[Index]
Monthly Global Tropical Cyclone Summary January 2000
[Summaries and Track Data] [Prepared by Gary Padgett]
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Monthly Global Tropical Cyclone Summary January 2000 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
JANUARY, 2000
(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 by the AUTHOR
I have been cranking out these summaries now for slightly over two
years, and from the beginning I have been overwhelmed by the reception
they have gotten from the tropical cyclone community--not only from
professional forecasters and researchers, but from those involved in
catastrophe modelling, insurance risk studies, emergency management,
etc, who have found material in the summaries useful to them, and also
from those who just have a keen interest in studying and following
tropical cyclones as a hobby. The time involved, however, spent in
constantly monitoring tropical cyclones, downloading warnings, and
preparing and proofreading the summaries is quite substantial; and,
considering that I have a long commute to work and am away from home
twelve hours every day, the task of writing the summaries becomes very
burdensome at times, especially during busy months.
In an attempt to continue keeping the summaries coming in the form
to which readers have become accustomed, I have enlisted the assistance
of some fellows in various countries who, like myself, have studied and
followed tropical cyclones for years and have a great interest in the
storms. A couple of guys, Matthew Saxby in Australia and Michael V.
Padua in the Philippines, limit their work to sending me tracking
information already typed in columnar format (which can require a
substantial effort in some months). Others, namely Patrick Hoareau
in France, Carl Smith in Australia, and John Wallace in Texas have
actually written some of the narratives for certain tropical cyclones
in recent months. Carl is currently writing reports for cyclones in
the Australian Region, and Patrick plans to assist with the North
Indian Ocean and at least some of the Northwest Pacific typhoons; and
if time permits, John Wallace will write the narrative sections for
Northeast Pacific tropical cyclones. Also, it should be mentioned
that Alipate Waqaicelua, Chief Forecaster of the Nadi, Fiji, Tropical
Cyclone Warning Centre sends me summaries and tracks for most South
Pacific tropical cyclones. I am very grateful to all these gentlemen
for their assistance (and also to many others who send me various
bits and pieces of information about tropical cyclones and their
effects).
That being said, it should be emphasized that I do carefully read
their contributions and edit as I see fit. Each one has his own
writing style with emphases on particular things, and I want their
individual personalities to shine through--in other words, I don't
want to edit and revise to the point everything sounds as if I had
written it. But I do try to insure that there is some consistency
and that the basic things I've always covered remain. No statement
gets through into the final product that I personally object to.
One other issue I'd like to address. The Atlantic and Northeast
Pacific basins are the only areas which essentially have only one
major TCWC issuing advisories/warnings. In all the other basins JTWC
issues official warnings for the U. S. Military Services and for the
benefit of any other parties who wish to use them. Also, with the
exception of the Australian Region, in the other basins there are
national meteorological services which issue warnings in addition to
the official RSMC and JTWC. From the beginning I have made
occasional comparisons between warnings from different warning agencies
when there were significant differences in position and/or intensity.
Analysis of tropical cyclone center positions and intensity by remote
sensing (satellite imagery) is often difficult and very subjective.
It is far from being an exact science. But I have always tried to
be objective in pointing out these to-be-expected discrepancies such
that there is no implied criticism of one TCWC over another, and this
rule likewise applies to any narratives written by my assistants.
***********************************************************************
JANUARY HIGHLIGHTS
--> Intense cyclone threatens Southwest Indian Ocean islands
--> South Pacific sees first cyclones of season
***********************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for January: No tropical cyclones
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NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for January: No tropical cyclones
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NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for January: No tropical cyclones
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NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for January: No tropical cyclones
***********************************************************************
SOUTH INDIAN OCEAN (SIO) - South Indian Ocean West of Longitude 90E
Activity for January: 1 tropical disturbance
1 tropical depression (from December)
1 tropical cyclone
1 intense tropical cyclone
The primary sources of information upon which the narrative is based
are the warnings issued by the TCWC on La Reunion Island, associated
with Meteo France, and which is the RSMC for the South Indian Ocean
basin. However, cyclones in this region are named by the sub-regional
centres on Mauritius and Madagascar with longitude 55E as the dividing
line between their respective areas. La Reunion only advises these
centres regarding the intensity of tropical systems. References to
sustained winds should be understood as meaning a 10-min averaging
period unless otherwise stated. In the accompanying track file
some position comparisons have been made with JTWC's positions, and
warnings from JTWC were used as a source of 1-min avg MSW estimates.
Also, the comments about satellite imagery and other sources of data
such as SSM/I and TRMM were obtained for the most part from the JTWC
warnings. A special thanks to Philippe Caroff of the La Reunion
TCWC for sending me information on the tropical disturbance #03, and
a special thanks to Patrick Hoareau and Jean Marc de Maroussem for
passing along some observations from Mauritius and Reunion during
the approach of Tropical Cyclone Connie.
South Indian Ocean Activity for January
---------------------------------------
After getting off to a rather late start (in late December), the
tropical cyclone season in the South Indian Ocean became significantly
more active during the month of January. Babiola became the first
actual tropical cyclone (hurricane force) in the region, and Connie
became an intense tropical cyclone and threatened the islands of
Mauritius and La Reunion. As the month opened, Tropical Depression
Astride (formerly a tropical storm) was still present in the
Mozambique Channel. (See the December summary for a full report on
Tropical Storm Astride.)
