[Index]
Monthly Global Tropical Cyclone Summary May 2001
[Summaries and Track Data] [Prepared by Gary Padgett]
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Cyclones
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Monthly Global Tropical Cyclone Summary May 2001 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
MAY, 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: I have included the Glossary of Abbreviations and
Acronyms at the end of this summary. New acronym
added: TCFA - Tropical Cyclone Formation Alert
***********************************************************************
MAY HIGHLIGHTS
--> Intense Arabian Sea cyclone threatens west coast of India
--> Most intense May Eastern Pacific hurricane on record forms
***********************************************************************
***** Feature of the Month for May *****
RESULTS OF TROPICAL CYCLONE SURVEY - PART 1
SIZE AS A POSSIBLE CLASSIFICATION CRITERION
A few months ago I sent a little survey to several persons whom
I either knew personally or else had corresponded much with over the
past three years that I've been writing the global tropical cyclone
summaries. The following were the ones who responded, and to them
I would like to extend a special thanks for taking the time to reply:
Jeff Callaghan, Steve Ready, Matthew Saxby, Philippe Caroff, James
Franklin, David Roth, Jack Beven, Chris Landsea, Julian Heming, and
Rich Henning.
The survey was a solicitation of opinions regarding certain issues
relevant to the classification of tropical cyclones, especially
focusing on borderline type systems which in some basins may be
readily treated as tropical cyclones and not in others. The questions
that I asked in the survey were as follows (slightly reworded):
(1) Regarding subtropical cyclones or otherwise hybrid systems: How
"tropical" should one be before being classified as a tropical
cyclone?
(2) Regarding spatial distribution of gales: In how many quadrants
and how close in to the center should gales be occurring before
a system is named as a tropical storm (or cyclone)?
(3) Should monsoon depressions with gale-force winds be considered
tropical storms (or cyclones)?
(4) Should the (usually) small TUTT-generated systems of higher
latitudes be considered tropical cyclones?
(5) Regarding extremely small midget systems: Should there be a
size criterion for classification as a tropical cyclone?
All the tropical cyclone warning agencies have official terminology
and operational procedures which work well in their respective areas
of responsibility, and issuing timely and accurate warnings in real
time is certainly the primary goal of all warning centers. But the
study of tropical cyclones from a climatological and statistical
perspective and with a global scope is also very important, even if
secondary to the operational warning side of things. And such study
is quite often hampered because of inconsistencies in the manner in
which the above types of systems are treated between the various
warning centers (or sometimes even by a given center).
My purpose was to try to get a little dialogue going regarding some
of those issues which I have come to perceive as "sticking points" that
need some sort of consensus if the goal of a reasonably consistent
global definition of a tropical cyclone is ever to be attained. I am
concerned here with systems whose winds have reached gale intensity
(34 kts or higher) and normally would be assigned names as tropical
storms (tropical cyclones in WMO Region 5) by the responsible warning
center (except of course in the North Indian Ocean). These are the
systems which are normally archived in databases by the various
meteorological agencies and are, in a sense, the ones "remembered" by
posterity.
My plan is to utilize the responses I have received as material for
my Feature of the Month articles for about three months. However,
if anyone else has an opinion they'd like to share on any of the
above questions, I'd be happy to hear from them and will include their
responses in with the others. For this month I am limiting the
discussion to the last question: Should there be an arbitrary size
criterion for classification as a tropical cyclone?
Several of the respondents wondered why I'd even asked that
question. Admittedly, the size of a system is for the most part a
non-issue. But that question was raised many years ago in the
excellent annual summary article for the Eastern Pacific hurricane
season of 1971 written by William J. Denney, then of the NWS Forecast
Office in San Francisco. (The article was published in Monthly Weather
Review, Volume 100, Number 4, April, 1972.) In his discussion of
Tropical Storm Katrina, which was a very small, tightly-wound tropical
storm that in its early stages apparently had the magnitude of a meso-
cyclone, Mr. Denney pointed out that some storms seen in the Eastern
Pacific during the previous years since the advent of satellites had
gale-wind areas as small as 15 nm in diameter. He briefly discussed
the issue of whether there should be an arbitrary size definition to
distinguish the "ministorm" from the normal-sized tropical cyclone,
mainly because of the difficulty of following such small storms as
Katrina. However, his conclusion was that, instead of instituting a
size criterion for tropical cyclones, the problem might better be
considered a challenge to the improving skill and technology of applied
meteorology.
Australia has an outstanding example of what a midget tropical
cyclone can do: Cyclone Tracy, which practically obliterated the city
of Darwin in December, 1974. According to information received from
Jeff Callaghan, Tracy's gale radius was only about 18 nm. Other very
small but intense tropical cyclones which have struck Australia were
Kathy (1984) with a gale radius of 35 nm, and Ada (1970) with a gale
radius of 30 nm. And as Matthew Saxby pointed out, Tropical Cyclones
Steve (2000) and Rona (1999), both of which caused significant damage,
were midgets.
