[Index]
Monthly Global Tropical Cyclone Summary April 2000
[Summaries and Track Data] [Prepared by Gary Padgett]
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Monthly Global Tropical Cyclone Summary April 2000 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
APRIL, 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.)
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TROPICAL CYCLONE NAMES FOR 2000
ATLANTIC AND NORTHEAST PACIFIC BASINS
ATLANTIC EASTERN CENTRAL
NORTH PACIFIC NORTH PACIFIC
-----------------------------------------------------------------------
Alberto Leslie Aletta * Miriam Upana
Beryl Michael Bud * Norman Wene
Chris Nadine Carlotta Olivia Alika
Debby Oscar Daniel Paul Ele
Ernesto Patty Emilia Rosa Huko
Florence Rafael Fabio Sergio Ioke
Gordon Sandy Gilma Tara Kika
Helene Tony Hector Vicente Lana
Isaac Valerie Ileana Willa
Joyce William John Xavier
Keith Kristy Yolanda
Lane Zeke
* = name has already been assigned to a tropical cyclone
***********************************************************************
APRIL HIGHLIGHTS
--> Tropical Cyclone Hudah strikes Madagascar and Mozambique
--> Severe Tropical Cyclone Rosita strikes Western Australia
--> Two small midget cyclones form in Coral Sea--one hits Queensland
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ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for April: No tropical cyclones
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NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for April: No tropical cyclones
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NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for April: No tropical cyclones
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NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for April: No tropical cyclones
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SOUTH INDIAN OCEAN (SIO) - South Indian Ocean West of Longitude 90E
Activity for April: 1 moderate tropical storm
1 subtropical cyclone (of at least gale force)
1 intense tropical cyclone (from March)
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 tracks 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.
Much of the material presented on the so-called "subtropical
cyclone" in mid-April was taken from information sent to me by Roger
Edson of the University of Guam. A special thanks to Roger for sending
me the write-up on this very interesting system.
South Indian Ocean Activity for April
-------------------------------------
Intense Tropical Cyclone Hudah, which had formed in March, was the
major tropical cyclone item in the Southwest Indian basin during April.
As the month opened the intense storm was still gathering strength
about 200 nm northeast of Mauritius and made a destructive strike on
northern Madagascar on the 2nd. After weakening to below tropical
cyclone (hurricane) intensity, Hudah made a comeback in the Mozambique
Channel and made a second landfall in northern Mozambique. Around
mid-month minor Tropical Storm Innocente stirred the waters of the
central South Indian Ocean for a few days. Also, during the second
week of April a system developed in the Mozambique Channel and
flirted with the coasts of Mozambique and later Madagascar. This
system was classified as a subtropical cyclone by La Reunion and as a
hybrid, subtropical system by JTWC. However, Roger Edson and Mark
Lander of the University of Guam feel that the system was primarily
a tropical cyclone at its peak. Roger has supplied an alternate
track for the disturbance which is included below along with the
track based upon MFR's warnings.
Tropical Cyclone Hudah (TC-21S / SIO #12)
24 March - 9 April
------------------------------------------
To repeat the opening paragraph of the discussion of Hudah from
the March summary:
Intense Tropical Cyclone Hudah had many affinities with February's
great Tropical Cyclone Leon-Eline. Both formed in the Southeast
Indian Ocean in Perth's AOR, moved on fairly straight westerly tracks
across the entire South Indian, struck Madagascar as intense tropical
cyclones, weakened, then regained intensity in the Mozambique Channel
and made final landfalls in Mozambique. Hudah was smaller in areal
extent than Eline but was considerably more intense at its peak and
at its landfall in Madagascar. However, Hudah did not become as
intense in the Channel as Eline did and was weakening some when it
made landfall in northern Mozambique. These two cyclones represent
what could be regarded as the South Indian Ocean's counterpart to
the Atlantic's famous "Cape Verde hurricanes"--great storms which
form in the eastern reaches of the respective basins and manage to
travel on westerly courses for thousands of miles to wreak havoc on
islands and continents at the western sides of the oceans.
Hudah had formed in late March in the western portion of the
Australian Region and had reached tropical storm intensity just before
crossing longitude 90E into the Southwest Indian basin where it was
promptly named Tropical Storm Hudah by the Mauritius Meteorological
Service. For a detailed discussion of the first week of Hudah's life,
please refer to the March tropical cyclone summary. At 0000 UTC on
1 Apr Hudah was an intense cyclone located about 225 nm northeast of
Mauritius, moving on a westerly track toward a disastrous rendezvous
with Madagascar. La Reunion's (MFR) 10-min avg wind estimate was
100 kts and was increased to 110 kts by 0600 UTC. Dvorak ratings were
a solid T=6.5 and JTWC increased their 1-min MSW estimate to 125 kts
at 1200 UTC. At 1200 UTC the eye of Hudah was 400 nm east of
Antanambe, Madagascar, and moving west-northwestward at 13 kts.
The cyclone reached its peak intensity of 905 mb and 120 kts peak
10-min wind (per MFR's analysis) at 02/0600 UTC. JTWC never assigned
a 1-min MSW greater than 125 kts, but the 120 kts 10-min avg would
equate to a 1-min MSW of 135 kts. Hudah was still a small cyclone
with 50-kt winds only occurring within about 25 nm of the center. A
SSM/I pass depicted a 20-nm wide eye with a concentric eyewall feature.
By 1200 UTC the center was closing in on the coast of Madagascar, being
located only about 85 nm east-southeast of Antalaha. The eye of
intense Tropical Cyclone Hudah made landfall around 1730 UTC on 2 Apr
about 15 nm southeast of Antalaha with winds in the neighborhood of
115-120 kts, gusting much higher. The eye had moved off the northwest
coast of Madagascar by 03/1200 UTC and was located about 35 nm north
of Majunga. The majority of the convection was south of the center,
wrapping into the west quadrant. JTWC was estimating the intensity
at 70 kts, but MFR had dropped their estimate to 40 kts. However, in
the next JTWC warning at 04/0000 UTC the MSW was reported as 45 kts.
Hudah continued to move westward farther out into the Mozambique
Channel and slowly began to regain intensity as deep convection began
to rebuild around the LLCC. By 04/1200 UTC winds had picked up to
50 kts (55-kt MSW from JTWC) and the storm was centered about 105 nm
east-southeast of Nacala, Mozambique, moving westward at 11 kts.
Hudah's forward motion slowed considerably as it neared the coast of
Mozambique. At 05/1200 UTC the center was only about 25 nm east of
Porto de Moma and moving to the west at only 6 kts. JTWC increased
the MSW to 65 kts at 05/0000 UTC and MFR re-upgraded Hudah to tropical
cyclone (hurricane) intensity 24 hours later.