In addition to Babiola and Connie, disturbed weather persisted in
the Mozambique Channel for a couple of weeks starting just before
mid-month. Meteo France on Reunion Island (MFR) issued a couple of
bulletins on this system on 12 and 13 Jan, numbering it as disturbance
#03. JTWC mentioned the area in its STWOs for a few days, but dropped
it on 16 Jan. Beginning on 22 Jan JTWC once again began mentioning an
area of convection in the Channel with an associated partially-exposed
LLCC. MFR issued a single bulletin at 0600 UTC on 24 Jan, referring
to the disturbance as #03 once more, so apparently there was possibly
some connection between this flare-up and the earlier disturbance.
JTWC continued to monitor the disturbance through 26 Jan when it had
weakened significantly. I have attempted to piece together a track
for this system in the companion tracks file.
Finally, a new disturbance/depression formed at the end of the month
and was christened Tropical Storm Damienne on 1 Feb. A report on the
short-lived Damienne will be included in the February summary.
Tropical Cyclone Babiola (TC-04S / SIO #02)
3 - 12 January
--------------------------------------------
A STWO issued by JTWC on 1 Jan indicated that an area of convection
with an associated very weak LLCC had formed approximately 130 nm
south-southeast of Diego Garcia. Over the next couple of days the
disturbed area drifted eastward and by 3 Jan was located about 650 nm
east-southeast of Diego Garcia. MFR began issuing bulletins on the
developing disturbance at 0600 UTC. Animated visible satellite
imagery and scatterometer data indicated weak vertical shearing over
the disturbance and animated water vapor imagery indicated fair
outflow. JTWC issued the first of three Formation Alerts at 1630 UTC,
noting that there had been a significant increase in the areal coverage
of convection. SSM/I data revealed deep convection developing around
the eastern and southern sides of the LLCC.
JTWC issued a second Formation Alert at 04/1430 UTC and a third one
on 5 Jan at 1430 UTC. The disturbance had continued to drift slowly
eastward (or quite possibly a new center had formed) during this time.
The first JTWC warning, issued at 05/1800 UTC, placed the center of
the system almost 700 nm east-southeast of Diego Garcia and moving
southwestward at 9 kts. The MSW (1-min) was estimated at 35 kts, and
convection was consolidating around the LLCC. The system was forecast
to track southwestward under the influence of a low- to mid-level
subtropical ridge to the south-southeast. MFR upgraded the developing
LOW to a tropical depression six hours later with 30-kt winds (10-min
avg), and Moderate Tropical Storm Babiola was christened at 0600 UTC
on 6 Jan, located about 625 nm east-southeast of Diego Garcia. At
1800 UTC Babiola's intensity was holding steady at 35 kts (45-kts 1-min
avg from JTWC) with the LLCC displaced somewhat to the east-southeast
of the primary convection.
On 7 Jan Babiola continued to move slowly to the southwest and
steadily increased in intensity. MSW estimates from both MFR and JTWC
had reached 55 kts by 1800 UTC. A TRMM pass indicated a significant
convective band extending southeast through north wrapping in toward
the LLCC with animated infrared imagery depicting another band forming
180 nm to the west of the LLCC. Babiola began to accelerate toward
the west-southwest on the 8th and continued to intensify, reaching
cyclone (hurricane) strength at 1200 UTC when centered about 575 nm
south of Diego Garcia. A banding eye became apparent, and Babiola
presented a rather symmetrical appearance in satellite imagery with
an upper-level HIGH over the storm enhancing outflow in all quadrants.
The west-southwestward to southwestward motion continued through
9 Jan with Babiola reaching its peak intensity late on the 9th. 200-mb
analysis showed that the cyclonic circulation extended into the upper
levels with good outflow. At 1800 UTC Babiola displayed a ragged eye
20 nm in diameter with good outflow channels over the western half of
the system. The cyclone was by this time beginning to move south-
southwestward. JTWC's peak MSW (1-min) of 90 kts was reached at
this time, and MFR had upgraded Babiola to its peak intensity of
80 kts at 1200 UTC. This represents a perfect agreement of Babiola's
peak intensity between the two TCWCs, corresponding to a Dvorak scale
rating of T5.0. The minimum CP estimated by MFR was 954 mb.
On 10 Jan Babiola remained intense but began to show signs of
weakening. The storm began to move due southward and reached the
westernmost point of its trajectory around 1200 UTC when it was located
about 250 nm east-southeast of Rodrigues Island (which lies about
315 nm east of Mauritius). Early in the day the eye disappeared and
Babiola began to elongate and merge with a trough moving rapidly
across the South Indian Ocean. By 1800 UTC the storm was tracking
south-southeastward and the MSW was down to 70 kts (65 kts per JTWC).
Babiola was becoming less organized due to northwesterly shear.
The storm continued to weaken on 11 Jan as it continued toward the
south-southeast and experienced strong vertical shear. By 0600 UTC
Babiola was merging with the approaching trough and beginning extra-
tropical transition (this based upon remarks in the 0600 UTC JTWC
warning). Animated satellite imagery and data from a SSM/I pass
showed an exposed LLCC with convection sheared 85 nm to the south
and east. JTWC issued its last warning on Babiola at 0600 UTC on
12 Jan with winds estimated at only 25 kts, but MFR continued gale
warnings for the weakening system through 12/1200 UTC, although the
bulletins indicated that the gales were forecast to be occurring well
away from the center (up to 120 nm) in the southeast quadrant. Early
on the 12th the previously mentioned 500-mb trough was just west of
Babiola and was interacting with the system, which was becoming
extratropical. MFR issued their last bulletin on Babiola at 1800 UTC,
downgrading the system to below gale intensity and locating the center
approximately 800 nm southeast of Rodrigues Island.
