off and the storm remained at just under
hurricane intensity until landfall early on the 6th.
Barry's center made landfall around the middle of the night of
5-6 August about 30 km east of Fort Walton Beach between the Walton
County communities of Miramar Beach and Grayton Beach. The weakening
cyclone continued inland across the Panhandle, moving just east of
Crestview, and northward into southern Alabama, passing over or very
near the author's home near Andalusia. Barry turned to a northwestward
track as it marched inland and had weakened to a tropical depression
over southwestern Alabama by 1500 UTC on the 6th. The remnant LOW
speeded up somewhat for a time after landfall and had reached the
Alabama-Mississippi border near Aliceville, Alabama, by 2100 UTC.
HPC had assumed responsibility for issuing storm summaries after Barry
was dropped by NHC, and the fourth and final HPC summary, issued at
1500 UTC on 7 August, indicated that the weak remnants of Barry were
located near Memphis, Tennessee. They were last seen over south-
eastern Missouri on the 8th.
C. Meteorological Aspects
-------------------------
Barry was upgraded to a tropical storm at 1900 UTC on 2 August. By
2100 UTC convection had wrapped more than halfway around the LLCC and
outflow was good in the eastern semicircle. A reconnaissance plane
found 54-kt winds at 300 m and a pressure of 1008 mb. Some south-
westerly vertical shearing was hampering Barry at this time. The
NHC discussion issued at 03/0300 UTC, written by Jack Beven, provides
a good example of some of the difficulties encountered in following
tropical cyclones even with multiple observational platforms available.
Reconnaissance fixes indicated that the center was moving west or west-
northwest at about 10 kts. However, satellite fixes, including some
good visible pictures, suggested the center was moving north or even
east of north. Furthermore, data from Buoy 42003 supported the
aircraft fixes while the Tampa WSR-88D radar supported the satellite
positions! The best conclusion seems to be that the center was tilted
due to the southwesterly shear and that satellite and radar were
tracking the upper-level center.
Early on the 3rd, strong upper-level westerlies became established
over Barry and the LLCC became detached from the limited convection.
Later during the morning some convective organization was regained,
and a reconnaissance flight found 35-40 kt winds and a pressure of
1007 mb. The westerly shear continued to decrease during the afternoon
and Barry's appearance continued to improve. However, no sooner had
Barry begun to recover from the westerly shear when it was hit by
strong northeasterly flow associated with a cyclonic shear axis which
had moved over the storm. Barry likely weakened to a tropical
depression during the night of 3-4 August--a couple of reconnaissance
flights could find no winds of tropical storm intensity. However, the
pressure had dropped to 1005 mb and satellite intensity estimates from
TAFB and AFWA were 35 kts, so the cyclone was maintained as a minimal
tropical storm. A flight during the morning of the 4th reported a
pressure of 1006 mb and winds to 39 kts south of the center.
During the evening of 4 August another reconnaissance mission found
flight-level winds of 44 kts and a minimum pressure of 1003 mb. The
storm was slowly improving in organization, and during the early
morning hours of the 5th, Barry developed some very deep convection
with cold cloud tops to -81 C at times near the LLCC. The center was
not embedded in the deepest convection but rather was on the north-
western edge due to some west-northwesterly shear which had developed
ahead of a shortwave trough that was digging down over Arkansas and
Louisiana. The MSW was increased to 40 kts at 0900 UTC based on TAFB
and SAB estimates of T3.0. A reconnaissance flight around 1200 UTC
found that the pressure had fallen 14 mb to 990 mb in a six-hour
period. Winds were upped to 50 kts and the hurricane warnings were
ordered for portions of the Gulf Coast. This rapid intensification,
however, did not continue throughout the day. The structure of Barry
had been changing with the development of outer banding features in the
eastern semicircle which seems to have isolated the inner core and
slowed the intensification process. Also, the westerly shear over the
storm had likely brought some drier air into the inner core. Barry did
not weaken, however, as a dropsonde released at 1900 UTC reported
surface winds of 61 kts.
During the night of 5-6 August, WSR-88D radar observations showed
transient eyewall formations, but the inner core never became better
defined with the eyewall remaining open over the southern semicircle.
A reconnaissance flight at 06/0451 UTC found a 700-mb flight-level
wind of 71 kts southeast of the center and an extrapolated minimum
pressure of 990 mb. The last dropsonde into the storm, at 0335 UTC,
with the center still about 17 nm offshore, had reported a SLP of
993 mb. After Barry's center had made landfall and crossed over
Choctawhatchee Bay, it passed near Eglin AFB range station C-52
(30.6N, 86.3W) where the altimeter reached a minimum of 994.2 mb at
0547 UTC with southeasterly winds of 25 kts, gusting to 37 kts. The
strongest gust was 52 kts from the northeast at 0516 UTC. The
peak gust reported at the Eglin Main weather station (around 15 km to
the west-southwest) was 270/55 kts at 0627 UTC; the sustained wind at
the time was 33 kts. Destin, Florida, reported a gust of 37 kts
around midnight when Barry's center was about 17 nm east-southeast
of that location and the northern eyewall had already moved onshore.
Cape San Blas, well to the east, reported a peak gust of 36 kts.
Tyndall AFB near Panama City recorded 186 mm of rainfall in the
24 hours ending at 06/1200 UTC with another 8 mm falling during the
next six hours. Eglin AFB had recorded 94 mm by 1400 UTC on the 6th.
The first storm summary issued by HPC included some 5-day rainfall
totals for Barry ending at 06/1200 UTC. Many locations in the southern
portion of the state experienced heavy rainfall associated with the
tropical wave which spawned Barry and during the storm's early
formative stages. Tynfall AFB's 5-day total was 220 mm followed by
204 mm at the West Palm Beach International Airport. Fort Lauderdale
recorded 202 mm during the 5-day period. Quite a few locations over
the state had totals between 150 and 175 mm. Tallahassee recorded
156 mm for a 5-day total ending at 1800 UTC--for the 12-hour period
06/1200 UTC through 07/0000 UTC that site picked up 109 mm. During
the 30 hours ending at 1800 UTC on 6 August, Apalachicola measured
156 mm. The highest 3-day storm total, ending at 07/1200 UTC, was
226 mm at Tallahassee.
Rainfall amounts tapered off considerably as Barry weakened and
moved across Alabama. Maxwell AFB near Montgomery recorded a 24-hour
total of 70 mm, ending at 07/1200 UTC, while the Shelby County Airport
picked up 59 mm for the same period. Some storm totals in Alabama for
the 72-hour period ending at 07/1200 UTC include 103 mm at Troy, 89 mm
at Ozark, and 82 mm at Maxwell AFB. Valdosta, Georgia, well-removed
from Barry's track, recorded 61 mm for the same period while Tupelo,
Mississippi, measured 27 mm for a 3-day total.
D. Damage and Casualties
------------------------
Winds and rain associated with Tropical Storm Barry caused minor
damage in the Florida Panhandle amounting to about $30 million. No
deaths were attributed to the storm.
Tropical Storm Chantal (TC-04)
15 - 22 August
-------------------------------
A. Origins
----------
Tropical Storm Chantal was one of the oddest and most troublesome
Atlantic tropical cyclones in recent years. It was the first of four
consecutive "interrupted" cyclones--systems whose centers dissipated
only to regenerate later. Chantal was also one of the most rapid
movers on record for the deep tropics, racing across the tropical
Atlantic and central Caribbean at speeds of up to 25 kts at times.
This rapid motion resulted in Chantal's having a great difficulty main-
taining a well-defined closed circulation even after it regenerated
in the southeastern Caribbean. It's not far from the truth to say
that Chantal was almost an open wave with winds to near hurricane
force--something which "just isn't supposed to happen". Like Barry
before it, Chantal did slow down and become better organized and was
near hurricane intensity when it made landfall near Chetumal, Mexico.
A tropical wave left the west coast of Africa around 12 August,
producing a large area of showers and thunderstorms but not very well
organized. By the next day there had been a slight increase in
convective organization and a TWO indicated that the system had some
potential for slow development over the next couple of days. Early on
the 14th the wave was even better organized, and was accompanied by a
broad area of low pressure but still lacked persistent central
convection. By 1500 UTC on 15 August the wave had acquired enough
organized convection that it was upgraded to Tropical Depression 04,
located about 900 nm east of Barbados. The center was poorly-defined
and appeared to be located east of the main convection, but since low
shear and warm waters were ahead of the depression, intensification
was forecast. A strong mid-level ridge to the north was steering
TD-04 westward at 20 kts or more.
By the early morning of 16 August, TAFB was estimating 35 kts (the
other agencies were lower), and the depression appeared to be very near
tropical storm strength. The NHC specialist on duty opted to wait
until visible satellite pictures were available before upgrading in
order to get a better handle on the center location. The depression
was moving westward at about 24 kts at the time. An intermediate
advisory was issued at 1200 UTC, upgrading the system to Tropical Storm
Chantal, located about 325 nm east of Barbados.
B. Track and Intensity History
------------------------------
The cloud pattern of Chantal had improved since the previous day
with banding features and excellent outflow due to an upper-level anti-
cyclone located over the tropical cyclone. However, there was a very
big surprise when the first Hurricane Hunters' reconnaissance mission
reached Chantal during the early afternoon. The crew was not able to
locate any closed circulation at the surface. Chantal exhibited the
cloud pattern of a fairly well-defined tropical cyclone, but the rapid
translational speed had led to the storm's being unable to maintain its
surface circulation--if it had ever existed at all. The NHC Monthly
Summary suggests that possibly Chantal was not a bonafide tropical
storm on 16 August. It will be interesting to see how this phase of
Chantal's life is handled when the final storm report becomes available
later. A special advisory was issued at 07/0000 UTC downgrading
Chantal to a tropical wave about 100 nm west of Barbados.
Even as a tropical wave, the system produced winds to tropical storm
force on Martinique as it passed through the Windward Island chain.
