[Index]
Monthly Global Tropical Cyclone Summary April 2002
[Summaries and Track Data] [Prepared by Gary Padgett]
| Tropical
Cyclones
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Monthly Global Tropical Cyclone Summary April 2002 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
APRIL, 2002
(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.)
*************************************************************************
APRIL HIGHLIGHTS
--> Quiet month--two cyclones in Southeast Indian Ocean
*************************************************************************
***** Feature of the Month for April *****
ACKNOWLEDGMENT AND THANKS TO MY SUPPORT TEAM
In July of 1999 I was contacted by Patrick Hoareau of Rennes, France,
who had been reading my monthly tropical cyclone summaries and had col-
lected many annual tropical cyclone reports from JTWC, Meteo France, and
perhaps other warning centers. Patrick had compiled some statistics on
Southern Hemisphere tropical cyclones, and was interested in forming an
e-mail group with other interested persons. At the time I was already
in contact with several tropical cyclone enthusiasts, including Matthew
Saxby and Michael Bath in Australia, Michael Padua in the Philippines,
and John Wallace, Eric Blake and Michael Pitt here in the United States.
So we formed an informal e-mail discussion group for the purpose of
sharing information, asking questions, exchanging satellite pictures,
etc. The group has grown now to 21 members, including (in addition to
myself and the ones named above) Carl Smith in Australia, Carl's brother
Phil in Hong Kong, Jean Marc de Maroussem in Mauritius, Huang Chunliang
in China, Bruno Benjamin on Guadeloupe, veteran storm chaser and photo-
grapher Jim Leonard from the Florida Keys, Jim's friend and chase partner
Mike Theiss, Jose Garcia in Puerto Rico, Karl Hoarau in Paris, Karl's
brother Jean Paul on Reunion Island, Jim Edds, another storm chaser and
photographer from the Keys, and Rich Henning, a member of the USAF
Reserves' 53rd Weather Reconnaissance Squadron--The Hurricane Hunters.
Just added a couple days ago was Simon Clarke from Cleveland, Australia.
When things start stirring in the tropics, e-mail traffic among group
members picks up also. Some members contribute only when their primary
basin of interest (usually where they live) is active while others
actively follow tropical cyclones around the globe. Several of them
are prime contributors of information for the summaries and track files
I prepare each month, and I am very grateful to them for the material
they send to me. Most of the members have sent me information at one
time or another which has found its way into the cyclone summaries, and
I always try to acknowledge their contributions. At various times in
the past, Matthew Saxby and Patrick Hoareau sent me tracks for portions
of the Southern Hemisphere basins, and Carl Smith undertook for awhile
to write summaries of the eastern Australian cyclones, but their circum-
stances changed such that it was not feasible for them to continue doing
so. Michael Padua and Huang Chunliang now regularly send me compiled
tracks and intensities from the various Asian warning centers in the
Northwest Pacific basin. I incorporate some of this information into
the monthly cyclone track files, a feature which in my opinion adds
value to the files. Also, recently, Michael Bath has been assisting me
by proofreading some of the individual cyclone narratives.
In addition to these fellows, many professional meteorologists around
the world have contributed inputs into the summaries, and continue to do
so: Jeff Callaghan from Brisbane; Mark Kersemakers, Lori Chappel, Ross
Evans, Geoffrey Garden and Peter Bate at Darwin--maybe others there;
Steve Ready at Wellington; Alipate Waqaicelua at Nadi, Fiji; Philippe
Caroff at La Reunion; Mark Lander and Roger Edson at the University of
Guam; David Roth at HPC; Jack Beven and Eric Blake at TPC/NHC; Tony
Cristaldi of the Melbourne NWS office; Pete Bowyer and Chris Fogarty of
Environment Canada. Alipate Waqaicelua, Chief Forecaster at Nadi, has
been especially helpful as he regularly writes summaries for internal use
of all the named tropical cyclones in Fiji's AOR. Alipate sends these to
me with the permission to use them in my monthly summaries. Also, over
the past year Karl Hoarau has become someone I can rely on to perform
special studies of systems which "fell through the warning crack" but
which warrant some documentation in the summaries.