The most intense hurricane known to strike the United States during
the past century-and-a-half was also a very small tropical cyclone.
The famous Labor Day Hurricane which struck the Florida Keys in 1935
produced the lowest pressure ever recorded on land in the Western
Hemisphere: 892 mb. (The only lower measured pressure in an Atlantic
hurricane was the 888 mb reading obtained from a dropsonde in the eye
of Hurricane Gilbert in September, 1988.) The 1935 hurricane caused
incredible structural damage, especially to the trestles and bridges
of Henry Flagler's railroad to Key West. Engineers have estimated that
winds from 175 to 220 kts would have been required to have caused some
of the observed damage. According to Rich Henning, the gale radius
of that hurricane was on the order of 25-30 nm. The eye passed
through the middle Keys but neither Miami nor Key West reported gale
force winds. Over 400 persons died in the hurricane. Many were
literally sandblasted to death and found with no skin and no clothes
except for belt and shoes. (The last sentence found in Dunn & Miller's
_Atlantic Hurricanes_.)
None of the responses I received were in favor of an arbitrary size
criterion. David Roth wrote: "Midget phases of a tropical cyclone's
life should be treated as just that--a phase they occasionally go
through." Chris Landsea and Jack Beven both suggested some criteria
that might be applied to extremely small systems. Chris suggested that
a very small system should have some persistence, lasting at least a
day or two. If the system is (as Chris put it) "a flash-in-the-pan, it
may be that it was more of a mid-tropospheric mesoscale convective
vortex and not a true tropical cyclone."
Jack was the only person who suggested any spatial dimensions that
might be considered for defining a tropical cyclone. He writes: "My
view is that the smallest size of a tropical cyclone would be something
somewhat larger than a mid-western supercell mesocyclone--roughly
10-20 nm or so in diameter. I think the tropical cyclone has to be
large enough that the circulation is driven by multiple convective
cells, as would be the case if an eyewall or spiral band is present."
So, in summary, it appears that there is a consensus that size
should not be a criterion in defining a tropical cyclone. For the
June Feature I'll try to tackle synopsizing the opinions I received
on the subject of subtropical/hybrid cyclones, for which there does
not exist a general consensus regarding how to classify such systems.
***********************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for May: 1 possible subtropical cyclone
Atlantic Tropical Activity for May
----------------------------------
No tropical cyclones formed in the month of May in the Atlantic
basin, which is typical. Since 1886 twelve tropical storms have been
tracked in the Atlantic basin during May, three of which reached
hurricane intensity. The last May tropical storm was Arlene in 1981,
and the last hurricane in May was Alma in 1970. Several other years
have seen tropical depressions or subtropical systems develop during
May. In May of 2001, a low-pressure area formed along an old
stationary front on the 5th in the Bahamas, roughly 200 nm north of the
extreme eastern tip of Cuba, and moved east-northeastward. By late on
the 5th convection had wrapped around the eastern and northern
quadrants of the LOW. By the morning of the 6th, the cyclone had an
occluded appearance with sporadic convection just north and well to the
east of the center due to dry air wrapping around its south side.
Later on the 6th and into the 7th, the center became devoid of
convection and the low-level swirl drifted southwestward as its
upper-level circulation warmed and weakened.
Late on the 5th and throughout the 6th, this cyclone was not
connected to any frontal cloudiness on satellite imagery. That fact,
plus the fact that convection was close to the center on the 5th and
6th, led to the conclusion that the LOW was very possible subtropical
in nature.
Temperature gradient was minimal at best around the system, though
it had a decent dewpoint contrast. Most of the high winds were north
and west of the center in the Bahamas and southwest Atlantic in a
region of good pressure gradient between the LOW and a HIGH in the
eastern U. S. A cold front dropped in from the north late on the 7th
and early on the 8th, spawning a new area of low pressure which swept
this cyclone to the east, absorbing it during the morning on the 8th.
A track for this system follows. Since this was not a tropical
cyclone, I am not going to add the track to the May tracks file and
re-distribute that, but I will include it in the cyclone tracks file
for June. All the information and the track for this system was
supplied by David Roth of the Hydrometeorological Prediction Center in
Maryland. A special thanks to David for providing the information.
***********************************************************************
Storm Name: None Cyclone Number: None Basin: ATL
(Possible subtropical storm--track supplied by David Roth.)