By the morning of the 17th convection had greatly increased and the
system exhibited a very impressive cloud pattern. After looking very
hard, a reconnaissance plane found a small 1010-mb center about
330 nm south-southeast of San Juan, Puerto Rico, so advisories were
commenced once more on Chantal at 1500 UTC. The depression was still
moving rapidly westward at 23 kts; nonetheless, another flight during
the afternoon found a well-defined center with a pressure of 1006 mb
and winds strong enough to justify upgrading the system back to
tropical storm status, so Chantal became a tropical storm once more
at 2100 UTC with 35-kt winds, located about 250 nm south of San Juan.
Based on reconnaissance reports during the night, by the morning of
18 August Chantal's MSW had been increased to 50 kts, but the 1500 UTC
advisory noted that satellite imagery revealed an exposed LLCC moving
rapidly to the west-northwest, leaving the mid-level circulation and
most of the convection behind. Reconnaissance planes, however, had
found winds exceeding hurricane force at flight level (450 m), so in
spite of the very disorganized appearance, Chantal continued to
maintain rather strong winds and even intensified some. By 1200 UTC on
19 August, the storm had reached an initial peak intensity of 60 kts at
a point about 215 nm southwest of Kingston, Jamaica, even though all
the strong winds were in the northeastern quadrant. To the south of
the broad and ill-defined center only light and variable winds were
found. (More on this particular reconnaissance flight below.)
Chantal's forward motion slowed some on the 19th and 20th, but the
benefits of the slower translational speed were offset by some shear
from an upper-level trough over the western Caribbean. The storm
struggled to survive as a tropical cyclone, but the intense convection
helped to maintain fairly strong winds and the MSW was never lowered
below 55 kts during this period. As Chantal approached the Yucatan
Peninsula on 20 August, the shear began to relax and the storm
responded by developing a better-defined center and intensifying right
up to the moment of landfall. The MSW was estimated at 60 kts once
again as the center made landfall near Chetumal, Mexico. The 21/1500
UTC discussion noted that even though the center of Chantal had been
over land for around 12 hours, the satellite signature was the best
that it had been during the storm's history.
Chantal was originally forecast to move west-northwestward across
the Yucatan Peninsula and emerge into the Bay of Campeche with a chance
of re-intensifying. However, by 2100 UTC on the 21st convection had
decreased significantly and most of what was left was over the
Caribbean well removed from the center. Chantal was downgraded to a
30-kt depression; the system, however, was still showing anticyclonic
outflow. By 22/0300 UTC convection had continued to diminish and
the mid-level center had sheared off to the northeast. Even though
a reconnaissance flight found 25-35 kt winds at flight level over the
Bay of Campeche to the north, the low-level center turned to the south-
west and began to dissipate over southeastern Mexico. The final
advisory on Tropical Depression Chantal, at 22/1200 UTC, placed the
dissipating center near Villahermosa, Mexico.
C. Meteorological Aspects
-------------------------
Reconnaissance flights into Chantal on 18 and 19 August reported
some unusual happenings. A flight during the evening of the 17th
reported 58-kt winds at 450 m north of the center with a central
pressure of 1004 mb. Convection was more concentrated but the crew
reported that the circulation at flight level was not well-defined. A
reconnaissance mission around 18/0600 UTC reported winds to 73 kts at
450 m, but this was adjudged to likely be due to mesoscale convective
effects. During the morning of the 18th satellite imagery revealed an
exposed LLCC moving rapidly west-northwestward away from the mid-level
circulation and convection; nonetheless, a reconnaissance plane fixed
another weak center to the south with flight-level winds of 67 kts.
Chantal had become disorganized with an elongated center. During the
afternoon it became apparent that unexpected shear from an upper-level
trough over the western Caribbean was the culprit that was disrupting
Chantal's cloud pattern, which consisted of a very tight center of
low clouds to the west of a strongly-curved band of deep convection.
Reconnaissance data during the afternoon showed a pressure of 1003 mb
and 50-60 kt winds in the band of convection.
The most unusual reconnaissance missions occurred early on the
morning of 19 August. The flight around 0600 UTC reported 62-kt winds
at 450 m in the southeast quadrant with the pressure down to 997 mb--
a drop of 6 mb since the previous mission. Satellite intensity
estimates were running around 45-55 kts, but the center was fixed on
the western edge of the deep convection, whereas the reconnaissance
crew placed the center farther back into the deep convection. Thus,
it appeared that Chantal's forward motion had slowed dramatically and
that the storm was forming an eye and possibly embarking on a spell
of rapid intensification.
The 1200 UTC reconnaissance was most extraordinary. Rich Henning
was present on that flight and has personally related to me some of
the surprises they found. They flew into Chantal expecting to find a
hurricane but barely found a closed circulation. Because of some deep
convection with very intense lightning and likely strong updrafts and
downdrafts, the aircraft entered the storm at a higher altitude (around
1500 m) than the earlier flights. The plane approached the center
from the northeast and 82-kt winds were observed in that quadrant.
However, no eye was found, and they eventually broke out of the
convection into a large, broad area of light and variable winds well
southwest of the main area of deep convection. The lowest pressure
found was 1004 mb. Rich stated that it was with great difficulty that
they found enough of a circulation to justify a vortex fix. Only very
light and variable winds could be found to the south of the broad
center. Two subsequent flights through the northeast quadrant found
peak winds of 72 kts and 62 kts, respectively. What seems to have
happened was that during the night Chantal had made an attempt at
forming a tight vortex, but that it failed to develop further and the
storm was weakening by the time the 1200 UTC mission reached the area.
Chantal remained in a disorganized state until the morning of the
20th when it began to show somewhat better organization. A flight
into the storm around 0000 UTC found the storm still poorly-organized
with the LLCC about 100 nm to the west of the nearest deep convection.
The reconnaissance crew reported flight-level winds of 69 kts, but the
dropsonde released at that point measured surface winds of only 38 kts.
Chantal was not effectively transporting momentum to the surface.
Reconnaissance fixes were consistently to the south of the low-level
cloud swirl, which implied that the surface wind center lay to the
south of the low-level vorticity center. The next reconnaissance
mission into the storm at 0532 UTC found a better-defined circulation,
and satellite imagery indicated that a large thunderstorm cluster had
developed over or near the LLCC. The peak flight-level winds found
were 61 kts at 850 mb at 0552 UTC. By afternoon Chantal's appearance
was still better--satellite imagery portrayed a comma-shaped cloud
pattern with the center near the edge of the dense overcast, the
southern portion of the circulation had become distinct, the strongest
winds in the northeast quadrant were nearer the center, and water vapor
loops suggested that the shear was decreasing.
Reports from USAF reconnaissance flights and a NOAA P-3 research
mission revealed that Chantal continued to strengthen right up to the
time of landfall near Chetumal. A dropsonde in deep convection north-
east of the center at 20/2144 UTC measured 58-kt winds at the surface
and the peak flight-level wind was 71 kts--these values corresponding
to a surface MSW of 60 kts. Right at landfall there was a burst of
deep convection very close to the center. The NHC advisory at 0900
UTC stated that surface observations from Chetumal and Belize, along
with radar reports, indicated that Chantal had either stalled or had
developed a new center farther south and east of the previous advisory
position. Radar data at 0800 UTC indicated that an eyewall was trying
to close off between San Pedro and Corozal. As noted earlier,
Chantal's satellite signature continued to improve for a while after
the center had moved inland.
D. Damage and Casualties
------------------------
No fatalities were associated with Chantal while it was a tropical
cyclone, although two deaths were reported in Trinidad due to lightning
associated with the passage of the tropical wave through the Lesser
Antilles. Damage in Belize was estimated at $10-15 million, and there
were no reports of significant damage in Mexico.
Tropical Storm Dean (TC-05)
22 - 29 August
----------------------------
A. Origins
----------
Unlike its two predecessors, Dean's formation doesn't seem to be
directly related to a wave of African origin. Based upon information
taken from TPC's Tropical Weather Discussions, the progenitor of Dean
seems to be a disturbance initially located on the ITCZ that detached
itself and headed west-northwestward. The disturbance was first
mentioned at 1800 UTC on 18 August when located near 13.0N, 35.0W,
with an associated 1015-mb LOW. By the early morning of the 19th the
wave was located about 1400 nm east of the Windward Islands. It was
not too well-organized but was showing signs of increased convective
organization. On the 20th the disturbance had moved to a position
about 650 nm east of the Windwards and shower activity was still
limited.
Convection increased on the 21st when the wave was located about
450 nm east of the Lesser Antilles. A TWO noted that upper-level
winds were not favorable for rapid development but some slow
organization was possible. A reconnaissance flight by the Hurricane
Hunters during the afternoon of 21 August was unable to locate a
closed LLCC. The wave was moving rather rapidly west-northwestward
at 20 kts; it was well-organized but upper-level winds were inhibiting
development. On the morning of the 22nd the wave appeared much better
organized based on surface, radar and satellite observations. The
system was moving west-northwestward at 18-22 kts through the northern
Lesser Antilles and upper-level winds were becoming a little more
favorable for strengthening.
The next reconnaissance mission into the disturbance on the after-
noon of 22 August found a surprise--a small 1010-mb center located
north of the Virgin Islands with 65-kt winds at 300 m over the north-
east quadrant. Therefore, advisories were initiated immediately on
Tropical Storm Dean with 50-kt winds. Dean's center was located at
the time about 115 nm east-southeast of San Juan and moving west-
northwestward at 22 kts. The center was exposed on the western edge
of the deep convection, and the NHC discussion noted that some of the
observed strong winds were likely due to the rapid translational
speed. On the last pass of the reconnaissance plane through the
storm, a 1009-mb center was fixed and maximum flight-level winds were
63 kts. The center was exposed at the northern end of a convective
band trailing southward across the Virgin Islands.