One member of my informal discussion group needs singling out for
special mention. John Wallace, a student at the University of Texas
in San Antonio, has over the years seriously studied tropical cyclones
much as I did as a teenager, and has developed a special interest in
climatology and patterns of storm formation. John also has a special
interest in the storms of the Northeast Pacific basin and the North
Indian Ocean and has written many of the narratives for cyclones in those
basins for me since late 1999. John's assistance was invaluable during
the very active Northern Hemisphere seasons of 2000 and 2001, during
which I got very much behind schedule. Fortunately, John has agreed
to continue covering the NEP and NIO cyclones this season as time
permits. Needless to say, I am very grateful to John for the assis-
tance he has rendered in the past and for his willingness to continue
in that capacity, so I have decided to accord him co-author status.
No doubt there are others who have contributed information for the
summaries, or else have answered some of my questions, whose names I
can't recall at the moment. To any such persons, as well as all those
I've named above, I would like to extend a very special thanks. And of
course I'm very grateful to Chris Landsea for asking me to undertake the
writing of the summaries in the first place. It has been, and continues
to be, a very rewarding experience. Now that I am retired from my full-
time job and have much more time on my hands, I plan to incorporate some
new features and formats into the summaries and track files which I hope
will be perceived as improvements. But before I change anything I will
announce it in advance and perhaps solicit some opinions regarding the
impact of any proposed changes.
Several of the members of my cyclone chat group have some very nice
websites, and in next month's summary I plan to include a short descrip-
tion of those.
*** Additional Feature ***
NOT QUITE "MED-CANES"
Most tropical cyclone forecasters, researchers, and enthusiasts
nowadays are familiar with the cyclonic storm systems which at rather
infrequent intervals form over the Mediterranean Sea and exhibit satel-
lite signatures which look very much like tropical cyclones, even to the
extent of sometimes having very deep convection with cold cloud tops.
Meteorologists are rather noted for coining names for phenomena which
don't seem to quite fit the standard classification schemes--e.g.,
landspout, gustnado, landphoon, neutercane--and some folks have gotten
into the habit, for better or for worse, of referring to these rare
Mediterranean cyclones as "med-canes". Just as there is no officially
agreed-upon terminology to identify these cyclones, there is no general
consensus as to how they should be classified meteorologically. Some
persons feel that at least some of these storm systems are basically
operating as tropical cyclones; others argue that they should be clas-
sified as subtropical cyclones or some sort of hybrid; and there are
those who feel that they are a warmer-climate cousin of the polar LOWs
of the far North Atlantic.
The purpose of this article, however, is not to discuss "med-canes"
but rather to mention a couple of similar systems which were not located
in the Mediterranean Sea, but were quite close, and to give some links
where images of these and similar systems can be viewed. Back in
February Julian Heming of the UKMET office sent around an image of a
small vortex which had formed off the coast of Morocco. In Julian's
opinion this was some sort of hybrid system, perhaps similar to the
Mediterranean cyclones. An image of this system can be viewed at the
following website:
http://www.metoffice.com/sec2/sec2cyclone/tcimages/Misc/morocco2.gif>
Paul McCrone, Chief Forecaster at the Headquarters of the Air Force
Weather Agency (AFWA), also felt that the system was some sort of hybrid.
Paul has some images of the cyclone archived at the following URL:
http://zephyr.unl.edu/~pmccrone/tropical/2002/med-cane/>
The system was located not a great distance southwest of the Strait of
Gibraltar and exhibited a tight swirl of mainly low clouds with an
eye-like "hole" in the center. (The date and time of the image sent by
Julian was 18 February 2002 at 1400 UTC.)
Julian also sent me an image (no link available) of an interesting
system he'd noted over the Black Sea on 21 March of this year. For a
period of about six hours it seemed to form an eye-like structure before
filling in again. Julian stated that the LOW seemed to have a frontal
structure. It seems likely to me that perhaps this particular system
was somewhat analogous to the LOWs which often form over the Great Lakes
in wintertime and have some characteristics in common with polar LOWs.
Julian has placed some images of several hybrid or otherwise unusual
cyclonic systems at the following URL:
http://www.metoffice.com/sec2/sec2cyclone/tcimages/Misc/>
Included are another similar system off the Moroccan coast, a genuine
"med-cane" in January, 1995, and the South Atlantic tropical storm (or
strong depression) in April, 1991, the latter being the only tropical
cyclone to date known to have formed in the South Atlantic Ocean.