Date Time Lat Lon Cent MSW MSW Remarks
(GMT) Press 1-min 10-min
(mb) (kts) (kts)
-----------------------------------------------------------------------
01 MAY 05 0600 23.0 N 74.0 W 1008 20
01 MAY 05 1200 23.2 N 72.9 W 1007 25
01 MAY 05 1800 23.8 N 72.2 W 1007 30
01 MAY 06 0000 24.8 N 71.7 W 1007 30
01 MAY 06 0600 25.2 N 71.0 W 1006 30
01 MAY 06 1200 25.0 N 70.2 W 1005 30
01 MAY 06 1800 24.5 N 70.1 W 1004 35
01 MAY 07 0000 24.0 N 71.0 W 1004 40
01 MAY 07 0600 24.0 N 69.8 W 1005 45
01 MAY 07 1200 24.2 N 68.8 W 1005 45
01 MAY 07 1800 24.5 N 67.9 W 1006 45
01 MAY 08 0000 25.2 N 67.3 W 1006 45
01 MAY 08 0600 26.0 N 67.0 W 1006 40
Note: The winds and pressures used were based on ship reports and
analyses prepared by HPC and MPC. Note that the maximum sustained
winds held constant at gale force until dissipation due to the
formation of another LOW to its north. Errors on the center location
should be between 30 and 60 nautical miles.
***********************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for May: 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.
Northeast Pacific Tropical Activity for May
-------------------------------------------
Over the thirty years from 1971-2000, the first tropical storm of
the season in the Northeast Pacific basin has developed in May thirteen
times, or in 43% of all seasons. The first hurricane, however, has
formed in May on only 7 occasions, or 23% of the time. The first
intense hurricane (i.e., reaching Category 3 or higher on the Saffir/
Simpson scale) had never formed in May since the advent of satellites.
The year 2001 changed that statistic: Hurricane Adolph became the
first Category 3 Eastern Pacific hurricane on record on 28 May when
its MSW reached an estimated 105 kts--24 hours later Adolph had become
the first May Category 4 hurricane on record in the North Pacific east
of the Dateline. Very fortunately for the Mexican coastline, Adolph
remained at sea with only rainbands and heavy surf affecting the coast.
The summary on Adolph following was written by John Wallace of San
Antonio, Texas. A very special thanks to John for his assistance.
Hurricane Adolph (TC-01E)
25 May - 2 June
--------------------------
A. Origins
----------
The tropical LOW that became Adolph formed along the axis of a
tropical wave, one that lingered in the Pacific west of Central
America for several days. Indeed, the UKMET had forecast tropical
storm development there as early as the 20th, long before there was
any hint of cyclogenesis. The progenitor disturbance organized
slowly but surely, and the JTWC/NPMOC issued a TCFA for the LOW at
0200 UTC on the 25th. Visible satellite imagery, along with
scatterometer data, supported the LOW's upgrade to Tropical Depression
One-E at 2100 UTC on 25 May. At this time it was located roughly
200 nm south-southwest of Acapulco, Mexico.
Though conditions were favorable for intensification, One-E was
slow to strengthen; it did not become a tropical storm for a full day
after the first advisory was issued. The center was occasionally
difficult to pinpoint, and the depression's organization waxed and
waned. Nevertheless, One-E was upgraded to Tropical Storm Adolph at
2100 UTC on 26 May, located roughly 175 nm south-southwest of Acapulco.
It was then that Adolph's previously humble existence made a dramatic
turnaround.
B. Track and Intensity History
------------------------------
Adolph intensified swiftly after its upgrade, reaching hurricane
strength only 24 hours later, at 2100 UTC on 27 May, some 185 nm
south of Acapulco. It attained a 105-kt MSW just six hours later.
Adolph initially deepened at an impressive rate: 1.46 mb per hour,
between its upgrade and 0300 UTC on the 28th. Intensification
continued until Adolph reached its peak MSW of 125 kts at 0300 UTC
on 29 May with an estimated CP of 940 mb. At this time it was
located roughly 200 nm south-southwest of Zihuatanejo, Mexico. Adolph
had a well-defined eye, and its cold CDO began to take on a so-called
"buzzsaw" appearance characteristic of very strong hurricanes.
According to the NHC, raw Objective Dvorak Numbers were as high as
T7.0, which is equivalent to a MSW of 140 kts. An SSMI pass at
0416 UTC on the 29th clearly depicted a pair of concentric eyewalls.
Adolph maintained its peak intensity for roughly eighteen hours.
The cyclone, which had been previously meandering southeastward,
began a turn to the north, then west-northwest, beginning late on
the 27th. A mid-level ridge to its north built eastward, finally
providing a steady steering current and a moderate rate of motion.
Adolph was at first a slow-mover; at 1500 UTC on the 28th, some three
days after the first advisory, Adolph was only 51 nm from its first
warning position. That being said, the change in its track warranted
the issuance of watches and warnings for the Mexican coast. A tropical
storm warning and a hurricane watch were issued for the coast at
0300 UTC on the 28th, extending from Acapulco westward to Lazaro
Cardenas. The hurricane watch was dropped at 2100 UTC on the 28th,
though Adolph continued to roughly parallel the coast. The tropical
storm warning was dropped on the next advisory, at 0300 UTC on the
29th, as Adolph reached peak intensity.
A slow weakening trend began at 2100 UTC on the 29th, though outflow
remained good. At first, the weakening was due to an eyewall
replacement cycle; soon after that, though, cooler SSTs along the
storm's track began to take their toll. Adolph's cloud tops warmed,
and convection decreased in areal extent; by 1500 UTC on the 30th the
MSW had dropped below 100 kts. Stable air-entrainment exacerbated the
process.