Tropical Cyclone Connie (TC-08S / SIO #04)
25 January - 2 February
-------------------------------------------
An area of convection appeared on 24 Jan about 315 nm east of
northern Madagascar. SSM/I data indicated a fully-exposed LLCC with
disorganized convection. The next day the persistent convection had
become more organized and MFR initiated Tropical Disturbance Bulletins
at 0600 UTC for disturbance #04. The rapidly strengthening disturbance
was upgraded to a tropical depression six hours later and to Moderate
Tropical Storm Connie at 1800 UTC with 40-kt winds. Connie was
centered about 325 nm northwest of Mauritius at that time. (JTWC
issued a Formation Alert at 1000 UTC, and their first warning was
issued at 1800 UTC, giving a MSW estimate of 35 kts (1-min).)
Convective organization was increasing in an environment of good
outflow and weak vertical shear. TRMM microwave imagery depicted
banding of deep convection in the northeast through southwest
quadrants. The storm had been quasi-stationary for several hours
but was forecast to track southwestward under the influence of a
mid-level ridge to the south.
Connie, however, remained more or less stationary, and actually
moved (or was relocated) northward a bit on 26 Jan while slowly
strengthening. A TRMM pass at 26/0703 UTC revealed what appeared to
be a 27-nm wide eye. At 1800 UTC Connie's intensity had reached
45 kts (55 kts 1-min avg from JTWC) and was still quasi-stationary
about 380 nm north-northwest of Mauritius. By 0600 UTC on 27 Jan
the by-now severe tropical storm with 60-kt winds was moving south-
eastward at 6 kts. A SSM/I pass at 0141 UTC revealed an irregular
eye 20 nm in diameter with the eyewall surrounding approximately
4/5 of the vortex. Multi-spectral imagery showed a significant
convective band entering the LLCC from the southern half of the
system.
At 1200 UTC Connie's center was about 300 nm north-northwest of
Mauritius and MFR upgraded the storm to cyclone status with 80-kt
MSW. (JTWC's concurrent 1-min avg MSW was 85 kts at the time.)
The eye diameter by this time had shrunk to 11 nm and convective
features were continuing to develop and build in toward the LLCC
from the southeast and northeast. With an upper-level HIGH located
over the cyclone, the outflow continued to improve and Connie began
to strengthen rapidly. By 1800 UTC Connie's well-defined 15-nm wide
eye was located approximately 235 nm northwest of Mauritius and had
moved south at 7 kts over the previous six hours. There was a
surface synoptic report of 10-min avg winds of 31 kts from WMO 61986,
located about 140 nm due east of the cyclone.
Throughout Connie's life center position estimates between JTWC
and MFR were in excellent agreement, and intensity estimates agreed
fairly well except that on 28 and 29 Jan, when the cyclone was at
its peak, there was some divergence of opinion regarding the cyclone's
intensity. At 27/1800 UTC JTWC increased the MSW (1-min) to 115 kts,
which equates to T6.0 on the Dvorak scale. MFR's 10-min MSW estimate
was 90 kts--equivalent to a Dvorak rating of T5.5--and as everyone
in the business knows, a difference in Dvorak analysis of 0.5 T-number
represents good agreement. At 28/0600 UTC JTWC began to gradually
bring down Connie's MSW while MFR's value held steady at 90 kts.
At 1800 UTC Reunion increased its MSW estimate to a peak of 100 kts
(T6.0 on the Dvorak scale) while JTWC had brought its value down to
105 kts (T5.5). Remarks in the JTWC warning indicated that this
was based upon CI estimates of 102 kts and 127 kts (T5.5 and T6.5).
Connie's eye had remained well-defined, but cloud tops had warmed
somewhat over the cyclone's center. MFR maintained the 100-kt
intensity through 29/0600 UTC and then brought the MSW down to 85 kts
at 29/1200 UTC. JTWC's estimates had continued to slowly decline and
had reached 80 kts (1-min) by 1200 UTC. The minimum CP in Connie's
history as estimated by MFR was 928 mb at 28/1800 UTC.
By 0000 UTC on the 29th Connie was centered about 130 nm northwest
of Mauritius. The cyclone was maintaining a 10-nm diameter eye, but
was showing signs of shearing to the south. Water vapor imagery
indicated a weak TUTT to the southwest of the storm which was causing
the increase in vertical shear. By 1800 UTC on 28 Jan Connie was
moving to the southwest on a track which carried it about 100 nm west
of Reunion Island around 1800 UTC on 29 Jan. The MSW was down to
80 kts (both MFR and JTWC) as the eye was no longer apparent and drier
air from the TUTT was being injected into the storm's inflow. At
30/0000 UTC Connie was located approximately 145 nm west-southwest of
Reunion and moving southwest at 11 kts--a motion which had increased
to 18 kts by 0600 UTC. The storm's intensity was down to near minimal
cyclone force by this time, and Connie was beginning to recurve to the
south-southeast.
By 1800 UTC on 30 Jan the storm was moving southward about 265 nm
east of the southern tip of Madagascar with 55-kt winds (60 kts 1-min
avg from JTWC). Earlier in the day a SSM/I pass had indicated a spiral
band of convection to the west of the LLCC, but a TRMM pass at 1331 UTC
indicated only isolated convection to the south of the center and
Connie was forecast to continue weakening. On 31 Jan Connie began to
move in a southeasterly direction, steered by a mid-level subtropical
ridge to the northeast and the approaching trough to the southwest.
The storm, however, held on to its intensity with the MSW remaining
at 55 kts through most of the day. JTWC actually increased its 1-min
avg MSW to 65 kts briefly at 1800 UTC based upon satellite intensity
estimates.