Upper-level diffluence over the cyclone improved on 6 Apr and winds
climbed back up to 80 kts (90 kts MSW from JTWC). The storm's motion
became slow and erratic on the 6th as it drifted generally toward the
south. At 1800 UTC Hudah was centered about 120 nm southeast of
Quelimane and appeared to be tracking south-southeastward at 4 kts.
The cyclone was caught in a weakness in the subtropical ridge created
by a mid-latitude trough just off the coast of South Africa. A
significant banding feature had developed over the western half of the
system and a 06/1807 UTC SSM/I pass indicated an irregular eye 15 nm
in diameter. By 0000 UTC on 7 Apr Hudah was centered about 200 nm
east of Beira and was drifting to the west-southwest at 2 kts. The
mid-latitude trough had decreased in amplitude considerably over the
preceding 12 hours and the subtropical ridge was forecast to build
back over the Channel. At 0600 UTC MFR increased the peak 10-min avg
winds to 85 kts with JTWC upping their MSW estimate to 100 kts. By
this time Hudah had begun to drift very slowly to the north-northwest.
By later on the 7th Hudah was drifting northward with the trough
having tracked eastward and the cyclone coming under the influence
of a HIGH over Africa.
Hudah's pace to the north picked up a bit on 8 Apr as the storm
began to weaken slightly. At 0000 UTC the cyclone was centered about
85 nm east of Quelimane with the intensity having dropped to 80 kts
(10-min avg) and 95 kts (1-min MSW). Animated infrared imagery
showed that the eye had become ragged and cloud-filled. Tropical
Cyclone Hudah made landfall around 0600 UTC near Pebane, Mozambique,
tracking northward at 8 kts. The storm began to weaken rapidly after
making landfall with MFR writing their final warning at 1800 UTC on
the 8th. JTWC issued their final warning at 0600 UTC on 9 Apr, the
system having essentially dissipated, although orographic effects
of the mountains apparently were responsible for some localized,
persistent convection as the remnants drifted northward over north-
eastern Mozambique.
Philippe Caroff and Patrick Hoareau have sent me some observations
made on various islands as Hudah passed by. On 31 Mar Hudah's center
passed about 30 nm south of St. Brandon. A maximum 10-min avg wind
of 39 kts was recorded with peak gusts to 55 kts. The northern edge
of the eyewall was only 15 nm south of the island, implying that the
extent of storm-force (>47 kts) winds was very limited. The cyclone
passed at some distance north of the islands of Rodrigues, Mauritius
and Reunion where peak gusts did not exceed 45 kts. The highest
rainfall totals on Mauritius did not exceed 30 mm. Shortly before
reaching peak intensity Hudah passed only about 15 nm south of Tromelin
where a maximum 10-min avg wind of 68 kts was recorded with the peak
gust reaching 98 kts. (Thanks to Philippe and Patrick for passing
along this information.)
The city of Antalaha on Madagascar where Hudah made landfall was
about 90% destroyed. The death toll was reported at 20 with over
300,000 persons severely affected by the cyclone. The storm destroyed
food storage warehouses, and in Antalaha all wooden homes and buildings
were destroyed and the roofs ripped off most concrete structures.
Telephone and electricity lines were downed and schools and churches
heavily damaged. This region is one of the world's primary vanilla
producing areas, and reports indicated Hudah destroyed approximately
one-half of the vanilla crop. Media reports stated that Hudah was
the worst tropical cyclone to affect the Antalaha region in 20 years.
There was a report from Antalaha of wind gusts to 163 kts. It is
unclear whether this was a reliable measured value or an estimate. If
verified, it would imply peak 10-min avg winds in the range of 115-120
kts and a peak MSW of 130-135 kts at landfall. The effects of Eline,
Gloria, and Hudah have combined to make the 1999-2000 cyclone season
the worst for eastern Madagascar since that of 1993-1994 when Tropical
Cyclones Daisy, Geralda, Litanne, and Nadia all struck the eastern
coast at full cyclone intensity.
The author has received no reports of any damage or casualties
resulting from Hudah's landfall in northern Mozambique. If any become
available later they will be reported in a future summary.
Subtropical Cyclone (SIO #13)
7 - 17 April
------------------------------
An extratropical system moved off the coast of South Africa during
the period 5-7 Apr. A circulation was evident about 325 nm east-
northeast of Durban by 0000 UTC on 7 Apr. Whether or not this
circulation was directly associated with the African extratropical
LOW or already existed in the area along an old shear line isn't
totally clear. The circulation was indirectly part of the old
frontal boundary/extratropical system so was basically classifiable
as a subtropical LOW at this time. Winds perhaps reached 30 kts on
7 and 8 Apr but decreased on the 9th. There was a south to north
surge in low-level winds in excess of 30 kts west of the circulation,
so the 30-kt MSW is an attempt to define the winds in the immediate
vicinity of the LLCC.
The disturbance initially drifted north-northeastward in the
Mozambique Channel, then turned to the north, and by 9 Apr was drifting
north-northwestward toward the Mozambique coast. By this time the LOW
was isolated from any extratropical system, and convection, although
fairly shallow, began to slowly develop near the LLCC. According to
Roger Edson's track (see below) the center of the storm just reached
the coast near Inhambane around 11/1200 UTC with the MSW estimated at
55 kts. MFR initiated warnings on the system at the same time,
calling it a subtropical cyclone with 10-min avg winds of 30 kts.
(Since it was MFR's 13th numbered disturbance of the season, I shall
refer to it as STC-13.) The center seemed to drift north-
northeastward and moved just offshore over the next 24 hours while
showing signs of strengthening. JTWC, while referring to the system
as a hybrid-type LOW, issued the first of three Formation Alerts at
12/0130 UTC, and MFR increased the 10-min wind estimate to 35 kts
at 1200 UTC. In Roger's opinion the LOW reached hurricane force at
12/0000 UTC and peaked at 70 kts 1-min MSW at 1200 UTC. This was
based upon visible, infrared, and TRMM imagery. No warnings on
STC-13 were issued by JTWC but the Formation Alerts indicated that
maximum winds were likely in the 25-30 kt range.
Following its flirtation with the Mozambique coast, STC-13 turned
eastward and began to accelerate slightly as it headed in the direction
of southern Madagascar. By 14/0000 UTC the convection was beginning
to shear off, and MFR decreased the 10-min winds to 30 kts while
Roger's 1-min MSW estimate was down to 45 kts. STC-13 was located
about 250 nm west of Tulear on the southwestern coast of Madagascar
at this time, and subsequently seemed to brush the southwestern tip
of the island and then move on off to the southeast. By 0000 UTC on
the 15th all the convection was gone and the mid-levels were overrun
by extratropical cloudiness. JTWC had issued the third Formation
Alert at 0130 UTC on 14 Apr but cancelled it at 0530 UTC after it
became obvious that the convection was shearing off and STC-13 was
beginning to acquire more extratropical features. Scatterometer data
still showed a circulation on 16 and 17 Apr but this wasn't apparent
in satellite imagery.