The cyclone assumed a more westward track on the 31st, and its
deterioration accelerated. The slight track change was no doubt due
to the increasing influence of low-level winds from a ridge to its
north. The cyclone passed about 125 nm south of Socorro Island around
1500 UTC on 31 May at minimal hurricane intensity, then, by 2100 UTC,
Adolph had weakened to tropical storm strength and its forward motion
had decreased. Ship reports suggested that the storm's circulation was
becoming distorted. At 2100 UTC on 1 June the convection-free vortex
was downgraded to a depression. The last advisory on Tropical
Depression Adolph was issued at 0300 UTC on 2 June when it was located
500 nm west-southwest of Manzanillo. A remnant swirl of low clouds
persisted for a few days thereafter.
C. Historical Tidbits
---------------------
Adolph was far and away the most intense May hurricane on record in
the Northeast Pacific basin. It is interesting to note that the
previous recordholder for May was also a hurricane named Adolph back
in 1983. The earlier Adolph peaked at 95 kts. And while on the
subject of hurricanes named Adolph, the previous Hurricane Adolph, in
1995, reached a peak intensity of 110 kts, but that storm occurred in
mid-June. This is also only the second time since 1971 that there
have been two consecutive Northeast Pacific seasons with May hurricanes
(2000-01, and 1983-84).
D. Damage and Casualties
------------------------
Though rainbands from Adolph occasionally impinged on the Mexican
coast--to say nothing of heavy surf--no casualties or damage are known
to the author.
***********************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for May: 1 tropical depression **
1 tropical storm
** - No warnings were issued on this system by any warning center.
The track and intensity estimates were provided by Roger Edson
of the University of Guam, formerly a forecaster with JTWC.
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.
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 May
-------------------------------------------
The first named tropical storm of 2001 in the Northwest Pacific
formed in mid-month in the South China Sea from a depression which had
earlier trekked westward across the central Philippines from the
Philippine Sea. While Cimaron was the first tropical storm to form
in the current year, it was not the first storm on the charts. Back in
early January Tropical Storm Soulik from late December, 2000, after
weakening, suddenly flared up and became a rather intense, albeit
brief, typhoon east of the Philippines. A report on Tropical Storm
Cimaron is given below; however, there were a couple of other systems
that warrant mention.
Roger Edson forwarded me a track he'd generated for a tropical
depression east of the Philippines. A very weak LOW was located far to
the south of Yap on 16 May. The system drifted generally north-
northwestward over the next couple of days, reaching a point about
100 nm north-northeast of Palau by 1200 UTC on 18 May. The STWO
issued by JTWC at 18/0600 UTC mentioned the disturbance, which,
according to Roger's track, likely had maximum winds of about 20 kts
at the time. The STWO for 19 May upgraded the development potential
to fair, and a Formation Alert was issued at 20/0100 UTC as convection
was beginning to increase near the LLCC and a 200-mb analysis indicated
diffluent flow aloft. The system by this time was moving northward
a few hundred miles east of the Philippines, passing about 350 nm east
of Catanduanes Island around 0000 UTC on the 21st, when, according to
Roger's track, the peak intensity of 30 kts was reached. A second
Formation Alert was issued by JTWC at 21/0100 UTC, but by 22/0000 UTC
the system was weakening and becoming extratropical about 500 nm east
of the northern tip of Luzon. (Roger's track for this system was
included in the cyclone tracks file for May. A special thanks to
Roger for sending me the information on this system.)
The other disturbance formed in the South China Sea off the coast of
Vietnam on 14 May. By 0600 UTC on the 15th a broad, fully-exposed LLCC
was located about 170 nm southeast of Da Nang with convection sheared
away toward the west. The system moved north-northwestward, roughly
parallelling the Vietnamese coast. JTWC issued a Formation Alert at
1130 UTC on 16 May when the center was estimated to be about 140 nm
northwest of Da Nang. Convection was increasing near the LLCC and the
LOW was located in an environment of weak vertical shear with good
outflow aloft. However, by 17/0530 UTC the system had moved onshore
just east of Nam Dinh, Vietnam, so the Formation Alert was cancelled.
The Central Weather Bureau of Taiwan did refer to this disturbance
as a tropical depression in one of their bulletins--none of the other
agencies classified it as a depression. (No track for this system was
included in the cyclone tracks file for May. Huang Chunliang of
Fuzhou, China, informed me that the Central Weather Bureau had
classified this system briefly as a depression--thanks to Chunliang
for alerting me to this fact.)
Tropical Storm Cimaron (TC-03W / STS 0101 / Crising)
7 - 21 May
-----------------------------------------------------
Cimaron: contributed by the Philippines, is the name of a Philippine
wild ox
A. Origins
----------
A STWO issued by JTWC at 1430 UTC on 4 May mentioned that a weak
LLCC had developed in the monsoon trough about 40 nm south of Koror.