However, any re-intensification was short-lived. Animated visible
imagery early on 1 Feb showed a fully-exposed LLCC with rapidly
weakening convection about 70 nm to the east of the center. Infrared
imagery depicted a rapid warming of cloud tops as well as a significant
decrease in the areal extent of deep convection. MFR issued its final
warning at 01/0000 UTC since Connie appeared to be rapidly losing
strength and was taking on extratropical characteristics. JTWC
continued to track the rapidly weakening storm through 0600 UTC on
2 Feb when the MSW was estimated at only 25 kts and the center was
located about 725 nm south of Reunion Island. SSM/I data indicated
a fully-exposed LLCC with weakening convection displaced about 75 nm
northeast of the center. The remnants of Connie were forecast to
continue moving southeastward and weaken.
Jean Marc de Maroussem, a resident of Mauritius, sent me some
observations he'd made during Connie's closest approach to the island.
The lowest pressure reported by Jean Marc was 1000.6 with several wind
gusts exceeding 55 kts and a peak gust of 65 kts. The average
rainfall for the entire island was about 200 mm--a bit of relief for
the drought-stricken island but not enough.
As far as Reunion Island goes, Patrick Hoareau reported that he'd
been listening to the official radio on the internet and wind gusts
of around 60-80 kts had been reported. Also 16,000 people were
without power. Press reports indicated that Connie was responsible
for two deaths on Reunion. One hundred homes were reportedly
destroyed with at least 600 persons homeless.
***********************************************************************
AUSTRALIAN REGION (AUG) - From Longitude 90E Eastward to Longitude 160E
Activity for January: 2 tropical LOWs
1 hybrid LOW
1 severe tropical cyclone
The primary sources of information for Australian Region tropical
cyclones are the warnings and bulletins issued by the three TCWCs
at Perth, Darwin, and Brisbane. Information gleaned from JTWC's
warnings is used as a supplement for times when it was impossible to
obtain Australian bulletins and for comparison purposes. References
to sustained winds should be understood as being based on a 10-min
averaging period unless otherwise noted.
Matthew Saxby, a tropical cyclone enthusiast from Queanbeyan, New
South Wales, Australia, typed up the tracks for the cyclones and LOWs
in the Australian Region. Also, Carl Smith, another dedicated tropical
cyclone enthusiast from the Gold Coast of Queensland, authored the
narratives for Tropical Cyclones 06S and Kirrily. A very special
thanks to Matthew and Carl for their assistance.
A description of the Australian Cyclone Severity Scale can be found in
Chris Landsea's FAQ on HRD's website:
http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqD.html#D2>
or on Michael Bath's Australian Severe Weather site:
http://australiansevereweather.com/cyclones/history.htm>
Also, I performed some editing on Carl's write-ups. For anyone who is
interested in reading his complete cyclone reports, they are available
at the following URLs:
http://www.ace-net.com.au/~carls/TC(06S)Report.htm>
http://www.ace-net.com.au/~carls/KirrilyReport.htm>
Australian Region Activity for January
--------------------------------------
Tropical cyclone activity in the Australian Region was somewhat on
the quiet side. Only one cyclone--Kirrily--was named, and this was
late in the month in the Southeast Indian Ocean off Western Australia.
Earlier there was a tropical LOW in the same region which persisted for
several days and eventually made landfall in Western Australia. JTWC
issued one warning of 35-kt winds with this system based upon a ship
report. Since Carl submitted a report on this LOW, I have included
it below.
There was a short-lived tropical LOW in the Coral Sea off the coast
of Queensland for which Brisbane issued a few warnings on 10 and 11
Jan. Gale-force winds to 35 kts were forecast for the southern
quadrant of the LOW at one point. There was also a gale center on 12
and 13 Jan well east of Brisbane which moved slowly westward toward
the southern Queensland coast. This system was likely a hybrid or
primarily baroclinic LOW. Tracks are given for these two systems in
the companion cyclone tracks file.
Additionally, there was an interesting example of a so-called
"landphoon"--a tropical LOW whose convective cloud signature seems to
improve even after it has moved over land. In mid-January a very weak
LOW formed near the coast of Western Australia and tracked southward
and inland. The maximum winds and minimum pressure when the system
was just off the coast were about 15-20 kts and 999 mb, respectively.
The cloud signature seemed to improve somewhat as the LOW moved
further inland over the Australian Outback. On Sunday, 16 Jan the
center passed just west of the Giles Meteorological Station (25.0 S,
128.3 E) and radar showed the circulation to be very weak.
Australia is one of the very few places where weak tropical LOWs
can drift inland and "appear" to intensify, even after they have
travelled well inland for a day or two. From a satellite perspective
these systems look like tropical storms, with persistent central
convection and a nice symmetrical pattern of cirrus outflow. It is
very possible that in the middle troposphere the circulation does
indeed intensify somewhat. From the standpoint of process, it seems
as if atmospheric conditions are extremely favorable for tropical
cyclone formation, and they do the best they can with land underneath.
(The above discussion was taken from some correspondence with Mark
Lander of the University of Guam and Andrew Tupper of BoM, Darwin.)
Tropical LOW (TC-06S)
18 - 23 January
----------------------
During the 3rd week of January, 2000, a tropical LOW formed in the
Gulf of Carpentaria, northwest of Weipa on Cape York Peninsula. It
drifted slowly west-northwestward into the Arafura Sea over the next
few days, passing to the north of Arnhem Land and Darwin.