It is obvious that there is disagreement among tropical experts as
to how to classify this system. La Reunion and JTWC considered it to
be a subtropical, hybrid-type system, while Roger Edson and Mark Lander
feel that it was a "true blood" tropical cyclone. There is no doubt
that it became isolated from any extratropical system and that it had
at times some convection rather tightly wrapped around an eye-like
feature. The sticking point seems to be the shallowness of the
convection, with cloud top temperatures ranging from only around -45 to
-55 C--considerably warmer than in most conventional tropical cyclones.
I went back and read some of the TPC/NHC discussions on Tropical Storm
Nicole in November, 1998, at the time that system was named. Based
upon the comments and also upon my memory of Nicole's appearance in
satellite imagery at the time as compared with STC-13's appearance,
I think it likely that the two systems were very similar in the degree
and depth of convection. In Nicole's case there was a ship report
of sustained winds to 58 kts about the time that an intermittent
eye appeared in the small CDO. This perhaps might suggest that
STC-13 could have been of a comparable intensity. (In his comments
Roger points out that he had no surface observations upon which to
base his intensity estimates--only infrared imagery, TRMM data, and
scatterometer data.)
Tropical Storm Innocente (TC-26S / SIO #14)
12 - 19 April
--------------------------------------------
Tropical Storm Innocente was a weak, insignificant system which
traversed portions of the central South Indian Ocean for a few days
in the middle of April. An area of convection was located on 9 Apr
generally between Christmas and Cocos Islands within an area of
troughing accompanied by strong convergence. The disturbed weather
moved westward over the next few days and scatterometer data on the
10th revealed a LLCC. By 12 Apr the system was approaching 90E and
convection was still fluctuating near the LLCC. Strong southeasterly
flow was occurring along the southern periphery of the LLCC and the
system was experiencing moderate vertical shear. RSMC La Reunion
(MFR) began issuing bulletins on the LOW as Tropical Disturbance
#14 at 12/1800 UTC. The disturbance by this time had entered the
Southwest Indian basin and was located about 500 nm west of Cocos
Island.
The system continued to move westward over the next couple of days
with some slight strengthening on the 13th. MFR upgraded the
disturbance to a tropical depression at 13/0000 UTC, and a STWO from
JTWC noted that there had been an increase in convective organization.
However, on 14 Apr scatterometer data indicated a broad LLCC which
was fully-exposed with isolated deep convection south of the center.
At 14/0600 UTC MFR relocated the center about 115 nm to the east-
northeast of the previous warning position. Coverage was temporarily
dropped six hours later as the system remained weak and disorganized;
however, bulletins were re-instigated at 0600 UTC on 15 Apr as the
disturbance was showing signs of regeneration. JTWC issued a Formation
Alert at 1000 UTC, noting that there had been a significant increase
in areal coverage of convection and that the LLCC appeared to be
located on the eastern edge of the deep convection. Upper-level
(200-mb) analysis indicated that the system was now located under
a ridge. At 1200 UTC MFR re-upgraded the disturbance to a tropical
depression with 30-kt winds, and at 1800 UTC JTWC initiated warnings on
TC-26S, estimating an initial MSW of 35 kts. The depression by this
time was located about 640 nm southeast of Diego Garcia and was moving
west-southwestward at 10 kts. Organization was still improving with
deep convection wrapping around the LLCC. A 15/2028 UTC TRMM pass
depicted a convective band from southeast to west of the system with
the LLCC located about 15 nm east of the convection. Although under
the upper-level ridge axis, the system was still experiencing some
light to moderate vertical shear.
TC-26S (or SIO #14) continued to move slowly to the west on 16-17
Apr, more or less maintaining its intensity. At 1200 UTC on the 16th
MFR upgraded the depression to Tropical Storm Innocente, but six hours
later downgraded it back to depression status. A SSM/I pass at 17/0310
UTC indicated that the LLCC was beneath the northwestern edge of a
convective band. By 17/1800 UTC the system was located about 600 nm
south-southeast of Diego Garcia, moving west at 5 kts, and had
continued to slowly become better organized. JTWC increased the
MSW estimate to a peak value of 45 kts, and MFR upgraded the depression
back to Tropical Storm Innocente with 10-min avg winds of 35 kts.
Innocente displayed a broad LLCC with a weak band of convection around
the southern side. On 18 Apr the moderate tropical storm moved slowly
on a west-southwesterly course and by late in the day was showing signs
of weakening. At 1800 UTC there was only intermittent convection
blowing up near the center and JTWC decreased their MSW estimate to
35 kts. At 19/0000 UTC MFR downgraded Innocente to a tropical
depression once more, and JTWC issued its final warning at 0600 UTC.
There was no convection associated with the fully-exposed LLCC and
the system had moved south of the subtropical ridge axis and was
experiencing increased vertical shear. MFR wrote their final warning
on Innocente six hours later with the weakening center located about
400 nm east-northeast of Rodrigues Island. The residual LOW remained
for several days with occasional flare-ups of convection but never
showed any signs of redevelopment.
***********************************************************************
AUSTRALIAN REGION (AUG) - From Longitude 90E Eastward to Longitude 160E
Activity for April: 2 tropical LOWs
2 tropical cyclones of storm intensity
2 severe tropical cyclones (hurricanes)
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, sent reports he
had written for some of the cyclones; and Jeff Callaghan of the
Brisbane TCWC sent me a considerable amount of information on Cyclones
Tessi and Vaughan and the two Coral Sea LOWs at the end of the month.
A special thanks to all these folks 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>
on Michael Bath's Australian Severe Weather site:
http://australiansevereweather.com/cyclones/history.htm>
or on the Australian Bureau of Meteorology's official website:
http://www.bom.gov.au/info/cyclone/>
Click on the link 'Cyclone Severity Categories'
Carl Smith has a website on which he has placed his full reports on
the various cyclones in the Australian Region this season, as well as
map animations which he has created for the storms. The URL is:
http://www.ace-net.com.au/~carls/current.htm>
Links to various reports and map animations can be found under the
link 'TC Reports & Map Animations'.