A 200-mb analysis showed diffluent, moderate easterlies over the area.
By the next day the disturbance had migrated (or re-formed) farther to
the west to a position approximately 160 nm southeast of the Philippine
island of Mindanao. A SSM/I pass revealed deep convection but a broad,
weak LLCC; by 6 May the area was centered on the southern coast of
Mindanao. JTWC issued a Formation Alert at 1200 UTC, relocating the
center farther northward along the east coast of Mindanao. The LLCC
was accompanied by persistent convection which was displaced to the
north, and the system lay under weak to moderate upper-level easterlies
on the equatorward side of a ridge of high pressure.
JTWC issued the first warning on TD-03W at 07/0000 UTC, locating
the ill-defined center about 75 nm east of the northern tip of
Mindanao. The MSW was estimated at only 20 kts, based on satellite
CI estimates of 25 kts, coastal synoptic reports of 10 kts, and a
ship report of 20 kts. By 1800 UTC the depression was centered in the
Leyte Gulf region, and over the next couple of days tracked west-
northwestward across the central Philippines. At 08/1800 UTC, based
on a synoptic analysis, the center was relocated about 73 nm south-
southwest of the previous warning position to a point 160 nm southeast
of San Pablo. At 0000 UTC on 9 May the depression's center was in the
Sulu Sea, and by 1200 UTC had emerged into the South China Sea proper.
During its trek across the Philippines the MSW remained set at 25 kts,
though on an occasion or two CI estimates of 30 kts were received.
The winds were upped to 30 kts at 09/0600 UTC when TD-03W's center
was emerging into the South China Sea about 170 nm south-southwest of
Manila. After moving out into the South China Sea, the system turned
northward off the west coast of Luzon. CI estimates had reached 35 kts
at 1800 UTC, but the MSW remained at 30 kts for that warning. However,
at 0000 UTC on the 10th, JTWC upgraded TD-03W to a tropical storm with
35-kt winds (based on CIs of 35 and 45 kts) located 125 nm west-
southwest of Manila. Also at 10/0600 UTC, PAGASA issued their first
warning on the system as a tropical depression, naming it Crising (a
Filipino nickname). It is very interesting that PAGASA didn't initiate
warnings on 03W/Crising until it had reached tropical storm intensity
per JTWC analysis, especially considering that it had trekked across
the central part of the archipelago. Normally, with systems in the
vicinity of the Philippines, PAGASA is the first agency to issue
bulletins. JMA upgraded 03W/Crising to a tropical depression at
10/0600 UTC.
B. Track and Intensity History
------------------------------
JTWC increased the MSW to 40 kts at 10/1200 UTC, but the intensity
held steady at that level for 24 hours. Tropical Storm 03W/Crising
moved slowly northward roughly 100 nm off the west coast of Luzon
for about 36 hours until it turned more to the north-northeast at
11/1200 UTC. PAGASA and JMA upgraded the system to a tropical storm
at 11/0000 UTC with JMA assigning the name Cimaron. The newly-named
storm was then located about 70 nm west of Lingayen. Satellite-derived
CI estimates had reached 45 kts, but based on synoptic reports, JTWC
held the MSW to 40 kts; JMA and PAGASA were estimating 35-kt 10-min
avg winds. At 1200 UTC on the 11th JTWC increased the MSW estimate
to 45 kts; at 1800 UTC the center was relocated slightly to the south
of the 1200 UTC position and was moving slowly north-northeastward.
By 12/0000 UTC Tropical Storm Cimaron/Crising was located about
85 nm north-northwest of Port San Esteban and moving to the northeast
at 4 kts. The storm appeared to have weakened some over the previous
twelve hours due to increased vertical shear. Water vapor imagery
showed the system to be interacting with a frontal boundary, and the
cyclone was located poleward of an upper-level ridge axis in a region
of moderate to strong vertical shear. At 0600 UTC JTWC decreased the
MSW to 40 kts, based on CIs of 30 and 45 kts. By 1200 UTC the storm's
center was about 105 nm north-northwest of Port San Vicente and moving
northeastward at a slightly faster pace (12 kts). The weakening
trend noted earlier proved to be temporary and at 1800 UTC the winds
were increased once more to 45 kts with the storm in the Bashi Channel
about 30 nm west of Itbayat Island. However, Cimaron was already
beginning to show the first hints of what turned out to be a slow,
prolonged transition into an extratropical cyclone.
As Cimaron continued to slowly accelerate northeastward, passing
a short distance southeast of the southern tip of Taiwan and into the
southern Ryukyus, it continued to increase in intensity, reaching a
peak of 60 kts at 1800 UTC on 13 May when it was centered about 25 nm
south-southwest of Miyakojima Island. Vertical shear had weakened
slightly and an upper-level jet stream to the north of the cyclone had
helped to create an outflow channel to the northeast of the center.
Cimaron was being steered northeastward by a low- to mid-level ridge
to the southeast, and its forward motion gradually accelerated with
the approach of a mid-latitude trough from the northwest.