B. Track and Intensity History
------------------------------
Exactly what factors led to the sudden intensification of the
tropical wave into a fairly strong tropical storm aren't clear, but
the intensification trend certainly did not continue. The 23/0300
UTC advisory noted that a recent QuikScat pass had showed an open
wave, leading to the possibility that Dean no longer possessed a
closed circulation. The small storm had moved into a region of
fairly strong vertical shear and found it to be more than it could
withstand. Nighttime infrared imagery suggested the possibility of
multiple circulation centers, and a reconnaissance flight during the
morning of the 23rd was unable to locate a closed surface circulation.
The plane found a minimum pressure of 1013-1014 mb with maximum
flight-level winds of 42 kts east of the remnant low-cloud swirl. So
a final advisory on Dean was issued at 1500 UTC placing the
dissipating center about 325 nm northwest of San Juan.
The remains of former Tropical Storm Dean moved northward ahead
of a slow-moving frontal boundary lurking off the U.S. East Coast.
By the morning of the 24th satellite images indicated that Dean's
remnants had become better organized with a possible broad surface
circulation forming about 350 nm west-southwest of Bermuda. A
reconnaissance mission into the disturbance during the afternoon
found a broad 1011-mb LOW with a weak wind field about 300 nm west-
southwest of Bermuda, moving north-northeastward at around 13-18 kts.
The weak LOW interacted with a non-tropical trough to its west, and by
1200 UTC on the 25th the two systems had merged to form a hybrid
depression roughly 150 nm northwest of Bermuda.
During the 26th ships began to report gale-force winds and
convection slowly increased around the center. Early on 27 August
a ship with call sign WGMJ reported southerly winds of 55 kts with
a SLP of 1004 mb near the center of the cloud mass. Since the
system had intensified and taken on a more tropical appearance once
more, advisories were re-initiated on Tropical Storm Dean at 27/0900
UTC. The storm was centered at 0600 UTC about 425 nm south-southeast
of Halifax, Nova Scotia, and was moving northeastward at 16 kts.
The cyclone subsequently attempted to form a banding eye, and the
MSW was increased to 60 kts at 1800 UTC when Dean was centered about
475 nm southwest of Cape Race, Newfoundland. Convection began to
decrease early on the 28th with the center defined by a swirl of low-
to mid-level clouds east of the primary convection. At 0500 UTC a
Canadian buoy (44141) reported a pressure of 1004.3 mb and 5.5 m seas
55 nm southeast of the center.
As Dean began to move over colder SSTs of 22 C or less, cool and
dry air began to work into the system, the pressure fields began to
broaden, and the storm began to rapidly weaken and lose tropical
characteristics. The final NHC advisory was issued at 1500 UTC on
the 28th and placed Dean about 200 nm south of Cape Race. The storm
was fast becoming extratropical as it accelerated to the east-
northeast. David Roth considers the system to have re-assumed a sort
of hybrid/subtropical appearance for a day or so as there was limited
convection southwest and north of the center. Transition to an
extratropical cyclone was complete by 30/0000 UTC as all convection
had disappeared and the system had become linked to a baroclinic band
as seen in satellite imagery. The final position in David's track
places the extratropical gale over 500 nm east-northeast of Cape Race.
C. Meteorological Aspects
-------------------------
Since Dean had such a short life as a tropical cyclone, including
both phases, all the information received by the author from surface
observations and reconnaissance missions has been incorporated into
the above paragraphs detailing the storm's track and history.
D. Damage and Casualties
------------------------
Winds to tropical storm force were reported in the U. S. Virgin
Islands, and there was some damage due to flooding in Puerto Rico.
Total damage is estimated at about $2 million. No deaths were
attributed to Tropical Storm Dean.
***********************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for August: 1 tropical depression
1 hurricane
NOTE: Much of the information presented below was obtained from the
TPC/NHC discussion bulletins issued with every regular advisory (CPHC
for locations west of 140W.) All references to sustained winds imply
a 1-min averaging period unless otherwise noted. A special thanks
to John Wallace of San Antonio, Texas, for writing the summary on
Hurricane Flossie.
Northeast Pacific Tropical Activity for August
----------------------------------------------
The month of August on the average sees about four named storms
develop in the Northeast Pacific basin. Two of these will reach
hurricane intensity with one becoming a major hurricane (Category 3+
on the Saffir/Simpson scale). August, 2001, was definitely a quieter
than normal month in this basin. Only one tropical storm developed,
Flossie, although it did become a Category 2 hurricane.
In addition to Hurricane Flossie, one short-lived tropical
depression was tracked in the Eastern Pacific during August. This
depression can be traced back to a tropical wave which left the west
African coast around 7 August. The wave made its way westward across
the Atlantic and Caribbean Sea, reaching the Eastern Pacific by the
17th. Once in the Pacific the disturbance continued moving rather
rapidly westward, and by 21 August had reached the vicinity of 132W,
or about 1300 nm east-southeast of the Hawaiian Islands, and was
showing some signs of increased organization. The next day a good
low-level circulation was evident in the low clouds with ragged deep
convection near the center, so advisories were initiated on Tropical
Depression 06E, located about 1100 nm east of the Hawaiian Islands or
about 1500 nm west-southwest of Cabo San Lucas on the tip of the Baja
California Peninsula.
However, even as the depression was upgraded it was crossing the
25 C isotherm, so little further strengthening was forecast. The weak
cyclone moved slowly north-northwestward and almost immediately ran
into some southerly shear due to an upper-level trough lying to its
west. By 1200 UTC on 23 August the depression consisted mainly of
a swirl of low clouds with a few showers to the north and northeast of
the center. Some intermittent bursts of convection were seen during
the day as the trough, which although was the source of the shear,
provided some diffluence over the system. By 24/0000 UTC the
depression was beginning to dissipate with the center becoming
elongated, resembling a shear axis. With strong shear still above
the system and 24 C waters below, regeneration was deemed unlikely.
The final advisory on TD-06E was issued at 0300 UTC and placed the
disspiating center only about 200 nm north-northwest of its point of
origin.
Hurricane Flossie (TC-07E)
26 August - 2 September
---------------------------
A. Origins
----------
The origin of Hurricane Flossie does not appear to be related to a
tropical wave, but to a tropical LOW that was first noted off the
Mexican coast on 24 August. The LOW tracked west-northwestward and
steadily organized. By 0900 UTC on 26 August, its organization had
increased enough to warrant its upgrade to Tropical Depression Seven-E
approximately 175 nm south of Cabo San Lucas. The depression tracked
roughly west-northwestward, south of a 500-mb ridge. It continued to
strengthen, and was upgraded to Tropical Storm Flossie at 2100 UTC on
the 26th, located 160 nm southwest of Cabo San Lucas.
B. Track and Intensity History
------------------------------
Flossie intensified on the 27th under increasingly favorable
conditions while its track bent more toward the west; this development
spared it from cooler SSTs to its north. Satellite data supported its
upgrade to Hurricane Flossie at 2100 UTC on 27 August about 310 nm
west-southwest of Cabo San Lucas; this made it the first Pacific
hurricane in over a month. Flossie made an unusual west-southwestward
turn upon its upgrade, as the ridge to its north moved westward with
it. On the 28th, Flossie tracked slowly southwestward, due to the
strong ridge that was then to its northwest. The hurricane briefly
became quasi-stationary late on the 28th; the ridge to its north
weakened while a cyclonic shear axis to its southwest exerted a more
northerly influence on the track. Another ridge southeast of Flossie
placed the system in a weak col; even so, a slow northwestward track
commenced late on the 28th as the northern ridge weakened. Flossie
underwent a quick burst of intensification the following day, and
peaked at 2100 UTC on 29 August some 445 nm west of Cabo San Lucas.
At this time, it had an estimated MSW of 90 kts and a 972-mb CP.
Flossie slowly weakened thereafter as it tracked over cooler SSTs.
Flossie dropped below hurricane strength on the 31st; late that day
its track turned to the north, then northwestward on the 1st as a
shortwave trough "picked up" the system. The storm weakened to a
depression at 1500 UTC on the 1st, due both to increased vertical shear
and unfavorable SSTs. The final advisory on Tropical Depression
Flossie was issued at 0300 UTC on 2 September, placing the dissipating
center about 585 nm west-northwest of Cabo San Lucas, or roughly
200 nm west-southwest of Punta Eugenia. Moisture from Flossie's
remnants spread across Baja California and the American Southwest,
advected northeastward by upper-level winds.
C. Meteorological Aspects
-------------------------
Flossie was notable for both being the first storm after an
unusually long break in Northeast Pacific activity, and for being
an amazingly compact tropical cyclone. Upon its upgrade to a named
storm, tropical storm-force winds extended only 50 nm from the center;
the radii were never greater than 75 nm throughout its life. At its
peak, hurricane-force wind radii were only 15 nm, as compared to
the 15 nm-diameter of the eye itself. It has been hypothesized that
Flossie's small size was the key to its surprising peak intensity,
given its proximity to cool water and stable air; if it had been
larger, it might have entrained more dry air or caused more upwelling.
D. Damage and Casualties
------------------------
No casualties are known, and no watches or warnings were required.
***********************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for August: 3 tropical depressions **
3 tropical storms
2 typhoons
1 super typhoon
** - One of these was treated as a tropical depression only by PAGASA.
Another was classified as a tropical depression by JMA, NMCC and
Taiwan, but not by JTWC. The third was treated as a tropical
depression by JMA and briefly by JTWC; Roger Edson, however,
believes this system reached tropical storm intensity.
NOTE: Most of the information on each cyclone's history presented in
the narrative will be based upon JTWC's advisories, and references to
winds should be understood as a 1-min avg MSW unless otherwise noted.
However, in the accompanying tracking document I have made comparisons
of coordinates with JMA (Japan) and the Philippines (PAGASA) when their
positions differed from JTWC's by usually 40-50 nm or more. A special
thanks to Michael V. Padua, owner of the Typhoon 2000 website, for
sending me the PAGASA and JMA tracks.
Also, some information based upon warnings issued by the National
Meteorological Center of China (NMCC) and the Hong Kong Observatory
(HKO) is included. The tracks from these agencies were sent to me
by Huang Chunliang of Fuzhou City, China. Finally, Roger Edson of
the University of Guam sent me his versions of tracks for Tropical
Depression 15W and Tropical Depression Jolina. A special thanks to
these gentlemen for the information they sent.