Australian Region Activity for April
------------------------------------
April turned out to be one of the most active months of the 1999 -
2000 season in the Australian Region. Two very intense tropical
cyclones, Paul and Rosita, formed in the Perth AOR with Paul moving
harmlessly out into the Indian Ocean while Rosita made landfall near
Broome as a severe Category 4 cyclone. Very early in the month two
midget cyclones, Tessi and Vaughan, popped up in the Coral Sea and
menaced the Queensland coast with Tessi causing substantial damage
in the Townsville area while Vaughan collapsed and dissipated very
quickly near Cairns. Late in the month and into early May, two
tropical LOWs formed in the Coral Sea, moved eastward into the Fiji
AOR thereby receiving a number from the Nadi TCWC, then returned into
Australian waters and approached the Queensland coast. Since reports
of gales were widespread with these systems, I have given them special
coverage below.
Tropical Cyclone Tessi (TC-22P)
31 March - 2 April
--------------------------------
A STWO issued by JTWC at 0600 UTC on 31 Mar indicated that an area
of convection had formed in the Coral Sea well southeast of New Guinea
or roughly 600 nm east of Cooktown, Queensland, and had persisted for
twelve hours. Animated satellite imagery revealed persistent
convection with some degree of organization. A 31/0000 UTC synoptic
analysis indicated strong gradient flow southwest of the convection
and CIMSS charts indicated low to moderate vertical shear. The
disturbance was given a Fair potential to develop into a significant
tropical cyclone. The Brisbane TCWC also began issuing gale warnings
on the LOW at 31/0600 UTC.
The developing tropical LOW continued to move west-southwestward
toward the Queensland coast throughout 31 Mar, gradually getting better
organized, and was upgraded to Tropical Cyclone Tessi with 40-kt winds
at 0000 UTC on 1 Apr when the center was located approximately 530 nm
east of Cooktown. A convective band had developed over the northeast
quadrant, and a 31/2251 UTC SSM/I pass showed convection wrapping in
toward the LLCC from the southwest. At 1200 UTC both JTWC and
Brisbane were estimating winds at 40 kts and the cyclone's appearance
continue to improve in organization.
Cyclone Tessi continued moving at about 10 kts toward the Queensland
coast and made landfall on 2 Apr around 2030 UTC about 20 nm south of
Lucinda. This storm was a midget cyclone which formed in the low-
level easterlies in the absence of any monsoon westerlies. According
to a report on the storm from Jeff Callaghan of BoM Brisbane, at
2300 UTC on 31 Mar the radius of the 1008-mb isobar was about 165 nm.
Twenty-four hours later the 1008-mb isobar had shrunk to a radius of
80 nm, and by the time of landfall had a radius of only 35 nm, thus
indicating how environmental pressures around the vortex rose as the
cyclone intensified. Tessi formed a small, compact radar eye with a
diameter of about 5.5 nm when it was near the coast around 1800 UTC on
2 Apr. In the cyclone's southern semicircle gales were reported as
far south as Gumlu (about 120 km southeast of Townsville), which would
imply a gale radius of about 100 nm; however, on the northern side
gales extended outward from the center only about 16 nm. At Gumlu an
anemometer failed at 60 kts. (It was a pressure tube anemometer at
a height of 6.5 m above the ground.)
The Australian Institute of Marine Science (AIMS) maintains an AWS
on Magnetic Island (about 15 km or 8 nm northeast of the Townsville
Meteorological Office), and some data from this site was received
later and passed along to me by Jeff. The AWS measured a 10-min avg
easterly wind of 59 kts at 02/1600 UTC which, in conjunction with
some other data, indicates that Tessi's center was about 40 km (22 nm)
from Townsville at its closest approach.
Tessi set several new weather records for the month of April at the
Townsville Meteorological Office: highest wind gust (70 kts), highest
daily rainfall (271.6 mm), and the highest monthly rainfall (539 mm
as of 27 Apr). Normal daily rainfall records are taken from 9AM to
9AM local time; however, 423.4 mm was measured in the 24-hour period
ending at 1AM (local time) on 4 Apr. The maximum wind gust occurred
at 02/1540 UTC when the center of the cyclone was about 33 nm away.
The worst wind damage in settled areas occurred just outside the
eye in the area around Mutarnee, a small village 60 km northwest of
Townsville. Many large trees were uprooted and the roof of a
farmhouse was lifted off, battens and all, and deposited in a cane
field about 60 m away. The most extensive tree damage was farther
east in the normally uninhabited beach areas where some isolated
beach huts were unroofed. The eyewall passed over this uninhabited
area consisting mainly of marsh land. The damage in this vicinity
was confined to the immediate coastal area. Bambaroo, which lies
14 km northwest of Mutarnee and a little farther inland, suffered no
damage. After 2000 UTC the eye began to dissipate quickly and Tessi
was rapidly weakening as the center made landfall.
In the Townsville area the cyclone caused widespread wind damage,
mainly to trees and power lines with about 35,000 persons left without
power. Most structural damage was due to falling trees though there
were isolated reports of roof damage attributed directly to the wind.
Widespread flooding occurred with the associated downpour, and there
was a severe landslide in one of the more affluent residential areas
on Castle Hill. There was also some wave damage with several boats
destroyed.
Warnings from JTWC and Brisbane were in pretty good agreement with
regard to position but not with intensity. As was the case with
Cyclone Steve back in February, JTWC's peak MSW estimate was actually
lower than Brisbane's maximum 10-min avg wind estimate. Brisbane
was reporting 50 kts as the cyclone neared the coast whereas JTWC's
peak MSW estimate was 45 kts. (The 02/1200 UTC JTWC warning did
indicate that at least one Dvorak intensity estimate of 55 kts had
been received.) Again, as with Steve, radar and synoptic observations
along the coast seem to confirm that Tessi was somewhat stronger than
its appearance in satellite imagery suggested.
Tropical Cyclone Vaughan (TC-23P / TD-17F)
28 March - 7 April
-------------------------------------------
Like Tropical Cyclone Tessi, Vaughan was a midget tropical cyclone
which formed in the low-level easterlies in the absence of any monsoon
westerlies. A very broad area of convection had developed northwest
of Fiji by 0600 UTC on 27 Mar near 14S, 172E. Synoptic analysis
indicated a weak LLCC associated with the convection with CIMSS charts
indicating the area was under weak to moderate vertical shear.
Twenty-four hours later the main area of convection was about 300 nm
farther to the west, or about 600 nm west of Fiji. Animated multi-
spectral satellite imagery depicted poorly-organized convection forming
along the tail end of a weak shear line extending from New Caledonia
to Fiji with a weak LLCC centered over Vanuatu. The disturbance was
located under the subtropical ridge axis and a 27/1855 UTC QuikScat
pass showed convergent flow north of the shear line.
Fiji began mentioning the system in their daily Tropical Weather
Summary at 28/1800 UTC, numbering it as Tropical Disturbance 17F.
The area remained quasi-stationary for a couple of days roughly 150 nm
south-southwest of Port Vila in Vanuatu. The STWO issued by JTWC at
29/0600 UTC indicated that convection was still poorly organized and
displaced east of the LLCC which was located within a northwest-
southeast oriented surface trough under moderate vertical shear.