The cyclone was located about 80 nm southwest of Naha, Okinawa, at
0000 UTC on 14 May, moving northeastward at 17 kts. The estimated MSW
was down slightly to 55 kts (based on CIs of 55 and 65 kts), and the
convection was beginning to decouple from the LLCC with a partially-
exposed center evident about 15 nm southwest of the deepest convection.
The center of Cimaron passed over Okinawa around 14/0600 UTC with peak
winds estimated at 45 kts, and by 1200 UTC the storm had become extra-
tropical about 115 nm northeast of the island. The remnants of former
Tropical Storm Cimaron continued as an extratropical gale for another
week, initially moving east-northeastward through 17 May, then curving
more to the northeast, reaching the vicinity of 160E by 19/0000 UTC.
Thereafter, the LOW turned generally northward and moved slowly up
the 160th meridian, being last mentioned (in JMA High Seas bulletins)
as a separate entity at 21/0000 UTC near 45N, 158E.
C. Meteorological Aspects
-------------------------
As stated in the discussion above, JTWC intensity estimates were
frequently based in part on synoptic reports from the Philippines and
ships, but the details of those were not given. At the time Cimaron
reached its peak intensity of 60 kts, Miyakojima Island (WMO 47927),
located about 25 nm to the northeast of the center, reported a 1-min
avg sustained wind of 39 kts. As the cyclone crossed Okinawa, Naha
Airport (WMO 47936) reported a maximum 10-min mean wind of 30 kts.
(The MSW at that time was estimated at 45 kts by both JTWC and JMA.)
As Tropical Storm Cimaron/Crising passed near northwestern Luzon,
Basco recorded 305 mm of rain in 48 hours (the monthly average is
129 mm). Also, Lan Yu, a small island located off Taiwan's south-
eastern coast, recorded 262 mm of rain in 48 hours. (At 13/0000 UTC
Cimaron's center was about 36 nm south-southeast of Lan Yu.) These
rainfall observations were forwarded to the author by Patrick Hoareau;
a special thanks to Patrick for sending them. Unfortunately, the
exact dates/times of the relevant 48-hour periods are not available.
D. Comparisons between JTWC and Other Centers
---------------------------------------------
As noted above, Cimaron was one of the rare cases where JTWC "jumped
the gun" on PAGASA as far as initiating tropical depression warnings
was concerned. However, after PAGASA and JMA had begun issuing
warnings on the system, the estimated intensities by those agencies
compared rather well with JTWC's MSW. JMA's bulletins did not reflect
the slight weakening reported by JTWC on 12 May, but the peak winds
reported by the two centers--60 kts from JTWC and 50 kts (10-min avg)
from JMA--were in excellent agreement. During the system's early
stages as a tropical storm, there were some differences in center
position estimates between the various agencies' warnings, but from
11/1200 UTC onward the coordinates were in remarkably good agreement.
E. Damage and Casualties
------------------------
In spite of the heavy rainfall (and likely associated flooding)
reported on northern Luzon, the author has been unable to locate any
reports of significant damage or fatalities resulting from Tropical
Storm Cimaron/Crising.
***********************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for May: 1 tropical cyclone of hurricane intensity
NOTE: The tracking and intensity information for North Indian Ocean
Basin tropical cyclones is based primarily upon operational warnings
from the Joint Typhoon Warning Center of the U. S. Air Force and Navy
(JTWC) at Pearl Harbor, Hawaii. Occasionally some information may
be gleaned from the daily Tropical Weather Outlooks and other bulletins
issued by the Indian Meteorological Department (IMD), which is the
WMO's RSMC for the basin.
The MSW are based on a 1-min averaging period, which is used by
all U. S. civilian and military weather services for tropical cyclone
warnings. For synoptic observations in the North Indian region,
both 10-min and 3-min average winds are employed, but IMD makes no
attempt to modify the Dvorak scale for estimating tropical cyclone
intensity; hence, a 1-min avg MSW is implied. In the North Indian
basin JTWC usually does not initiate warnings until a system is
well-organized and likely to attain tropical storm status within
48 hours.
North Indian Ocean Tropical Activity for May
--------------------------------------------
The first officially-declared tropical cyclone of 2001 in the North
Indian Ocean basin developed in May in the Arabian Sea off the west
coast of India and became one of the most, if not the most, intense
cyclones on record in that region. Fortunately, the cyclone remained
at sea and eventually weakened, sparing India what could have been a
great disaster. In addition to writing the summary for Hurricane
Adolph, John Wallace also wrote the summary for Tropical Cyclone 01A,
and again, a big thanks to John for his help. (See the March and April
summaries for discussions of two weaker systems which Roger Edson feels
qualified as tropical storms in the eastern Bay of Bengal.)
Tropical Cyclone (TC-01A)
21 - 28 May
--------------------------
A. Origins
----------
The origin of TC-O1A can be traced back to a disturbance in the
western Arabian Sea that was apparently first noticed on 18 May.