In the title line for each storm I plan to reference all the cyclone
names/numbers I have available: JTWC's depression number, the
JMA-assigned name (if any), JMA's tropical storm numeric designator,
and PAGASA's name for systems forming in or passing through their area
of responsibility.
Northwest Pacific Tropical Activity for August
----------------------------------------------
A very active August followed on the heels of an active July. Six
named storms developed--one more than in July, but only three reached
typhoon intensity--one less than in July. However, one of the August
typhoons, Wutip, became the season's first super typhoon as winds
climbed to 130 kts. (All these typhoon statistics are based upon
JTWC's classifications.) None of the typhoons made landfall while
at typhoon strength, although Typhoon Man-yi passed through the
northernmost Marianas Islands. Typhoon Pabuk, after weakening to
tropical storm strength, made landfall in south-central Honshu and
skimmed eastward along the coast, passing very near Tokyo. Weak
tropical storms Usagi and Fitow made landfall in Vietnam and southern
China, respectively. Reports on all of the named cyclones follow.
There were three systems (possibly four) which were classified as
tropical depressions by one or more of the several TCWCs in the NWP
basin. Following are brief synopses of these systems.
Tropical Depression(s) of 2-3 and 6-8 August - A low-pressure area
moved quickly westward from a position several hundred miles southeast
of Okinawa. At 02/0000 UTC JMA referred to the system in their High
Seas Warning and Summary bulletin as a weak tropical depression located
about 525 nm southeast of Okinawa. By 1200 UTC the system had moved to
a position about 300 nm south-southeast of Okinawa and JMA assessed the
maximum winds to be 30 kts. The depression continued moving rapidly
westward and by 0600 UTC on 3 August was located 150 nm southeast of
Taipei, Taiwan. The system was also showing signs of weakening. It
reached the coast of China near Fuzhou City around 1500 UTC the same
day. JTWC did not classify this system as a tropical depression nor
were any TCFA's issued; however, in addition to JMA, both NMCC and
Taiwan's Central Weather Bureau treated the LOW as a depression.
After moving inland the system turned more to the north, then east-
ward after reaching Anhui Province. The depression's remnants passed
near Shanghai on 5-6 August, triggering a 14-hour period of heavy
rains which began around 1600 locally on the 5th. By 0800 (local)
the next morning, the city had averaged 150 mm of rain with the
Huangpu district netting 289 mm and several other districts, including
Xuhui and Luwan, exceeding 220 mm. The rain was reported to be the
heaviest that the Shanghai area had seen in ten years. Over 30,000
residential houses were inundated. Additionally, the system triggered
a tornado which struck Sunqiao, Shanghai.
At 0600 UTC on 6 August, JMA noted the existence of a weak tropical
depression in the southern Yellow Sea about 100 nm north-northeast of
Shanghai. JTWC also mentioned the disturbance in their STWOs, giving
it a fair potential for development. The system, however, did not
strengthen further, and after remaining quasi-stationary for a day or
so, began to move off to the northeast and crossed the Korean Peninsula
as a weak LOW. There is no conclusive evidence that this second system
was a redevelopment of the depression of 2-3 August, but it does seem
likely that they were related. (A special thanks to Huang Chunliang
for sending me the information on the Shanghai rainfall event.)
Tropical Depression Jolina - PAGASA issued bulletins on a South
China Sea system on 16-19 August which was named Jolina. During this
period the depression remained basically quasi-stationary west of
Luzon. To my knowledge no other warning centers issued any bulletins
on this system. After I had posted the August tropical cyclone
tracks, I received some information from Roger Edson on circulations
in the South China Sea. Roger wrote: "Active monsoon trough during
this period with axis around 16N. Several circulations developed
along the trough (at least one on the 13th and one on the 15th).
Finally I could follow the third circulation from the 17th (Jolina)
with good scatterometer and microwave data from this point. Nice
exposed circulation on the 21st in the mid-South China Sea." Roger
also sent his version of a track for Jolina. I have incorporated
Roger's tracking information into the track for Jolina and have
re-sent the August tracks file to the gentlemen who archive the
summaries and tracks.
Tropical Depression 15W - At 1200 UTC on 24 August, JMA noted in
a High Seas Bulletin the existence of a weak tropical depression
about 350 nm northwest of Wake Island. This system subsequently
followed a long trajectory which took it generally northwestward to
just east of the northernmost Japanese island of Hokkaido. It then
recurved to the north-northeast and passed through the southern Kuril
Islands as it became extratropical. JMA estimated that 30-kt winds
were associated with the depression on 25 August, but for the remainder
of its life it was relegated to the Summary portion of the bulletins,
implying 25-kt winds. At 1800 UTC on the 24th JTWC issued the first
of three warnings on the depression, numbering it TD-15W. The MSW
was estimated at 30 kts and the system was forecast to strengthen to
a tropical storm. However, the third warning (25/0600 UTC) indicated
that the system was merging with a frontal boundary and dissipating.
However, Roger Edson sent me his version of a track for this system
and he feels that it reached tropical storm intensity. Roger does
note that it was very difficult to follow, especially at first, as
it was very small and mostly embedded in the monsoon trough. Roger
feels that JTWC "lost" the system as it accelerated northward along
the west side of the monsoon trough, with this beginning to happen
overnight when there was no visible imagery. Roger's track for the
system follows JMA's track fairly closely and starts the depression
at 23/1800 UTC with tropical storm intensity being reached at 1200 UTC
on the 24th. Roger estimates that a peak intensity of 50 kts was
reached at 0600 UTC on 26 August when the system was located several
hundred miles east-southeast of Tokyo. It is interesting to note
that on 26 and 27 August, SAB was assigning CI numbers of 2.5 (35 kts)
which lends support to the idea that the system did reach tropical
storm intensity. In addition to the JMA/JTWC track for TD-15W, the
cyclone tracks file for August contains Roger Edson's track for this
system with several of his comments included in the remarks column.
Typhoon Man-yi (TC-12W / TY 0109)
1 - 11 August
----------------------------------
Man-yi: contributed by Hong Kong, was originally the name of a strait.
With the construction of a dam, that part of the sea has become
a reservoir.
A. Origins
----------
A STWO issued by JTWC at 0200 UTC on 31 July noted that an area of
convection was developing approximately 150 nm north of Pohnpei.
Animated infrared imagery showed persistent deep convection and
cyclonic turning whereas animated visible imagery and synoptic data did
not support the existence of a closed LLCC. A 200-mb analysis showed
weak ridging over the disturbance. A few hours later microwave
imagery depicted improving organization with weak low-level cloud lines
indicative of a developing LLCC; the development potential was upgraded
to fair.
A TCFA was issued at 0100 UTC on 1 August. Convective organization
was improving and a recent SSM/I pass had revealed a possible banding
feature south of the LLCC. The system exhibited good outflow to the
south and east. The STWO issued at 0600 UTC noted that there had been
a new flare-up of deep convection near the center during the previous
few hours. An upper-level LOW to the north was enhancing outflow, and
water vapor imagery and a 200-mb analysis depicted organizing
equatorial outflow to the south of the center. JTWC issued the first
warning on TD-12W at 01/1800 UTC with the center located about 200 nm
north-northeast of Chuuk, moving west-northwestward at 8 kts.
On the second warning--issued at 02/0000 UTC---JTWC upgraded the
depression to a tropical storm based on satellite CI estimates of 30
and 35 kts. Infrared satellite imagery depicted rapidly improving
organization and banding over the past few hours. The storm continued
moving to the northwest and steadily intensified. The MSW was upped
to 45 kts at 0600 UTC based on CI estimates of 35 and 45 kts; satellite
imagery revealed a developing 130-nm diameter CDO feature with cold
cloud tops to -83 C. NMCC upgraded the system to a tropical storm
at 0600 UTC, and JMA followed suit at 1200 UTC, naming the cyclone
Tropical Storm Man-yi. At the time, Man-yi was centered approximately
300 nm north-northwest of Chuuk or about 325 nm east-southeast of Guam.
B. Track and Intensity History
------------------------------
Initially, Tropical Storm Man-yi was steered northwestward or north-
northwestward at a fairly good clip of around 15-16 kts by a low- to
mid-level subtropical ridge to the storm's northeast. The cyclone
steadily intensified, reaching typhoon intensity at 0600 UTC on the
3rd (per JTWC) when located about 125 nm east-northeast of Saipan.
Winds had reached 95 kts by 04/0000 UTC--enhanced infrared imagery
depicted deep convection developing in the eyewall. JTWC upped the
MSW to 110 kts at 0600 UTC, noting that Man-yi was a symmetric system
with a round eye 6 nm in diameter. Typhoon Man-yi reached an initial
peak intensity of 115 kts at 1200 UTC on the 4th when satellite imagery
revealed a well-defined primary banding feature wrapping in toward the
vortex center from the southwest. Gales extended outward 145 nm
northeast of the center and 60 nm to the southwest, while storm-force
winds reached outward 75 nm to the northeast and 35 nm to the south-
west. Man-yi was centered about 200 nm southeast of Iwo Jima at the
time.
As Man-yi continued north-northwestward it moved into a weakness in
the subtropical ridge and recurved to the northeast on the 5th. The
storm reached the westernmost point of its track at 05/0000 UTC when it
was centered approximately 115 nm east of Iwo Jima. After recurving
to the northeast, Man-yi initially weakened some with winds dropping to
95 kts by 06/0000 UTC. This weakening was likely due to some shear
plus an eyewall replacement cycle. A 04/1102 UTC SSM/I pass depicted
a collapsed eyewall in the eastern quadrant with an associated banding
feature over the southwest quadrant; winds were lowered to 110 kts
at 04/1200 UTC. At 06/0000 UTC water vapor imagery indicated less
vertical shear over the typhoon with an outflow channel to the north.
Man-yi responded by re-intensifying to 115 kts by 1200 UTC on the 6th.