Convection increased some on 30 Mar with a 200-mb analysis indicating
a diffluent region over the area. JTWC upgraded the development
potential to Fair while Nadi classified the system as a tropical
depression and issued three gale warnings, mainly in the anticipation
that gales would develop.
On 1 Apr the depression began to move slowly to the northwest
toward an environment more favorable for intensification. Early on
2 Apr the system showed some signs of weakening and JTWC downgraded
the development potential to Poor. However, by 1800 UTC animated
satellite imagery showed convection rapidly building over the LLCC so
the development potential was once more upgraded to Fair. The Nadi
TCWC issued a new gale warning at 02/2100 UTC with the center of the
depression located on the boundary of the Brisbane AOR. JTWC issued
a Formation Alert at 1930 UTC, noting that the system was quite small
in areal extent (90 nm) with maximum winds estimated at 20-25 kts. A
200-mb analysis indicated that the system was moving under the
subtropical ridge. Brisbane took over warning responsibility as
the depression crossed 160E and forecast gales to 40 kts in the
southern semicircle.
JTWC issued their first warning at 03/0000 UTC with MSW estimated
at 35 kts. TC-23P was a small, symmetrical system with associated
cloud lines moving in toward the center from the northwest. The LOW
continued to display increased convective organization and Brisbane
named the system Tropical Cyclone Vaughan at 1800 UTC with peak 10-min
avg winds estimated at 40 kts. By 04/0000 UTC deep convection had
organized around the LLCC, and Brisbane increased the maximum winds to
50 kts while JTWC's estimated MSW jumped to 55 kts based on current
intensity estimates of 35 and 55 kts. Vaughan at this time was located
about 575 nm east-northeast of Cairns, moving west at 11 kts. In
their 1200 UTC warning JTWC decreased the MSW to 45 kts but Brisbane
maintained Vaughan's intensity at 50 kts. Convection had weakened
significantly earlier but had made a comeback during the previous
six hours.
At 0000 UTC on 5 Apr JTWC further dropped the MSW to 40 kts while
Brisbane increased the 10-min avg estimate to 55 kts! The center of
the cyclone by this time was located about 350 nm east-northeast of
Cairns and moving toward the west-southwest at 10 kts. Animated
infrared imagery indicated that convection was cycling between periods
of intensification and weakening. At 1200 UTC JTWC reported the
MSW at 35 kts while Brisbane maintained Vaughan's intensity at 55 kts.
Animated infrared and microwave imagery indicated that the convection
had essentially dissipated between 0000 and 1200 UTC. Around 1400 UTC
there was a massive blowup of convection over the center with cloud
tops colder than -80 C. Willis Island and Cairns radars showed an
eye developing shortly afterward as did TRMM 85 GHz data from a pass
at 2132 UTC. At 1700 UTC Holmes Reef (WMO 94289) reported gales when
the center was about 80 nm distant. BoM Brisbane thought that Vaughan
was rapidly intensifying to hurricane intensity and upped the 10-min
avg winds to 60 kts at 1800 UTC. JTWC, however, only increased their
1-min avg MSW estimate from 35 to 40 kts. This intensification was
short-lived, however, as the mid-level vortex (which was being steered
by a 500-mb ridge) left the low-level center behind. Vaughan rapidly
collapsed just off the Queensland coast east of Cooktown. The
maximum 10-min avg wind estimate dropped from 55 kts at 06/0100 UTC to
30 kts at 0600 UTC.
While JTWC tracked a low-level center inland through 07/0000 UTC,
information from Jeff Callaghan indicates that coastal observations
showed a 500-mb center southwest of Cairns at 06/1100 UTC while
reports from Bougainville Reef (WMO 95288) placed the low-level center
still out to sea near that station. The JTWC warning issued at
06/1200 UTC mentioned that a 06/1120 UTC SSM/I pass depicted extremely
sparse deep convection with no clearly discernible LLCC.
It is obvious that there were greatly divergent interpretations of
satellite imagery of Tropical Cyclone Vaughan by the different warning
agencies, and by other interested parties. Pete Donaldson, of the
Central Pacific Hurricane Center, sent around a visible satellite
image taken at 04/2130 UTC in which he felt that a small, cloud-filled
eye could be seen near the center of a small CDO, and that this feature
represented the LLCC of Vaughan rather than exposed outside of the CDO.
Roger Edson, however, disagreed with this assessment, stating that he
could not see any sign of an eye in the image in question. Roger
supplied a TRMM 37 GHz image from 04/1300 UTC (courtesy of Jeff
Hawkin's NRL Tropical Page) which showed the center of the circulation
near the edge of a large convective area. Roger contended that the
2130 UTC visible image revealed a partially-exposed LLCC on the
southern edge of the CDO with the same low-level cloud lines seen
consistently throughout the day. One final e-mail from Pete implied
that Mark Lander was in agreement with the assertion that a tiny and
indistinct eye had been visible intermittently from 04/2130 UTC through
at least 05/0332 UTC, but the author personally has not received any
e-mail from Mark concerning this cyclone.
Based upon the intensity estimates from Brisbane and JTWC, it seems
fairly obvious that the Brisbane TCWC must have felt that the center
of Vaughan was imbedded within the CDO while the JTWC analysts
interpreted the imagery more in line with Roger's assessment since
their MSW estimate was lowered during the period in question. Dvorak
numbers from KGWC also indicated a weakening system during this time
frame.
The other instance where JTWC's and Brisbane's intensities were
greatly divergent was the eleventh-hour blowup of convection beginning
around 05/1400 UTC (mentioned above) shortly before the cyclone began
to collapse. A Satellite Bulletin from KGWC at 05/2120 UTC noted that
convection had developed rapidly near the center during the past 4 to
6 hours but the T-number was 2.0. It seems likely that the
appearance of an eye on the Willis Island and Cairns radars (also
mentioned above) was the primary basis for Brisbane's increasing the
intensity of Vaughan to 60 kts.
The author would like to point out that the above discussion of the
varying interpretations of satellite imagery by the warning agencies
involved and by other tropical meteorologists should not be construed
as criticism of any person or warning center, nor as an attempt to
imply who may or may not have been correct in their assessment of
Vaughan's intensity. Rather, my purpose was simply to underscore
the inherent uncertainty often encountered in estimating the intensity
of tropical cyclones by remote sensing, especially with midget cyclones
such as Vaughan (and also Tessi). Perhaps some more studies will be
made of this interesting tropical cyclone in an attempt to better
estimate its actual intensity. If I should receive any further
information on Tropical Cyclone Vaughan, I will report it in a future
summary.