A Tropical Weather Advisory issued at 1800 UTC on 19 May centered the
disturbance east of the Yemeni island of Socotra and mentioned that
it was quasi-stationary. Though it generated strong convection, the
disturbance was amorphous with no closed circulation. There seemed
to be no reason to suspect that it had anything other than meager
prospects for development.
On the 20th the situation improved for the disturbance, initially
situated southwest of an upper-level trough, as an upper-level
anticyclone developed over the system, providing good outflow. Though
there was still no synoptic evidence of a closed circulation, there
were the first definite hints of cyclonic structure in satellite
imagery. The disturbance began a slow eastward track.
By 1800 UTC on the 21st, the JTWC Tropical Weather Advisory
indicated that a closed mid-level circulation had developed as the
disturbance turned slightly north of east. Convection remained strong,
and the disturbance's satellite presentation continued to improve.
A surface circulation began to develop, and the JTWC issued a Formation
Alert for the LOW at 0730 UTC on 21 May; the IMD first took notice of
the disturbance at roughly the same time. The JTWC issued the first
warning on Tropical Cyclone 01A at 1800 UTC on 21 May when it was
located about 350 nm south-southwest of Mumbai (Bombay). Convective
banding was developing in the cyclone's western semicircle and the
system's organization was impressive. Located in a highly favorable
environment, the stage seemed set for significant strengthening. Such
was the case.
B. Track and Intensity History
------------------------------
Intensification was initially rapid; TC-01A reached an intensity of
65-kts (1-min avg) at 1200 UTC on 22 May, just 18 hours after its
upgrade, while located roughly 280 nm south-southwest of Mumbai. An
incipient 12-nm eye was apparent in satellite imagery as early as
0600 UTC on the 22nd, twelve hours after its upgrade. Once the MSW
reached 65 kts, the intensification rate slowed considerably, though
it remained steady. This development coincided with the establishment
of a ridge over southern India, which provided a southerly steering
current. The northward turn was much more abrupt than forecast,
sparing west India from a potential disaster. Storm force winds
remained offshore as TC-01A briefly paralleled the coast. At 0000 UTC
on the 23rd, the cyclone began a northwestward turn under the influence
of another mid-level ridge centered over the northern Arabian Sea. By
this time TC-01A had developed impressive outflow and intensification
continued.
The MSW reached an estimated 100 kts at 0000 UTC on 24 May, making
TC-01A only the fourth Arabian Sea cyclone to reach that strength since
1975. It is worth noting that three of these four cyclones have formed
since 1998. Tropical Cyclone 01A attained a peak MSW of 115 kts at
0600 UTC on 24 May while centered roughly 250 nm west-southwest of
Mumbai. This makes TC-01A the strongest Arabian Sea cyclone since at
least 1975. (NOTE: It's possible that the peak estimated MSW will be
decreased to 110 kts in the JTWC's final best track, which would only
tie the previous records.) The JTWC has traditionally applied the same
scale used for Northwest Pacific tropical cyclones to North Indian
Ocean cyclones; using this same wind-pressure relationship results in
an estimated CP of 916 mb for TC-01A at peak intensity. However, this
is pure conjecture; it's clear that the MSW is of primary importance
in Dvorak analysis.
The cyclone maintained its peak MSW for 18 hours; during this time
the system presented a formidable satellite appearance, with an eye
that was initially well-defined. However, the eye soon became
indistinct as conditions became suddenly hostile. Easterly winds south
of the upper-level ridge axis, in conflict with low- to mid-level
westerlies, created substantial shear which began to rend the cyclone
apart; its circulation was distorted and its convection weakened. This
set the pattern that would continue for the rest of TC-01A's duration.
Its forward speed decreased, and the cyclone became quasi-stationary on
the 25th; a slow northward track commenced at roughly 1200 UTC on
26 May under the influence of a low- to mid-level ridge over India.
Tropical Cyclone 01A weakened rapidly beginning at 0000 UTC on the
25th with the MSW dropping below 100 kts at 0600 UTC. At 0600 UTC on
26 May, just 24 hours later, it weakened to tropical storm strength
while located about 300 nm west-southwest of Mumbai or 475 nm south-
southeast of Karachi, Pakistan. The weakening trend slowed thereafter
but did not stop. The final advisory on the cyclone was issued at
1800 UTC on 28 May with the center located some 175 nm west-northwest
of Veraval. By this time TC-01A was a spiral of low clouds, devoid of
deep convection. The cyclone's remnants made landfall in Gujarat on
the 29th; unfortunately, no weather observations from the area were
available to the author.
C. Damage and Casualties
------------------------
The weakening and dissipation of Tropical Cyclone 01A came as a
godsend to the province of Gujarat, still reeling from a deadly earth-
quake in January. On top of that, local news agencies indicated that
some communities were still living in the shadow of damage from 1998's
TC-03A. That being said, the national and local governments mounted
extensive and swift preparations for TC-01A's possible landfall.