By this time the system had developed pronounced dual outflow channels,
and the gale- and storm-force wind radii were more symmetric than at
the earlier peak. Gales extended outward 110 nm northeast of the
center and 90 nm to the southwest, while 50-kt winds reached out an
estimated 60 nm to the northeast and 50 nm to the southwest. Man-yi's
large 45-nm round eye was centered about 250 nm northeast of Iwo Jima
at this time.
As Typhoon Man-yi continued on toward the northeast, gradually
curving back more to the north-northeast, it began to slowly weaken.
The diameter of the eye also continued to increase, reaching 65 nm
at 07/0000 UTC. The storm became one of the so-called truck-tire,
or annular, typhoons: storms which develop a very large eye in
proportion to the CDO and look like huge doughnuts or truck tires.
Winds were down to 95 kts by 1800 UTC on 7 August and the storm was
beginning to exhibit signs of extratropical transition. By the 8th
Man-yi was north of the ridge axis and still moving northeastward,
but a mid-level HIGH was forecast to move out of the Sea of Okhotsk
and cause the storm to take a more northward track. This forecast
verified--by 08/1200 UTC Man-yi was moving northward at 17 kts from
a position about 550 nm east of Tokyo. Peak winds were down to
minimal typhoon intensity and cold air was wrapping into the
circulation from the north and west with no eyewall visible any
longer.
JTWC declared Man-yi to be extratropical at 1800 UTC on the 8th and
issued their final warning, placing the storm about 500 nm south of the
Kuril Islands. JMA continued to carry Man-yi as a tropical storm until
1800 UTC on 9 August when it was well east of Hokkaido. The extra-
tropical remnants of Man-yi continued trekking northeastward parallel
to the Kuril Island chain. By 11/0000 UTC the system had weakened to a
20-kt LOW southeast of the tip of the Kamchatka Peninsula.
In summary, Typhoon Man-yi reached an estimated peak intensity (per
JTWC) of 115 kts on three occasions: at 1200 and 1800 UTC on 4 August,
at 0600 UTC on 5 August, and at 1200 and 1800 UTC on 6 August. The
minimum central pressure assigned by JMA was 945 mb at 0000 and 0600
UTC on 5 August.
C. Meteorological Aspects
-------------------------
The most noteworthy event of Man-yi's history, meteorologically
speaking, was the evolution of its eye from a pinhole eye only 6 nm
in diameter on the 4th to a huge 65-nm diameter eye on the 7th. An
eyewall replacement cycle seems to have been ongoing during part of
this period. The JTWC warning issued at 05/0600 UTC noted that an
apparent eyewall replacement cycle was beginning with visible imagery
depicting a developing convective ring 33 nm in diameter. Six hours
later the eyewall had collapsed in the eastern quadrant. The 1800
UTC warning noted that a TRMM pass at 1315 UTC had depicted a nearly
concentric rainband outside a large eye feature. The diameter of the
eye had grown to 45 nm at 06/0600 UTC and to 65 nm at 0000 UTC on the
7th. According to Mark Lander, once a tropical cyclone reaches this
"annular" stage, the large eye condition tends to be stable. Also,
Mark noted that this particular type of tropical cyclone evolution is
fairly common in the region of the Ryukyu Islands--many typhoons with
very large eyes have crossed Okinawa. Typhoon Man-yi was located not
all that far from the primary "truck-tire" region.
D. Comparisons Between JTWC and Other Centers
---------------------------------------------
Center position coordinates were in excellent agreement between the
various warning agencies throughout the life of Man-yi. As usual, the
intensity estimates between JTWC and JMA agreed fairly well during the
earlier stages of the cyclone and during the weakening phase. JMA's
peak 10-min mean sustained wind estimate was 80 kts from 04/1200 UTC
through 06/0000 UTC, whereas, as noted above, JTWC's peak 1-min avg
MSW estimate was 115 kts. JMA's reported intensities also do not show
the double peak as indicated by JTWC: JMA's intensity estimates
remained at 75 kts during the storm's second intensification phase
reported by JTWC. NMCC's peak 10-min mean MSW was 100 kts from
04/1200 through 05/1200 UTC. This agrees very closely with JTWC's
peak 1-min avg MSW of 115 kts; however, neither do NMCC's intensities
reflect the second peak, remaining at 80 kts through this period.
E. Damage and Casualties
------------------------
Typhoon Man-yi passed through the northernmost Marianas Islands on
3 and 4 August during the time at which it was becoming a rather
intense typhoon; however, I have received no reports of any damage or
casualties that might have resulted. If any become available later,
they will be reported in a future summary.
Tropical Storm Usagi (TC-13W / TS 0110)
8 - 11 August
----------------------------------------
Usagi: contributed by Japan, is the Japanese word for rabbit
A. Origins
----------
A STWO issued by JTWC at 0600 UTC on 8 August mentioned that an area
of convection had developed and persisted in the South China Sea just
west of Luzon. Animated visible imagery depicted organized convection
associated with a possible LLCC in a region of weak to moderate
vertical shear. At 1800 UTC the disturbance was located approximately
330 nm south of Hong Kong with animated enhanced infrared imagery
showing new deep convection developing west of the LLCC. JTWC upgraded
the development potential to fair at this time.
The first warning on TD-13W was issued at 09/0000 UTC with the
center located about 300 nm south of Hong Kong. The MSW was estimated
at 25 kts and the depression was moving west at 12 kts. (NOTE: The
JMV file, a sort of working Best Track, indicates that JTWC retro-
actively considers the system to have become a depression at 0600 UTC
on 8 August about 400 nm south-southeast of Hong Kong.) The second
warning (at 09/0600 UTC) noted that the center of TD-13W was fully-
exposed about 30 nm east of the deep convection. Six hours later the
center was still exposed but a weak banding feature was attempting to
wrap into the vortex from the southwest. Upper-level easterlies of 30
to 40 kts over the region were continuing to hamper further development
of the depression.
Organization had improved slightly by 1800 UTC and JTWC increased
the MSW to 30 kts. A SSM/I pass at 09/2240 UTC depicted a partially-
exposed center with deep convection still sheared to the west; CI
estimates had risen to 30 and 35 kts around this time. By 0600 UTC
on the 10th animated visible imagery indicated that the LLCC was
situated beneath the extreme northern edge of the deep convection.
JTWC relocated the center to a position about 70 nm west of the
previous warning position, just off the Vietnamese coast south-
southwest of Hainan Dao. CI estimates were 35 kts and JTWC, NMCC
and JMA all upgraded the system to a tropical storm with JMA assigning
the name Usagi. Six hours later HKO had also upgraded Usagi to a
40-kt tropical storm.
B. Track and Intensity History
------------------------------
Usagi's career as a tropical storm was quite short-lived, however.
The storm reached its peak intensity of 40 kts (per JTWC) at 1200 UTC
on the 10th when it was located about 80 nm east of the Vietnamese
coast and moving westward at 11 kts. Enhanced infrared imagery showed
a primary banding feature wrapping in toward the center from the south-
west. By 1800 UTC the center had moved inland about 155 nm south of
Hanoi and was weakening, so JTWC issued their final warning with Usagi
continuing to move farther inland at 20 kts. Tropical Storm Usagi
tracked westward throughout its life along a monsoon trough south of a
weakening low- to mid-level ridge. There were some synoptic reports
received of winds to 35 kts as the weak tropical storm made landfall.
C. Comparisons Between JTWC and Other Centers
---------------------------------------------
Center position coordinates were in good agreement between the
several warning centers throughout the life of Usagi despite the fact
that the system remained weak. JMA's maximum 10-min avg MSW was
35 kts, which represents excellent agreement with JTWC's peak 1-min avg
MSW of 40 kts. HKO and NMCC, however, reported a slightly stronger
system with peak 10-min mean winds of 40 and 45 kts, respectively.
D. Damage and Casualties
------------------------
I have been unable to locate any reports of damage or casualties
resulting from the landfall of Tropical Storm Usagi in Vietnam. There
was flooding reported in that country during the month of August, but
I have found no press reports which link the flooding with Usagi.
Typhoon Pabuk (TC-14W / TY 0111)
14 - 24 August
---------------------------------
Pabuk: contributed by Laos, is the name of a large freshwater fish
that lives in the Mekong River
A. Origins
----------
JTWC issued a special STWO at 2100 UTC on 13 August for an area of
convection about 130 nm north-northwest of Saipan which had developed
rapidly over the previous 6-12 hours. Animated infrared satellite
imagery depicted rapidly improving organization with a convective band
developing south and east of a LLCC. Synoptic data indicated that
the LLCC was located within a broad monsoon depression with 20-kt
westerly winds south of the center and 25-30 kt winds east of the
LLCC associated with some deep convection. Water vapor imagery and
a 200-mb analysis indicated that an anticyclone was developing over
the disturbance. Since the disturbance appeared to be rapidly
developing and environmental conditions favored further strengthening,
the development potential was immediately upgraded to good and a TCFA
was issued shortly afterward.
The first warning on TD-14W was issued at 14/0000 UTC placing the
center 180 nm north of Saipan. CI estimates were 25 and 30 kts, and
animated water vapor imagery indicated good outflow, particularly on
the equatorward side. A 13/2012 UTC QuikScat pass showed a well-
defined LLCC with extensive near-gale-force gradient westerlies south
of the center. JTWC upgraded TD-14W to a tropical storm at 0600 UTC
with the center located about 210 nm north of Saipan, moving north at
6 kts. JMA and NMCC upgraded the cyclone to a tropical storm six
hours later with JMA assigning the name Pabuk.
B. Track and Intensity History
------------------------------
Initially located in a region of weak steering between mid-level
ridges to the north-northwest and east, Tropical Storm Pabuk moved
slowly northward through the northernmost Marianas as a minimal
tropical storm. At 14/1200 UTC the storm was relocated farther to
the west along the western edge of the deep convection. Animated
infrared imagery depicted deep convective bands south and east of
the LLCC while animated multi-spectral imagery indicated that a
broad circulation had not fully consolidated in the monsoon trough.