By the 18th it had moved into the Timor Sea. BoM Darwin issued the
first shipping warning at 1200 UTC, indicating that a tropical LOW of
1000 mb was centred within 90 nm of 11.0 S, 127.5 E and moving west at
5 kts. Darwin continued issuing shipping warnings until 19/1200 UTC
when responsibility was handed over to BoM Perth as the system was by
then off the Kimberley Coast near 12.7 S, 125.3 E, moving southwest
at 10 kts.
Over the next couple of days the LOW continued moving southwestward
towards the Pilbara coast. JTWC issued the first TCFA on the 20th;
however, development was generally slower than either JTWC or Perth
expected, with JTWC issuing another TCFA later in the day.
Perth issued the first Tropical Cyclone Advice at 6:50am WST on the
21st (20/2250 UTC), stating that at 6:00am a tropical LOW was located
about 380 km (205 nm) north-northeast of Karratha and moving southwest
at 15 kts. The first cyclone warning was issued by JTWC at 21/0300
UTC, indicating that TC-06S had developed in the southeast Indian Ocean
about 350 nm northeast of Learmonth and was tracking southwestward at
10 kts within the steering flow of a subtropical ridge to the
southeast.
The 1st BoM warning for coastal communities was issued at 3:50pm
WST (0750 UTC) on the 21st for areas between Roebourne and Exmouth.
At 3:00pm (0700 UTC) the LOW with a CP of 1000 mb was estimated to be
about 290 km (155 nm) north-northwest of Karratha and moving south-
southwestward at 10 kts. At 21/0900 UTC JTWC noted that animated
satellite imagery indicated a rapid weakening of TC-06S, and animated
water vapour imagery revealed increasing vertical wind shear to the
southeast due to a mid-latitude trough and associated support of a
strong upper-level jet.
The difficulties JTWC had in tracking this marginal tropical cyclone
were revealed when it was relocated 60 nm to the east-northeast of the
previous warning position at 21/2100 UTC. The warning noted that the
system displayed a fully exposed LLCC with deep convection to the
southwest (based on DMSP night-time visible imagery), and animated
infrared satellite imagery depicted increasing convection over the
previous six hours.
Over the subsequent 24 hours TC-06S continued its west-southwestward
motion towards the Pilbara Coast, slowly deepening to 992 mb, but never
quite reaching tropical cyclone strength according to BoM criteria.
The only significant change was noted in a JTWC warning issued at
22/1500 UTC, which stated that, based on infrared satellite imagery,
the system had taken a turn to the southeast during the previous six
hours, and it appeared that the low/mid-level HIGH over the Western
Plateau had weakened and shifted further east than model guidance had
previously indicated, due primarily to the sudden eastward movement of
a mid-latitude trough which had been quasi-stationary off the southwest
coast of Australia. Water vapour imagery also indicated that the
trough had increased in amplitude.
The BoM issued its final warning on this system at 9:50am WST
(23/0150 UTC) on the 23rd, stating that the tropical LOW with a CP of
992 mb and wind gusts to 40 kts was, at 9:00am WST, estimated to be
about 70 km (40 nm) west-northwest of Port Hedland, moving south-
eastward at 14 kts. JTWC issued its final warning at 23/0300 UTC,
noting that the system was dissipating over land.
NOTE: JTWC only issued one warning (22/0600 UTC) estimating the 1-min
avg MSW at 35 kts. Satellite intensity estimates were 25 kts, but the
remarks indicated that there was a synoptic ship report of 35-kt winds
west of the center.
Severe Tropical Cyclone Kirrily (TC-09S)
25 January - 1 February
-----------------------------------------
A developing 1002-mb tropical LOW in the Indian Ocean southeast of
Christmas Island was first mentioned in an Australian Bureau of
Meteorology (BoM), Perth, shipping warning issued at 2157 UTC on
25 Jan when the LOW was centered about 250 nm southeast of Christmas
Island, moving east-southeastward at 11 kts. JTWC issued a Tropical
Cyclone Formation Alert (TCFA) at 26/2130 UTC with winds estimated to
be 25-30 kts. Satellite imagery at 1730 UTC indicated that a LLCC
was located about 400 nm north-northwest of Exmouth, Western Australia,
moving southeastward at 10 kts. Scatterometer data indicated a well-
defined LLCC associated with the convection and 200-mb analysis
indicated that the convection was slowly moving under the axis of an
upper-level ridge which would be expected to provide good outflow.
University of Wisconsin CIMSS Wind Shear charts also indicated
decreasing vertical shear in the path of the disturbance in the
direction of northwestern Australia.
The first tropical cyclone warning was issued by JTWC for TC-09S
at 27/0900 UTC. MSW (1-min) were estimated at 30 kts and the centre
was placed about 330 nm north-northwest of Learmonth, Western
Australia, moving south at 5 kts. Animated multi-spectral imagery
depicted new convection building over the LLCC and low-level cloud
lines were visible moving in toward the center from the southeast.
A mid-level HIGH situated over southwestern Western Australia was
forecast to build northwestward over the Kimberley region within
36 hours and should cause TC-09S to track initially south-
southeastward, then southwestward.
The LOW was named Kirrily by BoM Perth at 28/0016 UTC. The CP was
given as 985 mb and the 0000 UTC position was about 300 nm northwest
of Exmouth. Kirrily was moving southwestward at 6 kts and was causing
rough to very rough seas with moderate swell and 30-40 kt winds within
100 nm of the centre and winds to 50 kts within 30 nm of the centre.
The first public Tropical Cyclone Update was issued by Perth at 8:45am
WST (0045 UTC) on Friday, 28 Jan, stating that Kirrily, a Category 1
cyclone, was located about 295 nm northwest of Exmouth.