Severe Tropical Cyclone Paul (TC-24S)
13 - 22 April
--------------------------------------
The most intense tropical cyclones in the South Indian Ocean this
season seem to have come in pairs: Leon/Eline and Hudah both formed
in the western portion of the Australian Region and moved on westerly
trajectories for thousands of miles, eventually wreaking much havoc
in Madagascar and Mozambique; John and Rosita formed in the Timor
Sea and struck the Western Australian coastline as intense cyclones;
and Norman and Paul both formed off northwestern Australia, moved
westward out into the Southeast Indian Ocean while attaining great
intensity, and then weakened just shy of reaching the boundary of the
Southwest Indian basin.
A STWO issued by JTWC on 10 Apr at 1800 UTC indicated that an area
of convection had formed about 160 nm west of Darwin (near 12S, 128E).
Animated infrared satellite imagery indicated improving convective
organization, and a QuikScat pass indicated a broad LLCC with a
secondary center over land near 17S, 127E. A 200-mb analysis
indicated a favorable environment for strengthening. By 12 Apr the
area of convection had moved westward over the Timor Sea with deep
convection beginning to wrap into the LLCC. CIMSS analysis indicated
the system was under an upper-level anticyclone with weak vertical
shear and the system was given a Fair potential for development. JTWC
issued a Formation Alert at 1730 UTC. At this time convection was
starting to wrap around the northwest quadrant and maximum winds were
estimated at 25-30 kts.
Both Perth and JTWC initiated warnings on the intensifying system
early on 13 Apr. At 0100 UTC the first shipping warning from Perth
placed the center of the LOW about 500 nm north of Exmouth. The LLCC
was still partially exposed with bands of convection wrapping in from
the west side. The LOW tracked west-southwestward fairly quickly
(at 18 kts) and at 1000 UTC was upgraded to Tropical Cyclone Paul
with 45-kt winds and located about 450 nm north-northwest of Exmouth.
Convection continued to consolidate around the LLCC and by around
14/0000 UTC Perth and JTWC were estimating the MSW at 50 kts (10-min
avg) and 55 kts (1-min avg), respectively. Paul was moving westward
at 13 kts at this time, but the cyclone's motion began to tend more
to the west-northwest with time.
The storm underwent a period of rapid intensification on the 14th
with Perth assessing the peak 10-min avg winds at 70 kts at 1000 UTC,
and JTWC's MSW estimate reached 90 kts at 1200 UTC. A 10-nm diameter
eye had become apparent in infrared imagery by this time. Paul's
center was located approximately 300 nm south-southeast of Christmas
Island at the time it reached severe tropical cyclone (hurricane)
intensity. The intensification trend continued with Paul reaching
its estimated peak intensity of 110 kts (10-min avg) and 125 kts
(1-min avg) around 1000 UTC on 15 Apr. Steered by a strong subtropical
ridge to the south, the cyclone was moving on a west-northwesterly
track at this time and was centered roughly 350 nm east-southeast of
Cocos Island. A SSM/I pass at 15/1108 UTC indicated a well-defined
eye 10-nm in diameter with a banding feature wrapping in toward the
LLCC from the south. At Paul's peak intensity gales extended outward
120 nm to the south and 75 nm elsewhere. The radius of 100-kt winds
was estimated to be 20 nm. The minimum central pressure in the storm's
history per Perth's analysis was 920 mb from 15/1000 UTC through
16/2200 UTC.
Paul maintained its peak intensity through around 2200 UTC on
16 Apr. Even as early as 16/0000 UTC the eye had become cloud-filled
and the cyclone's appearance was less symmetric. By 1200 UTC eye
temperatures had cooled somewhat and cloud tops had warmed. The
storm began to track slightly to the west-southwest as indirect
interaction with Tropical Storm Innocente (TC-26S) southeast of Diego
Garcia had weakened the peripheral ridge situated between the two
systems. Severe Tropical Cyclone Paul passed about 125 nm south of
Cocos Island around 0700 UTC on 17 Apr. Winds were down to 100 kts
at this time (120 kts MSW from JTWC) and the storm began to weaken
fairly quickly thereafter. The JTWC warning at 17/1200 UTC noted
that the intense convection was confined to the northwest quadrant.
By 17/2200 UTC Perth's intensity estimate had dropped to 90 kts.
JTWC reported the MSW at 105 kts at 18/0000 UTC and the warning noted
that SSM/I imagery indicated a very tightly-wrapped LLCC but with
the intense convection limited to the well-defined eyewall. Paul's
forward motion had become quite slow, generally toward the west.
By 19/0000 UTC satellite imagery revealed that the cyclone was becoming
elongated along a northwest-southeast axis. The Perth TCWC dropped
the 10-min avg winds to 55 kts at 1000 UTC and JTWC's MSW estimate
had fallen to 65 kts by 1200 UTC. Paul's center was located about
200 nm southwest of Cocos Island at this time.
The storm continued to steadily deteriorate. A 19/2310 UTC SSM/I
pass depicted a partially-exposed LLCC with weak convection located
south to west of the center. Perth wrote their final shipping warning
at 20/0400 UTC as gales were no longer forecast. JTWC continued to
issue warnings on Paul through 21/1200 UTC. Upper-level south-
easterlies generated by a ridge southwest of Paul continued to displace
convection to the northwest of the LLCC. A TRMM pass at 21/0821 UTC
depicted a broad, exposed LLCC with associated isolated convection
located 45 nm to the east and 130 nm to the northwest of the center.
JTWC's final warning at 1200 UTC placed the weakening center about
335 nm southwest of Cocos Island with 35-kt winds and moving slowly
westward at 5 kts. The remnants of Paul continued to drift westward
across 90E and occasionally some convection would flare up, but the
system never made any serious attempt at re-intensification.
Severe Tropical Cyclone Rosita (TC-27S)
15 - 21 April
----------------------------------------
Back in December Severe Tropical Cyclone John ushered in the
cyclone season in Western Australia with a bang, making landfall
west of Port Hedland near Whim Creek as a Category 5 cyclone on
the Australian Cyclone Scale. In April Cyclone Rosita concluded
the season with only a slightly lesser bang, moving inland near
Broome as a Category 4 cyclone. The Perth TCWC mentioned a tropical
LOW in their daily Tropical Weather Outlook issued at 0400 UTC on
15 April. The weak LOW was located about 360 nm north of Broome.
In their STWO at 1800 UTC, JTWC indicated that convection had persisted
for over twelve hours and that animated water vapor imagery showed
improving outflow. A 15/1008 UTC QuikScat pass revealed a well-defined
LLCC. Perth began issuing regular shipping warnings at 0400 UTC on
the 16th with the LOW's center located about 300 nm to the west of its
position of 24 hours earlier.