A 14/0841 UTC QuikScat pass showed a LLCC with troughing to the west
along the monsoonal axis. Water vapor imagery depicted good outflow
equatorward of the center with strong upper-level westerlies to the
north. At 15/0000 UTC the center was relocated 47 nm to the west of
the previous warning position based on the appearance of a partially-
exposed LLCC.
The cyclone turned to a west-northwesterly track on 15 August as a
ridge to the north strengthened. By 1200 UTC water vapor imagery and
a 200-mb analysis indicated good outflow with the presence of a weak
anticyclone aloft. Pabuk steadily intensified and reached typhoon
intensity (per JTWC) at 1800 UTC on the 15th when it was centered about
425 nm northwest of Saipan. (NMCC upgraded the storm to a typhoon at
0600 UTC on 16 August while JMA waited until 1800 UTC to classify Pabuk
as a typhoon.) According to JTWC Pabuk reached an initial peak
intensity of 85 kts at 17/0000 UTC when the storm was centered about
575 nm northwest of Saipan. However, the storm began to show signs
of weakening and JTWC lowered the MSW to 75 kts at 1200 UTC and to
70 kts at 1800 UTC. During this time Pabuk continued to track
slowly west-northwestward in easterly flow south of the mid-level ridge
to the north with some weak southerly flow generated by a ridge to the
east-southeast. An upper-level shortwave trough over eastern China was
forecast to move into the East China Sea and develop a weakness in the
mid-level ridge over western Japan.
By early on the 18th Pabuk was beginning to show signs of
strengthening once more. The JTWC warning at 0600 UTC noted that a
banding eye feature was visible in satellite imagery, and at 1200 UTC
animated imagery depicted a developing eyewall with deep convection
forming in all quadrants. Eyewall convection had improved by 1800 UTC
and a 75-nm irregular eye was visible. Typhoon Pabuk reached its peak
intensity of 95 kts at 0600 UTC on 19 August. Pabuk was a large storm,
sporting an eye 50 nm in diameter with gales covering an area about
500 nm across; storm-force winds extended outward about 100 nm from the
center. The 20/0000 UTC warning noted that the storm exhibited an
irregular eye 55 nm in diameter with deep convection cycling diurnally.
Animated water vapor imagery depicted excellent dual-channel outflow.
On the 19th Pabuk began moving more northwestward toward a
developing weakness in the ridge to the north, and by 1200 UTC on
20 August the storm was moving north-northeastward into a weakness
created by a mid-latitude trough over the Sea of Japan. Winds were
down to 80 kts by 1200 UTC; a SSM/I pass had revealed that most of
the deep convective bands were in the northern semicircle and that the
eyewall was eroding. Pabuk began to weaken rather rapidly as it
approached the southern coast of Japan. The center of the cyclone
just reached the coast of Japan on the southern tip of the peninsula
south of Osaka around 21/1200 UTC with peak winds estimated at 55 kts.
(JMA's 10-min avg MSW at the time was 60 kts.) The weakening storm
turned more to the northeast and later east-northeast, skimming along
the coast of southern Honshu. At 22/0600 UTC Pabuk's center passed
just south of Tokyo and by 1200 UTC was back over the Pacific east of
Honshu, moving east-northeastward at 19 kts and rapidly losing tropical
characteristics. JTWC issued their final warning at 1800 UTC with the
now-extratropical Pabuk located about 80 nm east-southeast of Misawa,
Japan, and moving north-northeastward at 24 kts. The extratropical
renmants of Pabuk continued moving northeastward and slowly weakened.
By 24/1200 UTC the former tropical cyclone was a weak LOW in the
western Bering Sea near the northeastern coast of the Kamchatka
Peninsula.
C. Meteorological Aspects
-------------------------
At 21/0000 UTC Murotomisaki reported sustained 10-min mean winds
of 60 kts with an attendant SLP of 976 mb. At the time of the
observation, Pabuk's center was about 100 nm south-southeast of the
station. Synoptic reports as the weakening cyclone approached and
moved over coastal Honshu allowed forecasters to keep a good handle on
the pressure. Synoptic reports around 21/0600 UTC indicated that the
CP was around 970 mb. This had risen to 981 by 22/0000 UTC and to
988 mb at 1200 UTC after Pabuk had exited Japan and was back over
Pacific waters.
Per JTWC's warnings, Pabuk was at its peak intensity of 95 kts from
19/0600 through 20/0600 UTC. The minimum CP estimated by JMA was
955 mb at 17/0600 UTC, but then remained at 960 mb through 1200 UTC
on the 20th.
NOTE: After I had this report on Pabuk essentially written, I
discovered in my files an e-mail from Julian Heming to Pete Donaldson
which raises some questions about the intensity of the cyclone early
in its life. JTWC initiated warnings on TD-14W at 14/0000 UTC and
upgraded the depression to a tropical storm on the second warning at
0600 UTC. However, according to Julian's e-mail, ship WFLG reported
winds of 40 kts at 13/1800 UTC, 39 kts at 13/2100 UTC, and a south
wind of 46 kts at 14/0000 UTC. The ship's position was well south
and east of JTWC's estimated center location, and it is possible that
since Pabuk was developing as (or in) a large monsoon depression, JTWC
did not consider the gale-force winds to be representative of the
developing tropical cyclone's intensity.
D. Comparisons Between JTWC and Other Centers
---------------------------------------------
Center position coordinates were in fairly good agreement between
JTWC, NMCC and JMA during the life of Typhoon Pabuk. As noted above,
JMA did not upgrade Pabuk to a typhoon until 24 hours after JTWC had
done so; otherwise, intensity estimates were in fairly good agreement
between the two warning centers. During Pabuk's initial peak of
85 kts, JMA's reported 10-min avg winds were around 70-75 kts, which
represents very good agreement. However, JMA's intensity remained at
70 kts during the time Pabuk reached its peak JTWC intensity of 95 kts.
The peak MSW (10-min avg) reported by NMCC was 80 kts for a full 3-1/2
day period, extending from 17/0000 through 20/1200 UTC.
E. Damage and Casualties
------------------------
Pabuk moved through the Northern Marianas as a minimal tropical
storm early in its career, but I have received no reports of damage
of casualties from the islands as a result of the storm. Pabuk was
responsible for seven deaths in Japan as it swept the southern coast
of Honshu. Hundreds of homes were flooded and rail, sea, and air
traffic were hampered.
Super Typhoon Wutip (TC-16W / TY 0112)
26 August - 4 September
---------------------------------------
Wutip: contributed by Macau, is the Macanese word for butterfly
A. Origins
----------
An area of convection developed over the Philippine Sea west of Guam
on 25 August; a STWO issued by JTWC at 0600 UTC noted that a weak LLCC
with associated scattered deep convection lay within a broad monsoon
circulation. A 200-mb analysis indicated weak to moderate vertical
shear over the region. The system began to develop fairly quickly;
the development potential was upgraded to fair at 26/0100 UTC, and a
TCFA was issued at 0400 UTC, upgrading the potential for development to
good. The disturbance was centered approximately 340 nm north-
northwest of Guam at the time. Another 200-mb analysis indicated good
diffluence aloft with a possible anticyclone forming over the area.
Deep convection was scattered but improving in organization; moderate
vertical shear was still inhibiting development somewhat.
JTWC issued the first warning on TD-16W at 0000 UTC on the 27th,
locating the center about 330 nm northwest of Guam. The initial MSW
of 30 kts was based on CI estimates of 25, 30 and 35 kts. Organization
had improved markedly over the past six hours with an increase in deep
convection noted. (NOTE: The JMV file from JTWC classifies the system
as a 25-kt tropical depression at 26/1800 UTC--six hours prior to the
issuance of the first warning.)
JTWC upgraded the depression to a tropical storm at 27/0600 UTC with
the center located approximately 325 nm northwest of Saipan. The MSW
was estimated at 35 kts--this was upped to 45 kts six hours later.
Also at 1200 UTC, JMA upgraded the system to Tropical Storm Wutip with
40-kt winds (10-min avg), and NMCC also classified Wutip as a tropical
storm at this time.
B. Track and Intensity History
------------------------------
Throughout its life Wutip tracked generally northeastward along a
reverse-oriented monsoon trough under the influence of a mid-level
ridge to its southeast. Tropical Storm Wutip's intensification
proceeded at a rapid pace. An eye feature was seen developing at
28/0000 UTC so JTWC upgraded Wutip to a typhoon only 18 hours after
it had been declared a tropical storm. The fledgling typhoon was
located slightly more than 100 nm west of the northernmost Marianas
Islands at the time. By 0600 UTC a 12-nm irregular cloud-filled eye
had become visible, and a 28/1055 UTC SSM/I pass depicted a primary
banding feature wrapping in toward the vortex center from the north-
west. The MSW was upped to 90 kts at 1200 UTC and to 115 kts at
1800 UTC when Wutip was centered about 250 nm southeast of the island
of Iwo Jima.
Continuing to the northeast, Wutip had reached a point about 250 nm
east-southeast of Iwo Jima by 29/0600 UTC. Based on CI estimates of
127 and 140 kts, JTWC increased the MSW to 130 kts, making Wutip the
first super typhoon of the year. The warning noted that interaction
with an upper-level trough to the northwest had resulted in rapid
intensification of the system. Gales covered an area 180 nm in
diameter around a well-defined 10-nm round eye. The diameter of the
area of 50-kt winds was 100 nm while the maximum radius of 100-kt
winds was estimated at 25 nm. Wutip was maintained as a super typhoon
for only six hours; at 1200 UTC all the CI numbers were 6.5 so the
MSW was reduced to 125 kts. Typhoon Wutip's center passed about
300 nm due east of Iwo Jima at 29/1800 UTC.