At 28/0600 UTC JTWC placed Kirrily's center about 325 nm northwest
of Exmouth, moving west at 9 kts with 55-kt winds (1-min avg). A TRMM
pass at 0314 UTC indicated that the system was developing an eye and
that convective banding was surrounding about 8/10 of the vortex. BoM
TC Update #2 at 2:30pm WST (0630 UTC) upgraded Kirrily to a
Category 2 cyclone that was moving southwestward at 6 kts. Only one
more public update was issued since it had become clear that Kirrily
posed no real threat to the Western Australian coastline.
At 29/0600 UTC JTWC placed Kirrily's center about 600 nm south-
southeast of Christmas Island, moving southwestward at 10 kts with
MSW (1-min) of 80 kts and sporting a 13-nm wide cloud-filled eye. A
minimum CP of 965 mb was estimated by Perth at 1100 UTC when Kirrily
was located approximately 625 nm south-southeast of Christmas Island.
The BoM warning indicated that winds to 65 kts were likely occurring
within 30 nm of Kirrily's centre.
By 1800 UTC JTWC had decreased its MSW estimate to 70 kts as the
cyclone continued to move to the southwest at 9 kts. Kirrily at this
time was located about 675 nm south of Christmas Island or about
470 nm west of Learmonth. Animated satellite imagery showed weakening
of the system and elongation to the southeast. A 29/1404 UTC SSM/I
pass indicated a very bload LLCC; however, convection was confined to
the very center and there was no longer any evidence of any type of
eye. A 200-mb analysis indicated that the upper-level ridge axis
remained south of the system and an upper-level jet was evident to the
southeast. Kirrily was tracking west-southwestward under the steering
influence of a mid-level subtropical ridge to the south and was moving
into an environment of increasing vertical shear.
Subsequent warnings issued by both centres indicated a continued
weakening trend, with the final BoM shipping warning being issued at
2225 UTC on 31 Jan. The weakening remnants of Tropical Cyclone
Kirrily with a CP of 999 mb were located about 750 nm south of
Christmas Island at 2200 UTC and were moving north-northwestward at
4 kts. Winds were forecast to ease below gale force within the next
three to six hours. The last warning was issued by JTWC at 2100 UTC
on 1 Feb with the MSW (1-min) estimated to be only 25 kts. Infrared
satellite imagery indicated a fully exposed LLCC which was moving
northwestward at 6 kts. The final JTWC warning placed the dissipating
centre about 625 nm west of Learmonth or about 700 nm south-southwest
of Christmas Island.
***********************************************************************
SOUTHWEST PACIFIC (SWP) - South Pacific Ocean East of Longitude 160E
Activity for January: 2 tropical depressions
2 tropical cyclones of storm intensity
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. Also, the basic definition of a cyclone in
WMO Region 5 (Australia and the South Pacific) has the unique
requirement that a depression must have gale-force winds more-or-less
completely surrounding the center before the system is named as a
tropical cyclone. Hence, often gales of 35-40 kts may be present in
one or two quadrants but the system is not considered a tropical
cyclone. Last season Fiji initiated their own numbering scheme for
tropical disturbances (01F, 02F, etc) that form in the Nadi AOR.
Some of the numbered disturbances never warrant depression status.
The reports on Tropical Cyclones Iris and Jo were written by
Alipate Waqaicelua, Chief Forecaster at the Nadi TCWC, with only
minimal editing by myself. A very special thanks to Alipate for
sending me the summaries and the cyclone tracks. I wrote the
discussion on Tropical Depression 08F; also, I added some discussion
about the extreme Dvorak objective T-numbers generated for Tropical
Cyclone Iris.
Southwest Pacific Activity for January
--------------------------------------
January saw the formation of the first two South Pacific tropical
cyclones of the 1999-2000 season. In addition to Tropical Cyclones
Iris and Jo, there were a couple of systems carried in warnings from
Fiji as tropical depressions. One of these, TD-08F, persisted for
several days with associated gale-force winds, so I have included a
separate report on this system below. Another depression, TD-06F,
formed on 3 Jan near Vanuatu and moved slowly east-southeastward over
the next couple of days. The system formed and operated in a sheared
environment which did not allow it to strengthen. The depression
passed south of Fiji and had weakened just east of the Dateline by
6 Jan. A track is included for this system in the companion cyclone
tracks file. (A tropical disturbance numbered 07F was mentioned in
Nadi's Tropical Disturbance Summary on 16 Jan, located well to the
west-southwest of Tahiti. This disturbance subsequently dissipated
without being accorded depression status.)
Tropical Cyclone Iris (TC-05P / TC-05F)
7 - 10 January
----------------------------------------
A disturbance was first identified around 03/0600 UTC just north-
west of Espiritu Santo, in Vanuatu, embedded in a stationary monsoon
trough. The system was located under a moderately sheared environment
aloft, with slightly hostile conditions at lower levels. This
basically denied the system any chances for further development.
For another 36 hours, the system was subjected to shear and diurnal
influence, making it at times extremely difficult to locate the general
centre. However, after 06/0000 UTC, the outflow around the system
improved significantly with convection increasing and getting slightly
more organised. Twenty-four hours later, at 07/0000 UTC, convection
was getting better organised still, with the LLCC gradualy moving under
the western edge of the deep convection. Gale warnings were issued
but for certain sectors only. Overnight the depression, displaying
midget characteristics, intensified further under weakening shear
aloft. A compact CDO had also formed which was now moving southeast
at 5 kts.