Kandla Port, one of the busiest in India, was closed for about four
days. As many as 118,000 people were evacuated from coastal regions
in India while another 50,000 were evacuated from high-risk areas of
Pakistan.
Casualty and damage information for the cyclone is either sparse
or vague. Two hundred houses were washed away in two coastal villages
on the 24th at Kosamba in the Valsad district. This is the only known
damage on land. As for casualties, anywhere from 120 to as many as
900 fishermen were declared missing on the 24th according to local
news reports.
***********************************************************************
SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E
Activity for May: No tropical cyclones
***********************************************************************
NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E
Activity for May: No tropical cyclones
***********************************************************************
NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E
Activity for May: No tropical cyclones
***********************************************************************
SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E
Activity for May: 2 tropical depressions **
** - Both systems were hybrid, cold-cored systems rather than true
tropical depressions.
Most of the information presented below was taken from the
operational warnings and advisories issued by the Fiji TCWC at Nadi.
References to sustained winds imply a 10-minute averaging period
unless otherwise noted.
South Pacific Tropical Activity for May
---------------------------------------
No named tropical cyclones formed in the South Pacific during May,
but gale warnings were issued on two depressions, neither of which were
tropical in nature, but rather were cold-cored, hybrid-type systems
forming under strong shear aloft. The forecast gales were expected
to develop in the systems' southern semicircles due to gradient
compression as the LOWs moved into a strong ridge to the south. The
first depression (14F) formed on 1 May about 225 nm west-northwest of
Rarotonga, initially moved eastward, passing about 50 nm north of the
island around 01/1800 UTC, and later accelerated off to the southeast.
The final warning available to the author, issued by Wellington at
03/1200 UTC, placed the center about 550 nm southeast of Tahiti. The
second depression (15F) formed on 7 May about 250 nm west-southwest of
Tahiti, moved initially southward, then southeastward with the final
warning issued by Fiji, at 09/1200 UTC, placing the center roughly
400 nm south-southwest of Tahiti.
***********************************************************************
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, but since the May, 2001
summary is shorter than average, I've appended the Glossary to the
end following the Author's Note.
***********************************************************************
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
May as an example: may01.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: may01.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.com> OR http://www.geocities.com/taifun00/>
http://www.hurricanealley.net/>
http://www.qisfl.net/home/hurricanemike>
http://www.met.fsu.edu/gsc/Docs/Grads/henning/cyclones/>
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 (1999-2000 season for 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)
***********************************************************************
***********************************************************************
GLOSSARY of ABBREVIATIONS and ACRONYMS
AOML/HRD - Atlantic Oceanographic and Meteorological Laboratory/
Hurricane Research Division, located on Virginia Key, Miami,
Florida, U.S.A.
AOR - area of responsibility
CDO - central dense overcast
CI - current intensity
CIMSS - Cooperative Institute for Meteorological Satellite Studies
(University of Wisconsin-Madison)
CP - central pressure
CPHC - Central Pacific Hurricane Center, Honolulu, Hawaii, U.S.A.
FLW - flight level wind (or winds)
FTP - file transfer protocol
HPC - Hydrometeorological Prediction Center, Camp Springs,
Maryland
IMD - India Meteorological Department (RSMC New Delhi, India)
JMA - Japanese Meteorological Agency (RSMC Tokyo, Japan)
JTWC - Joint Typhoon Warning Center, formerly on Guam, now at
Pearl Harbor, Hawaii
kt - knot = 1 nautical mile per hour
LLCC - low-level circulation center
m - meter, or metre
mb - millibar, numerically equivalent to hectopascal (hPa)
MFR - Meteo France on Reunion Island
mm - millimeter
MSW - maximum sustained wind(s) (either 1-min avg or 10-min avg)
nm - nautical mile = 6076.12 feet or 1852.0 meters
NPMOC - Naval Pacific Meteorological and Oceanographic Center, Pearl
Harbor, Hawaii, U.S.A.
PAGASA - Philippines' Atmospheric, Geophysical & Astronomical Services
Administration
RSMC - Regional Specialized Meteorological Centre
SST - sea surface temperature
STS - severe tropical storm (MSW greater than 47 kts)
STWO - Significant Tropical Weather Outlook - bulletin issued
daily by JTWC giving information about various areas of
disturbed weather and the potential for tropical cyclone
development
TC - tropical cyclone
TCFA - Tropical Cyclone Formation Alert - issued by JTWC when a
tropical cyclone is expected to develop within the next
24 hours
TCWC - Tropical Cyclone Warning Centre (generic term)
TD - tropical depression
TPC/NHC - Tropical Prediction Center/National Hurricane Center, Miami,
Florida, U.S.A.
TS - tropical storm
WMO - World Meteorological Organization, headquartered at Geneva,
Switzerland
UTC - Universal Time Coordinated, equivalent to Greenwich Mean Time
or Zulu (Z)
|
Document: summ0105.htm
Updated: 29th December 2006 |
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