By 30/0000 UTC the storm displayed a 20-nm eye with warming cloud
tops; however, one CI estimate of 140 kts was received so the MSW
remained at 125 kts, but was lowered slightly to 120 kts six hours
later. As Typhoon Wutip continued to move northeastward away from the
tropics and into the subtropical zone, it began to weaken. At 1800
UTC on 31 August animated infrared imagery depicted a reduction in the
coverage of deep convection; the intensity had been reduced to 75 kts
by that time. The JTWC warning at 0000 UTC on 1 September noted that
Wutip was beginning to enter the early stages of extratropical
transition, although at 0600 UTC the storm still had a fairly well-
defined banding eye feature with the MSW estimated to be 70 kts at
the time.
A SSM/I pass at 01/1004 UTC revealed that deep convection was
confined to the eastern semicircle, and by 1800 UTC dry air entrainment
into the western semicircle had led to further weakening. JTWC down-
graded Wutip to a 60-kt tropical storm at this time with further
weakening forecast. The center had become partially-exposed by
02/0000 UTC, and Wutip had become more-or-less completely extratropical
by 1800 UTC. JTWC issued the final warning on the cyclone at 1800
UTC, placing the center almost 900 nm east of Tokyo. The remnants
of Wutip continued moving northeastward as a slowly weakening extra-
tropical gale. By 0600 UTC on 4 September the system, still producing
winds to 35 kts, had crossed the Dateline well to the south of the
westernmost Aleutian Islands.
To summarize, Super Typhoon Wutip's peak intensity of 130 kts (per
JTWC's warnings) was reached on 29 August at 0600 UTC. The MSW was
estimated at 115 kts or greater from 28/1800 UTC through 30/1800 UTC.
The minimum CP assigned by JMA was 930 mb from 29/1200 UTC through
30/0600 UTC.
C. Comparisons Between JTWC and Other Centers
---------------------------------------------
Center position coordinates were in very good agreement between the
various warning centers throughout the life of Wutip. Intensity
estimates between JTWC and JMA agreed well during the earlier and
latter stages of the storm's history. JMA's peak estimated 10-min avg
wind was 90 kts from 29/1200 through 30/0600 UTC. This was slightly
after the time of JTWC's peak of 130 kts (29/0600 UTC). A little
surprisingly, NMCC's maximum 10-min avg MSW estimate was also only
90 kts--from 29/0600 through 30/1200 UTC.
D. Damage and Casualties
------------------------
Around the time that Wutip was reaching typhoon intensity, it passed
close enough to the Northern Marianas such that the outer fringes of
the storm would have affected the islands. However, I have not
received any reports of damage or casualties resulting from Wutip. If
any become available later they will be reported in a future summary.
Tropical Storm Sepat (TC-17W / TS 0113)
27 August - 1 September
----------------------------------------
Sepat: contributed by Malaysia, is the name of a freshwater fish
often found in rivers and swampy areas with lots of weeds,
and also in paddy fields
A. Origins
----------
A very active and extensive monsoon trough covered most of the
Western North Pacific in late August. Tropical Depression 15W as
well as named storms Wutip, Sepat, and Fitow all had their origins as
circulations in the trough. There were numerous circulations, ranging
from small eddys with only one or two thunderstorms to the intense
Super Typhoon Wutip. Tracing the origin of Tropical Storm Sepat using
the daily STWOs issued by JTWC led to a long journey around the NWP
basin. The discussion below is based on what I gleaned from the STWOs,
using the "previously located near" coordinates to piece together the
continuity from day to day. However, it seems fantastic that one
single, weak LLCC could make such a tour of the Western Pacific for
over a week, at times making a quantum leap of several hundred miles
from one day to the next. Given the numerous circulations crawling
around in the huge monsoon trough, which some meteorologists dubbed
"a marvel of nature", it seems likely that there were flare-ups of
convection here and there which may or may not always have been
directly traceable to a flare-up seen the previous day.
The STWO issued by JTWC at 0600 UTC on 19 August mentioned that an
area of convection was developing very deep in the tropics roughly
100 nm south of Pohnpei. Bands of deep convection were forming south
of a broad LLCC. A 200-mb analysis indicated 20 kts of easterly shear
over the area. The STWO for 20/0600 UTC indicated that the area of
convection was southwest of Chuuk--over 500 nm west of the previous
day's position. The existence of a broad LLCC was supported by
animated visible imagery and synoptic reports. At 0600 UTC on the
21st the area of convection was relocated about 350 nm to the west-
northwest to a position south-southwest of Guam. Moderate to strong
vertical shear overlay the disturbance.
By 22/0600 UTC the disturbance had migrated east-northeastward to a
point south-southeast of Guam. A 22/0000 UTC surface analysis had
indicated a broad LLCC; however, a QuikScat pass had been unable to
resolve a single circulation but rather had revealed multiple areas
of turning within the monsoon trough. An interim STWO issued at
2000 UTC relocated the disturbance to a position farther north over
the Northern Marianas. Synoptic data indicated that a weak LLCC had
formed in the monsoon trough and appeared to be merging with a shear
line extending northeastward from the islands. Several bursts of
convection had been noted along the trough.
At 0600 UTC on the 23rd the area of convection was relocated to a
point a couple hundred miles east of the Marianas. The majority of
the deep convection remained south of the LLCC in low-level convergent
flow. The system remained quasi-stationary on the 24th, but by 0600
UTC on 25 August had again been repositioned a couple hundred miles
to the east with little change in structure. At 0600 UTC on the 26th
the disturbance was relocated about 400 nm to the east of the previous
day's position. The LLCC was by then located about 1000 nm east of
the Marianas and had moved into a region of favorable vertical shear.
JTWC upgraded the development potential to fair. A TCFA was issued
at 26/1700 UTC with the LLCC estimated to be about 225 nm west of
Wake Island. Animated satellite imagery indicated a convective band
forming southwest of the LLCC with improving overall organization
noted. Vertical shear was weak and the system had good outflow aloft.
JTWC issued the first warning on TD-17W at 27/0000 UTC with the
center located about 250 nm northwest of Wake Island and moving north-
northwestward at 14 kts. The initial MSW of 30 kts was based on CI
estimates of 25 and 30 kts. JTWC upgraded the depression to a
tropical storm at 1800 UTC when it was centered approximately 400 nm
northwest of Wake Island and moving northward at 8 kts. Six hours
later JMA upgraded the cyclone to Tropical Storm Sepat. JTWC upped
the MSW to 45 kts (which turned out to be the peak intensity) at the
same time based on CI estimates of 45 and 55 kts. Also, a recent
QuikScat pass had shown uncontaminated winds of 40 kts. A 200-mb
analysis indicated that Sepat was experiencing enhanced outflow due
to a TUTT lying to the northwest. NMCC was the last warning agency
to upgrade Sepat to tropical storm status--they did so at 0600 UTC
on 28 August.
B. Track and Intensity History
------------------------------
Tropical Storm Sepat tracked on a course just west of due north for
its entire life span as a tropical cyclone. The storm was steered on
its poleward course by a strong mid-level HIGH centered generally east-
northeast of the cyclone. As noted above the maximum MSW assigned by
JTWC was 45 kts, and the peak 10-min avg MSW estimated by JMA was
40 kts. At 28/0600 UTC satellite imagery revealed new deep convection
building over the vortex center, but a 28/0915 UTC SSM/I pass depicted
a significant decrease in overall coverage of convection, although low-
level cloud lines were still well-defined. By 29/0000 UTC Sepat had
moved to a position about 1000 nm west of Midway Island. A SSM/I pass
at 28/2009 UTC revealed only scattered deep convection associated with
the circulation. JTWC decreased the intensity to 35 kts at this time.
By 1800 UTC Sepat was located approximately 1250 nm west-northwest
of Midway and moving north-northwestward at 29 kts. The concurrent
JTWC warning indicated that the storm was becoming extratropical.
JTWC issued their final warning at 0000 UTC on the 30th with Sepat
located about 870 nm east-southeast of Misawa, Japan. The initial
warning estimated the MSW at 25 kts, but later receipt of QuikScat
data indicating winds to 30 kts, and a ship report of 30 kts, led to
the issuance of an amended warning raising the winds to 30 kts.
However, Sepat was forecast to be completely extratropical in 12 hours,
so JTWC did not issue any further warnings. JMA, however, maintained
Sepat as a 40-kt tropical storm for another 30 hours as the system
turned to the east-northeast and accelerated. JMA deemed Sepat to be
extratropical at 31/1200 UTC, and the final reference to this system
in JMA's High Seas Bulletins placed it near the Dateline south of the
Aleutians at 0000 UTC on 1 September as a weakening gale.
C. Comparisons Between JTWC and Other Centers
---------------------------------------------
Center position coordinates were in good agreement between JTWC,
JMA and NMCC for Tropical Storm Sepat. And, as noted above, intensity
estimates between JTWC and JMA were also in excellent agreement,
although JMA carried the storm as a tropical entity for over a day
longer than JTWC. NMCC's intensity estimates were the lower of the
three TCWCs--Sepat was maintained as a minimal 35-kt tropical storm
for the entire period in which NMCC issued warnings.
D. Damage and Casualties
------------------------
Tropical Storm Sepat did not affect any populated areas, and no
damage or casualties are known to have resulted from this tropical
cyclone.
Tropical Storm Fitow (TC-18W / TS 0114)
28 - 31 August
----------------------------------------
Fitow: contributed by the Federated States of Micronesia, is the
Yapese name for a beautiful fragrant flower
A. Origins
----------
The STWO issued by JTWC at 0600 UTC on 26 August noted that an area
of convection had developed west of Luzon in the South China Sea.
Synoptic data and satellite imagery indicated a broad LLCC within the
monsoon trough. CIMSS shear products indicated moderate vertical
shear over the region. Disturbed weather had persisted in the northern
South China Sea for a good portion of the month of August. As noted
in the introductory section on NWP activity for August, there was
possibly a connection between the circulation(s) classified by PAGASA
as Tropical Depression Jolina and the later Tropical Storm Fitow.