The LOW drifted very slowly during the next day or so. At 1600 UTC
Perth relocated the center to about 85 nm southeast of the previous
warning position. JTWC issued a Formation Alert at 17/0000 UTC with
the system exhibiting a partially-exposed LLCC located on the northern
edge of the deep convection. Infrared satellite imagery depicted
steadily improving organization with some deep convection beginning to
wrap into the LLCC from the northwest. The first warning from JTWC
was issued at 0600 UTC for a 35-kt system drifting slowly southward
at 3 kts. Deep convection had increased in areal coverage with two
symmetric areas of convection to the north and south of the LLCC.
Perth upgraded the LOW to Tropical Cyclone Rosita with 45-kt winds
at 17/1000 UTC, placing the center about 275 nm northwest of Broome.
JTWC upped their MSW estimate to 50 kts at 1800 UTC, noting that
Rosita had intensified rapidly and had moved southwestward at 14 kts
during the previous six hours.
After this initial rapid intensification, Rosita's winds reached a
plateau for about a 24-hour period. The cyclone moved very slowly to
the south, later turning to the southeast. Around 18/0600 UTC the
cyclone was moving through a weakness in the subtropical ridge and
still exhibited a partially-exposed LLCC although with good upper-
level outflow. Convection continued to increase in organization around
the LLCC and at 2200 UTC Perth abruptly increased the maximum 10-min
avg wind estimate to 70 kts with Rosita's center located about 135 nm
west-northwest of Broome. JTWC increased their MSW estimate to 90 kts
at 19/0600 UTC with the cyclone now moving east-southeastward at 6 kts.
A 14-nm diameter eye had formed and a 19/0126 UTC SSM/I pass indicated
deep convection within the eyewall.
Severe Tropical Cyclone Rosita reached its peak intensity of 105 kts
(10-min avg) with an attendant CP estimated at 930 mb at 1000 UTC on
19 April when the cyclone's center was only 70 nm west-northwest of
Broome. JTWC assigned a peak MSW (1-min avg) of 125 kts just before
the cyclone made landfall at 1630 UTC about 25 nm south-southwest of
Broome, tracking east-southeastward at 9 kts. A 19/1548 UTC TRMM
pass showed a symmetric eyewall with a banding feature west of the eye.
A loop from the Broome radar indicated a slight decrease in intensity
but very little change in the eyewall structure in the 1-1/2 hours
following landfall. Rosita weakened rapidly following landfall and
Perth issued the last advice at 20/0400 UTC, placing the weakening
system with 35-kt winds about 135 nm southeast of Broome. JTWC
issued its final warning at 0600 UTC, noting that the only deep
convection remaining was confined to a small area just south of the
LLCC. At 0400 UTC on 21 Apr Rosita was a rain-bearing depression
located about 450 nm south of Darwin and moving east-southeastward.
Broome fortunately escaped the worst of Rosita's fury. The maximum
wind gust recorded in the town was 77 kts compared to 130 kts (likely
estimated) near the cyclone's center. Seas off the coast were
mountainous with residents saying they had not seen such conditions
in 14 years. About 250 people were relocated from the Bidyadanga
Community, south of Broome, to Port Hedland. In the Broome area most
power lines were down, and several boats broke loose from their
moorings at the height of the storm. At Broome's only banana
plantation, the crop was almost completely lost with only about 10
plants left out of 18,000. (Most of the information in this paragraph
was taken from an Australian Broadcast Corporation news bulletin and
passed along to the author by Carl Smith.)
Coral Sea Tropical LOWs (TD-21F & TD-20F)
26 April - 2 May & 28 April - 2 May
------------------------------------------
During the final days of April and into early May, two tropical LOWs
(i.e., depressions) performed an interesting dance around the Coral
Sea. Gale-force winds were reported in the southern semicircle of
both systems due to a tight pressure gradient with a HIGH to the south,
but neither acquired the structure of a tropical cyclone. (This was
consistent with satellite intensity estimates from JTWC and KGWC with
a Dvorak T2.0 being the highest rating given to either LOW.) The
lion's share of the information given below on these LOWs was provided
by Jeff Callaghan of the Brisbane TCWC with some supplemental data
from Matthew Saxby of Queanbeyan, NSW. A special thanks to Jeff and
Matthew for sending me the information.
Over the period 26-27 Apr a large 1034-mb HIGH moved into the Tasman
Sea. A marked upper-level trough extended into far northern Queensland
and a small tropical LOW formed under a diffluent wind pattern between
upper northwest winds ahead of the trough and upper-level southeasterly
flow towards New Guinea. The intense pressure gradient between the LOW
and the HIGH generated gales in the Cairns area. The LOW became
quasi-stationary for a time on 27 Apr roughly 150 nm north of Cairns
and became quite deep as a 26/2300 UTC RAWIN showed winds to 52 kts at
850 and 800 mb. Above 600 mb winds turned northwesterly under the
influence of the upper-level trough and convection which had formed
moved off to the southeast, preventing further development. Green
Island AWS (WMO 95289) reported almost continual gales from 26/0530 to
27/1248 UTC with a maximum 10-min wind of 43 kts, and Low Isle AWS
(WMO 94285) reported continual gales from 26/1700 to 27/1100 UTC with
a peak 10-min wind of 41 kts. A trawler with a crew of 3 sank near
Norman Reef northeast of Cairns but the crew was rescued. A family
of 6 was rescued by helicopter from a remote beach 32 km southeast of
Cairns after the heavy seas forced them to beach their power boat. In
addition the chopper crew rescued 13 people from a flooded campground
west of Cairns.
The diffluent pattern east of the upper-level trough which helped to
form the Cairns LOW moved out into the Coral Sea and triggered a mass
of convection. A surface LOW formed to the west of this convection
and by 28/0000 UTC QuikScat data indicated gales under the convection
to the east. The LOW moved towards the southeast as the mid- to
upper-level trough became quite involuted to the south. The LOW
passed to the north of Ile Loop AWS (WMO 91574) where east-southeast
winds of 36 kts were reported at 29/0700 UTC, and later near Ile
Surprise AWS (WMO 91570) where winds reached 32 kts at 1100 UTC. The
lowest pressure of 998.3 mb was recorded at 1600 and 1700 UTC. With
a 1034-mb HIGH centered over Auckland, a huge area of gales and near-
gales were being directed from the Dateline towards the east coast of
Australia. The center of the LOW moved east of 160E after 0000 UTC
on 29 Apr, reaching its easternmost location of 162E between 1200 and
1800 UTC. The TCWC at Nadi, Fiji, issued gale warnings on the system
during this time and numbered it as Tropical Depression 20F.