The depression continued to develop under favourable conditions, and
at 07/2100 UTC was named Tropical Cyclone Iris while located about
180 nm northwest of Port Vila, moving southeast at 5 kts with an
intensity of 35 kts (10-min avg) and forecast to increase to 40 kts
during the next 6 to 12 hours. The cyclone was anticipated to track
more easterly under a westerly steering current. Six hours later, at
08/0000 UTC, winds around the compact centre were estimated to be about
45 kts. Gales were confined to within 60 nm of the centre. Iris
reached storm intensity at 08/0600 UTC while located about 130 nm
northwest of Port Vila, tracking east-southeastward at 8 kts. The
cyclone moved close to or over the island of Epi overnight, but its
compactness was quite evident as recorded winds over Vila, about 60 nm
due south, were only 15 to 20 kts. No damage reports could be
obtained from Vanuatu, but it is most likely that damage, if any,
would be minimal. This was despite an intensity of 60 kts at its
peak, which occurred around 08/1200 UTC.
Iris gradually accelerated eastward as it left Vanuatu, but always
tracking more and more south of east with time. The system was also
becoming more and more asymmetric as it moved closer to Fiji, evidence
of strengthening shear and environmental influence. After 09/0000 UTC,
the cyclone began its weakening trend. Intensity was down to a gale
18 hours later, at 09/1800 UTC, when it was located about 210 nm west-
southwest of Nadi and moving east-southeastward at 13 kts. After
10/0000 UTC, while only about 120 nm southwest of Nadi, Iris was
shunting east-southeastward at 15 to 20 kts into increasing shear
and cooler waters. The cyclone was downgraded to a depression 48 hours
after it had reached its peak intensity--the final warning placing
the centre on the Dateline about 150 nm southeast of Fiji.
Though it was expected that as the system weakened gales might
expand further out from the centre, only fresh to strong winds and very
rough seas with heavy swells were experienced over the western and
southern parts of Fiji. Once the system was named, the intensity curve
took a rate much steeper than any 'normal' cyclone. This was also the
case during the decay phase, though at a much gentler trend. Damage
in Fiji, if any, would have been either minimal or negligible.
JTWC's positions and 1-min avg MSW estimates agreed very well with
Nadi's for Tropical Cyclone Iris. The peak MSW (1-min) from JTWC
was 65 kts while the peak 10-min avg MSW estimated by Nadi was 60 kts.
However, Iris exhibited some features which hinted that the midget
cyclone could have been far more intense for a brief time than either
warning centre estimated. According to Dr. Mark Lander, T-numbers
obtained with the objective (digital) Dvorak method reached T6.5 or
slightly higher for a 4-hour period on 8 Jan from around 0230 to 0630
UTC. The Dvorak scale equates T6.5 with a MSW (1-min) of 127 kts or
a 10-min avg MSW of 112 kts. A satellite bulletin from JTWC at
08/0625 UTC assigned a T-number of 4.0, but the comments indicated
that there was a great inconsistency between the visible and infrared
methods with an IR-derived T-number of 6.0. These extreme T-numbers
persisted for only a short time, however. By 0915 UTC the eye had
disappeared and a JTWC satellite bulletin indicated that the system
had lost much convection over the past two hours.
Mark Lander further comments that such rapid strengthening followed
by rapid decay seems to be a common occurrence with very small, midget
tropical cyclones. They seem unable to remain at peak intensity for
very long--often for just a few hours--before beginning to fall apart.
Typhoons Ellie (1991) and Virgil (1999) were two recent NWP systems
which behaved the same way as Iris. No one will ever know just how
intense Iris became since the core of the small cyclone did not pass
over any weather station and of course there was no aerial
reconnaissance available.
Tropical Depression (TD-08F)
20 - 26 January
-----------------------------
A tropical disturbance was noted near Apia, Western Samoa, around
0600 UTC on 20 Jan. Over the next few days the system drifted slowly
southwestward and gradually became better organized. By 23/1800 UTC
the disturbance had become sufficently developed to be classed as a
tropical depression with the Fiji TCWC initiating gale warnings and
Tropical Disturbance Advisories. TD-08F was then located between
Fiji and the Kingdom of Tonga and displayed a CDO-type cloud pattern.
However, the system had moved south of the 250-mb subtropical ridge
and was being affected by increasing westerly and northwesterly shear.
The depression recurved to a southeasterly course and passed through
the southern Tongan islands on 24 Jan. At 24/0600 UTC the LLCC was
still exposed and the gale-force winds were confined to the south-
eastern semicircle. Six hours later the LLCC had moved closer to the
CDO feature and the cold cloud tops had increased in areal extent.
By 1800 UTC the LLCC was near the southwestern edge of the deepest
convection which had continued to increase in extent with cooling
cloud tops. The depression seems to have reached its peak organization
about this time but there was still evidence of fairly strong vertical
shearing. Gales were reported to be occurring within 40 nm of the
center from the north around the eastern side into the southwestern
quadrant of the system.
Thereafter the LLCC began to be sheared farther and farther away
from the convection as the depression continued to move southeastward
into a region of increasing vertical shear. By 26/0000 UTC the
system was entering Wellington's AOR, and gales were expanding in
area, indicating that extratropical transition was beginning.
Occasionally, in most tropical cyclone basins, poorly-organized
depressions will be seen with little deep central convection but with
peripheral gales on the poleward side due to a tight pressure gradient
with a neighboring area of high pressure. The basic definition of
a tropical cyclone in WMO Region 5 (Australia and the South Pacific)
contains the requirement that sustained gale-force winds should
surround the center before a developing depression is named as a
tropical cyclone. This criterion was ostensibly added to provide
some objective guidance for weeding out poorly-organized systems which
might contain gale-force winds but which do not have the appearance of
a typical, developing tropical cyclone.