By 0600 UTC on the 27th the system had drifted slightly to the west
of the previous day's position. JTWC upgraded the development
potential to fair since convection was increasing in organization near
the LLCC. By 28/0600 UTC the LLCC was again farther to the west at
a position about 300 nm south-southwest of Hong Kong. Animated visible
imagery depicted a broad LLCC with associated cloudiness along the
periphery of the system. Synoptic data also indicated monsoon
depression characteristics. A 200-mb analysis revealed improving
environmental conditions conducive to development. HKO was the first
warning agency to issue warnings--at 28/1200 UTC they issued the first
warning on a 25-kt depression located about 285 nm south-southwest of
Hong Kong. JTWC issued a TCFA for the system at 0900 UTC on the
28th.
JTWC issued the first warning on TD-18W at 29/0000 UTC, locating the
center approximately 210 nm southwest of Hong Kong, moving west-
northwestward at 7 kts. JMA and NMCC also classified the system as a
tropical depression at 0000 UTC. By 1200 UTC the center of TD-18W was
located over the northeastern coast of Hainan Dao. JTWC assessed the
MSW to be 25 kts based on satellite intensity estimates and synoptic
ship reports of 25 kts. The depression subsequently moved slowly
westward across the northern portion of the island.
By 0600 UTC on 30 August the depression's center was near the north-
west coast of Hainan Dao, moving out into the Gulf of Tonkin. NMCC
upgraded the system to a 35-kt tropical storm at this time with JTWC
and HKO both upgrading the depression to a tropical storm at 1200 UTC.
The center was by this time over the Gulf of Tonkin moving slowly
northwestward. Convection associated with the LLCC had increased and
there was good outflow to the south. Also, SSM/I and TRMM imagery
revealed a more organized LLCC embedded in the convection.
B. Track and Intensity History
------------------------------
By 1800 UTC Tropical Storm 18W had turned to a slow northward track
toward the coast of China. JTWC estimated the MSW at 35 kts based on
CI estimates of 35 and 45 kts. At 31/0000 UTC both JTWC and NMCC
increased the intensity to 40 kts; also at 0000 UTC, JMA upgraded the
system to a tropical storm, naming it Fitow. By 0600 UTC on the 31st,
Tropical Storm Fitow's center was on the coast of China near Dongxing,
moving north-northwestward at 6 kts. JTWC maintained 40 kts as the
MSW based on satellite intensity estimates of 35 and 45 kts and a
synoptic report of 40 kts from near the center. JMA, however, down-
graded Fitow to a 30-kt depression at 0600 UTC. By 1200 UTC Fitow was
inland and dissipating over southwestern China and all the other TCWCs
downgraded the system to depression status. This was JTWC's final
warning, but NMCC and HKO each issued one more bulletin on Fitow at
1800 UTC.
C. Meteorological Aspects
-------------------------
Huang Chunliang has sent me several meteorological observations
from southern China. The depression's center first made landfall
near Wenchang City in Hainan Province around 1130 UTC on 29 August.
According to some information Chunliang received from NMCC, Fitow
dropped in excess of 700 mm of rain at some location (site unknown)
on the island of Hainan--a very rare occurrence.
The storm's final landfall occurred just southwest of Beihai City
(21.5N, 109.1E) around 31/0300 UTC. At 31/0000 UTC Beihai recorded
a SLP of 988 mb with sustained winds (presumably a 10-min avg) of
23 kts, gusting to 37 kts. At 0600 UTC the station reported a SLP
of 996 mb with mean winds of 17 kts, gusting to 47 kts.
Dongfang City recorded 815.3 mm of rainfall during the 8-day
period from 27/1700 UTC through 2000 UTC on 4 September. A location
within Changjiang County recorded 831.1 mm during the 72-hour period
ending at 0800 UTC on 31 August with 404 mm falling during a 12-hour
period on the 30th. Several locations recorded rainfall amounts in
excess of 400 mm in the 72 hours ending at 31/0800 UTC. Wenchang
City on Hainan Dao recorded 245 mm in the 30 hours ending at 1400
UTC on 29 August.
Several stations in the Hong Kong area reported winds gusting in
excess of gale force on 28 and 29 August when the depression was
nearest to Hong Kong. Some of these observations were: 44 kts at
Cheung Chau, 41 kts at North Point, 52 kts at Tai Mo Shun, and 54 kts
at Waglan Island. Sustained winds in general were well below gale
force except at Tai Mo Shun where mean winds reached 34 kts. Several
stations in the Hong Kong area neared or exceeded 200 mm of rainfall
for storm totals with the highest being 255 mm at Sha Tin and 227 mm
at Jordan Valley. More detailed information can be found in a storm
report on Fitow located on HKO's website (see Section E below for
the URL).
D. Comparisons Between JTWC and Other Centers
---------------------------------------------
Center position coordinates were in fairly good agreement between
the several warning centers for Fitow, especially considering that it
was a weak, disorganized system. Although JMA classified the cyclone
as a tropical storm for only one warning cycle, the difference between
it and the other TCWCs was only a matter of 5 kts--it just happened to
involve that very arbitrary but very important threshold of 34 kts.
NMCC was the first agency to upgrade the system to tropical storm
status (at 30/0600 UTC), and JTWC and HKO did so six hours later.
Twelve hours elapsed before JMA issued their only tropical storm
warning on the system, officially naming it Fitow. The maximum
intensity estimated for Fitow was 40 kts, from both JTWC (1-min avg)
and NMCC (10-min avg); the peak 10-min mean winds reported by JMA and
HKO remained at 35 kts.
E. Damage and Casualties
------------------------
As of 31 August, total economic losses in Hainan were estimated at
1.367 billian yuan. Over two million residents of the province were
seriously affected by the storm, 1300 houses were destroyed, 106.5
thousand hectares of farmland were badly stricken, and 26,700 head of
livestock were reported dead. In Guangdong Province almost a million
and a half residents were seriously affected with 2380 houses toppled.
There were also four deaths reported in the province. In the Hong
Kong area two persons drowned when they were swept away by waves.
The Hong Kong Observatory has prepared a report on Tropical Storm
Fitow which can be found at the following website:
http://www.weather.gov.hk/informtc/fitow/fitow.htm>
(A special thanks to Chunliang for sending me all the information
on the effects of this tropical storm.)
***********************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for August: No tropical cyclones
***********************************************************************
SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E
Activity for August: No tropical cyclones
***********************************************************************
NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E
Activity for August: No tropical cyclones
***********************************************************************
NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E
Activity for August: No tropical cyclones
***********************************************************************
SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E
Activity for August: No tropical cyclones
***********************************************************************
EXTRA FEATURE
In order to shorten the amount of typing in preparing the narrative
material, I have been in the habit of freely using abbreviations and
acronyms. I have tried to define most of these with the first usage
in a given summary, but I may have missed one now and then. Most of
these are probably understood by a majority of readers but perhaps a
few aren't clear to some. To remedy this I developed a Glossary of
Abbreviations and Acronyms which I first included in the July, 1998
summary. I don't normally include the Glossary in most months in
order to help keep them from being too long. If anyone would like to
receive a copy of the Glossary, please e-mail me and I'll be happy
to send them a copy.
***********************************************************************
AUTHOR'S NOTE: This summary should be considered a very preliminary
overview of the tropical cyclones that occur in each month. The cyclone
tracks (provided separately) will generally be based upon operational
warnings issued by the various tropical cyclone warning centers. The
information contained therein may differ somewhat from the tracking and
intensity information obtained from a "best-track" file which is based
on a detailed post-seasonal analysis of all available data. Information
on where to find official "best-track" files from the various warning
centers will be passed along from time to time.
The track files are not being sent via e-mail. They can be retrieved
in the following manner:
(a) FTP to: hrd-type42.nhc.noaa.gov [140.90.176.206]
(b) Login as: anonymous
(c) For a password use your e-mail address
(d) Go to "data" subdirectory (Type: cd data)
(e) Set file type to ASCII (Type: ascii)
(f) Transfer file (Type: get remote_file_name local_file_name )
(The files will be named with an obvious nomenclature--using
August as an example: aug01.tracks)
(g) To exit FTP, type: quit
Both the summaries and the track files are standard text files
created in DOS editor. Download to disk and use a viewer such as
Notepad or DOS editor to view the files.
The first summary in this series covered the month of October,
1997. If anyone wishes to retrieve any of the previous summaries,
they may be downloaded from the aforementioned FTP site at HRD. The
summary files are catalogued with the nomenclature: aug01.sum, for
example.
Back issues can also be obtained from the following websites
(courtesy of Michael Bath, Michael V. Padua, Tom Berg, Michael
Pitt, and Rich Henning):
http://australiasevereweather.com/cyclones/>
http://www.typhoon2000.ph> OR http://66.40.4.61>
http://www.hurricanealley.net/>
http://www.qisfl.net/home/hurricanemike>
http://www.met.fsu.edu/gsc/Docs/Grads/henning/cyclones/>
NOTE: The URL for Michael V. Padua's Typhoon 2000 website has
changed slightly once more.
Another website where much information about tropical cyclones may
be found is the website for the UK Meteorological Office. Their site
contains a lot of statistical information about tropical cyclones
globally on a monthly basis. The URL is:
http://www.met-office.gov.uk/sec2/sec2cyclone/sec2cyclone.html>
TROPICAL CYCLONE REPORTS AVAILABLE
JTWC now has available on its website the complete Annual Tropical
Cyclone Report (ATCR) for 2000 and a report on the 2000-2001 season in
the Southern Hemisphere. ATCRs for earlier years are available also.
The URL is: http://199.10.200.33/jtwc.html>
Also, TPC/NHC has available on its webpage nice "technicolor"
tracking charts for the 2000 Atlantic and Eastern North Pacific
tropical cyclones; also, preliminary storm reports for all the 2000
Atlantic and Eastern North Pacific cyclones are now available, as
well as track charts and reports on storms from earlier years.
The URL is: http://www.nhc.noaa.gov>
Prepared by: Gary Padgett
E-mail: [email protected]
Phone: 334-222-5327 (nights & weekends) / 850-882-2594 (weekdays)
***********************************************************************
***********************************************************************
|
Document: summ0108.htm
Updated: 27th December 2006 |
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