The cyclonic portion of the mid-level involution began moving north
towards the LOW and the steering mechanism became the deep ridge to
the south, thus turning the LOW westward toward Australia. Some
intensification occurred as the mid-level LOW began to couple up with
the low-level center. The system passed to the north of Cato Island
(WMO 94394) where gales were reported generally between 2000 UTC on
30 Apr and 0200 UTC on 1 May. The peak 10-min avg wind recorded was
44 kts at 30/2300 UTC while the lowest pressure of 999.5 mb occurred
at 01/0200 UTC. The LOW was becoming almost vertically stacked and
was probably near peak intensity as it went past Cato Island. Many
ships reported gales with several reporting 10-min mean winds as high
as 45 kts on 1 May.
Several locations along the Australian coast reported winds in
excess of gale force. The highest 10-min avg wind appears to have been
recorded at Double Island Point AWS (WMO 94584): 43 kts at 01/0351 UTC,
while the highest gust recorded was 57 kts at Cape Moreton AWS (WMO
94594) at 01/0832 UTC. The Toowoomba AWS (WMO 94551), which is
inland, reported mean winds of 33 kts with gusts to 41 kts at 1341 UTC
on the 1st. A visible satellite image of the LOW at 01/0131 UTC shows
an exposed LLCC off the Queensland coast with an extensive area of
lower clouds and fairly shallow convection to the southeast.
Fortunately the LOW made landfall as a weak system and caused little
wind damage and no heavy rain. There was serious beach erosion on
Fraser Island and in the Sunshine and Gold Coast tourist areas. Peak
wave heights of 7.4 m were reported on the Gold Coast and reached
8.1 m and 9.7 m at Tweeds Head and Brisbane, respectively.
Turning back to the Cairns LOW of 26-27 Apr--after the 27th this
first LOW became detached from the surface trough and was tracked as
a vorticity feature on satellite imagery moving initially northwestward
but later turning eastward. QuikScat winds at 29/2007 UTC showed gales
on its southern side with a center near 13S, 153E. The small LOW was
rapidly moving within the deep westerlies north of the deep cyclonic
circulation to its south. It made it as far east as 161E by 2100 UTC
on 30 Apr where Fiji designated it as Tropical Depression 21F. The LOW
then moved around the periphery of the larger circulation and headed
westward toward Australia. Just as the other LOW (TD-20F) was
weakening and crossing the coast, TD-21F replaced it about 110 nm
north of Cato Reef at 02/0000 UTC. The LOW kept the gales going to
the south for another 24 hours before it too made landfall as a weak
system about 80 nm (150 km) north of where the first LOW had landed.
***********************************************************************
SOUTHWEST PACIFIC (SWP) - South Pacific Ocean East of Longitude 160E
Activity for April: 3 tropical depressions
1 tropical cyclone of gale 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 report on Tropical Cyclone Neil was 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 summary and the cyclone's track.
Southwest Pacific Activity for April
------------------------------------
Several tropical systems roamed the waters of the South Pacific east
of 160E during April but most were quite weak. The only named cyclone
was Neil, which formed around mid-month near Fiji and caused some heavy
rains and marginal gales in the islands before moving off to the south-
southeast. A system on 5 and 6 Apr was referred to as a tropical
depression in two Tropical Disturbance Summaries but was not assigned
a number. This depression formed just east of the Dateline east of
Fiji and appeared to have been severely sheared with little real
potential for development. No track is given for this system.
A disturbance formed west of Tahiti from an upper-level cutoff LOW
on 10 Apr and moved west-southwestward for a couple of days. This LOW
was designated 18F but was never referred to as a tropical depression.
Finally, at the end of the month two tropical LOWs (depressions) from
the Australian Region moved eastward across 160E and were numbered 20F
and 21F before moving back westward into Brisbane's AOR. Since the
primary impact of these LOWs was to Australia, they are covered in the
discussion of activity for the Australian Region.
Tropical Cyclone Neil (TC-25P / TC-19F)
15 - 17 April
----------------------------------------
Tropical Cyclone Neil was the sixth cyclone to form in RSMC Nadi's
AOR this season. A disturbance was first identified embedded in a
slow-moving trough of low pressure just northeast of Fiji around
12/1200 UTC. At this stage the trough, along with the disturbance,
was drifting slowly southwestward towards Fiji. After 13/0600 UTC
the system had developed into a tropical depression while located some
60 nm northeast of Vanuabalavu island with convection immediately
around the centre increasing. Though it was then located just south
of the 250-mb ridge, shear was still minimal. Overall organisation
had not changed much by 14/0000 UTC, even though deep convection
appeared weakly sheared to the east. Twenty-four hours later, the
depression had moved further southwest with convection increasing and
becoming better organised around the LLCC. Good outflow in certain
sectors was also established as the system was now located under the
250-mb ridge axis with good diffluent flow over it. A warm SST of
around 30 degrees Celsius certainly enhanced the system's potential
to reach tropical cyclone intensity within the next 24 hours.
At 15/1200 UTC, in the second Tropical Disturbance Advisory issued
by RSMC Nadi, the potential for development to a cyclone within 12
to 24 hours was raised to "high" as all factors became more
favourable, though convection was still undergoing some diurnal
variation. At this time the depression was located about 60 nm
southeast of Kadavu and slow-moving, but anticipated to move further
southwards. Through the early hours of the morning of the 16th,
(Local) the depression further intensified with convective tops
cooling and organisation improving significantly. At 15/1700 UTC,
the depression was named Tropical Cyclone Neil while located some
80 nm southeast of Kadavu and still slow-moving.
Through the 16th (Local), Neil was subjected to increasing westerly
shear as it began to move southward at about 06 kts which effectively
displaced the deep convection about 30 to 40 nm southeast of the LLCC.
Shear was reinforced by a deep 250-mb trough upstream of the cyclone.
After 16/0600 UTC it was apparent that shear over the system was only
going to increase further and that the steering field would move it
rapidly into cooler waters, thus demolishing any organisation that
would have prevailed. Hence, at 16/1200 UTC, the system was
downgraded to a tropical depression with gales confined to within
120 nm of the centre only in the southern semicircle, enhanced by
an intense surface HIGH cell to the south. Former Tropical Cyclone
Neil finally exited Nadi's AOR after 17/1800 UTC as a depression with
gales still confined to the southern semicircle.
Damage attributed to Neil was minimal, with only marginal gales
reported over the two southern-most islands in Fiji: Kadavu and
Ono-i-Lau. Torrential rain was experienced over some parts of Fiji
while strong winds affected most places. There was one fatality
due to drowning, but not directly associated with the cyclone.
***********************************************************************
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
April as an example: apr00.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: apr00.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 website the
complete Annual Tropical Cyclone Report (ATCR) for 1999 (1998-1999
season for the Southern Hemisphere). Also, ATCRs for earlier years
are 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 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)
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Document: summ0004.htm
Updated: 4th January 2007 |
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