In the case of TD-08F, the gales never surrounded the center, but
they were very close to the center--within 30-40 nm, based upon the
warnings from Nadi. In looking at the depression in some infrared
satellite imagery, to me it appeared to be similar to some sheared,
weak tropical storms which I've seen in the Atlantic; however, I do
not have available any Dvorak ratings on this system from any agency.
To my knowledge, NPMOC at Pearl Harbor did not issue any warnings or
alerts on this depression, which suggests that it was poorly organized
with only a very low potential for development.
Tropical Cyclone Jo (TC-07P / TC-09F)
23 - 28 January
--------------------------------------
A weak disturbance was first identified over the northern parts of
Vanuatu on the 19th, embedded in an active and slow-moving monsoon
trough. On the 20th the disturbance was located to the south of the
250-mb ridge with northwest winds of 40 kts to 55 kts above it.
Strong vertical shear had arrested development, which was also strongly
influenced by diurnal effects. However, atmospheric pressure at the
surface continued to gradually fall, but within a fairly broad area
surrounding the system. At 21/2100 UTC, a LLCC could be located by
satellite about 300 nm northeast of Port Vila in Vanuatu and about
340 nm northwest of Nadi in Fiji; hence, the upgrade to tropical
depression phase. The potential for development into a tropical
cyclone in the next 24 hours was still low as shear was still
significant over the system. However, on the 22nd shear was gradually
decreasing and pressure was also falling at a steeper rate. By the
23rd convection had significantly increased with slight improvement in
organisation. The depression was then located in a relatively weakly
divergent area at 250 mb; hence, at 22/2100 UTC the potential for this
depression to develop into a cyclone in the next 24 hours was assessed
to be moderate to high.
The first Tropical Disturbance Advisory on this system was issued
at 23/0000 UTC when it was centered about 460 nm northwest of Nadi and
expected to drift slowly southeastward. Deep convective tops were
cooling and organisation, as well as outflow, was continually
improving. Aloft, the depression was placed along the subtropical
ridge axis in a very favourable area for further intensification.
Gale warnings were also issued around this time, though over certain
sectors only. Overnight TD-09F continued to develop while moving
slowly southward, with cold spiral bands beginning to wrap around the
LLCC. At 24/0300 UTC the depression was named Tropical Cyclone Jo
with winds of 35 to 40 kts close to the centre, which was located about
240 nm west of Nadi. The cyclone was moving south-southeastward at
about 10 kts.
Tropical Cyclone Jo attained storm-force intensity 15 hours later,
at 24/1800 UTC, with gales spreading to within 80 nm of the centre.
Cold spiral bands were still wrapping tightly around the centre. Warm
air intrusion was quite evident on satellite imagery throughout most of
the life of Jo while inside Nadi's area of responsibility. This, to an
extent, made locating the LLCC a little difficult while also preventing
the system from attaining hurricane intensity. Jo's intensity peaked
around 26/0000 UTC, while it was situated about 350 nm south of Nadi,
with a MSW of 60 kts close to the centre. Gales gradually spread
out from the centre to about 180 nm in the southeast semi-circle and
to 150 nm elsewhere around 26/1200 UTC.
Jo's closest approach to Fiji on its way towards the southeast was
on 24 Jan when the centre was located about 240 nm to the west-
southwest. The system had originally been tracking more south-
southeastward but gradually turned to the southeast under a west to
northwest steering flow on the 25th. With gales fanning out more,
strong 10-minute average winds to 32 kts with gusts to 50 kts were
affecting the western parts of Fiji's largest island, Viti Levu, and
nearby islands to its south. Frequent squally rainbands lashed these
areas from late on the 24th until late on the 26th, inducing flash
flooding. There was no major river flooding reported. On the 25th
a building 500-mb ridge from the east prevented any closer approach of
Jo to Fiji. This ridge was basically responsible for keeping the
cyclone on its southeasterly track, entering Wellington's AOR around
26/1200 UTC. Wellington assumed primary responsibility for warnings
on Jo after this time. Tropical Cyclone Jo was finally declared
extratropical at 28/0600 UTC when located well over 1000 nm east of
New Zealand's North Island and a similar distance southwest of Tahiti.
No damage reports in Fiji have been received as yet. If any become
available later they will be reported in a future summary.
Position and intensity estimates by JTWC compared extremely well
with those from Nadi for Tropical Cyclone Jo. As was the case with
Tropical Cyclone Iris, JTWC's and Nadi's peak 1-min avg and 10-min
avg MSWs were 65 kts and 60 kts, respectively.
***********************************************************************
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 included in the July, 1998 summary.
I will include this glossary from time to time, primarily in "lean"
months without a lot of tropical cyclone activity to cover. But if
anyone missed receiving it and wishes to obtain a copy, send me an
e-mail privately and I'll forward 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
January as an example: jan00.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: jan00.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://australiansevereweather.com/cyclones/>
http://www.geocities.com/capecanaveral/6825>
http://www.hcane.com/tropcl.html>
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
I have discovered that JTWC now has available on its new website
the complete Annual Tropical Cyclone Report for 1997 (1996-1997 season
for the Southern Hemisphere). Also, tracks only for the 1998 tropical
cyclones are currently available.
The URL is: http://199.10.200.33/jtwc.html>
Also, TPC/NHC has available on its webpage nice "technicolor"
tracking charts for the 1999 Atlantic and Eastern North Pacific
tropical cyclones; also, preliminary storm reports for all the 1999
Atlantic and most of the Eastern North Pacific cyclones are now
available.
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: summ0001.htm
Updated: 4th January 2007 |
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