*************************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for April: No tropical cyclones
*************************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for April: No tropical cyclones
*************************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for April: 1 tropical depression
Sources of Information
----------------------
Most of the information presented below is based upon tropical
cyclone warnings and significant tropical weather outlooks issued
by the Joint Typhoon Warning Center of the U. S. Air Force and
Navy (JTWC), located at Pearl Harbor, Hawaii. In the companion
tropical cyclone tracks file, I normally annotate track coordinates
from some of the various Asian warning centers when their center
positions differ from JTWC's by usually 40-50 nm or more. All
references to sustained winds imply a 1-minute averaging period
unless otherwise noted.
Michael V. Padua of Naga City in the Philippines, owner of the
Typhoon 2000 website, normally sends me cyclone tracks based upon
warnings issued by the Japanese Meteorological Agency (JMA) and the
Philippines' Atmospheric, Geophysical & Astronomical Services
Administration (PAGASA). Also, Huang Chunliang of Fuzhou City, China,
sends me each month tracks obtained from warnings issued by the
National Meteorological Center of China (NMCC), the Central Weather
Bureau of Taiwan (CWBT) and the Hong Kong Observatory (HKO). A very
special thanks to Michael and Chunliang for the assistance they so
reliably provide.
In the title line for each storm I have referenced all the cyclone
names/numbers I have available: JTWC's depression number, the
JMA-assigned name (if any), JMA's tropical storm numeric designator,
and PAGASA's name for systems forming in or passing through their
area of warning responsibility.
Northwest Pacific Tropical Activity for April
---------------------------------------------
No named tropical storms formed in the Northwest Pacific basin during
the month of April. One tropical depression formed and was tracked by
JTWC and JMA, being designated as TD-04W by JTWC. The depression began
forming northwest of Pohnpei early in the month, and the first warning
from JTWC at 1800 UTC on 5 April placed the center about 750 nm east of
the southern Marianas Islands. The rather large system had already been
picked up by an approaching trough and was moving rather quickly to the
north-northeast. This north-northeastward motion continued, becoming
more northeasterly and later easterly. The depression was already in
the process of extratropical transition by 0600 UTC on the 6th and JTWC
issued their final warning on the system at 07/0000 UTC, placing the
weakening center approximately 350 nm west-southwest of Wake Island. JMA
continued following the weak, residual LOW through 08/1200 UTC to a
position near Wake Island. During the formative stages of this large
tropical depression, winds gusting to gale force were reported from the
islands of Chuuk and Nukuoro.
*************************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for April: No tropical cyclones
North Indian Ocean Tropical Activity for April
----------------------------------------------
April lies well within the spring transition season when tropical
cyclones often form in the North Indian Ocean. No tropical storms or
well-organized depressions formed in April, 2002, but there was an
interesting disturbance which warrants mention. A weak LLCC with some
associated cycling deep convection formed on 25 April at a very low
latitude (3.5N) about 350 nm off the east coast of Somalia in the western
Arabian Sea. The system's organization continued to improve and at
25/2200 UTC, JTWC issued a TCFA for the LOW. Deep convection had con-
tinued to build near the LLCC and the system presented a fairly well-
organized appearance in visible satellite imagery. JTWC estimated the
maximum winds at 20-25 kts. The disturbance, however, made landfall at
approximately 26/1530 UTC in central Somalia just north of the city of
Hobyo, so the TCFA was cancelled at 26/1900 UTC.
*************************************************************************
SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E
Activity for April: 1 tropical cyclone **
** - visitor from the Australian Region (Dianne-Jery)
Southwest Indian Ocean Tropical Activity for April
--------------------------------------------------
Following a rather active January through March period, no tropical
storms or cyclones formed in the Southwest Indian Ocean during April.
The only storm on the charts was Tropical Cyclone Jery, which had formed
in the Australian Region where it was known as Dianne. Dianne-Jery
remained in the eastern extremity of the basin, later moving back east
of longitude 90E into Perth's AOR once more. The cyclone reached an
estimated peak intensity of 80 kts (10-min avg MSW from MFR), falling
10 kts shy of attaining intense tropical cyclone status. JTWC, however,
did estimate the peak intensity at 105 kts (1-min avg MSW) for one
warning cycle.
*************************************************************************
NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E
Activity for April: 1 tropical cyclone
1 severe tropical cyclone (hurricane)
Sources of Information
----------------------
The primary sources of tracking and intensity information for
Northwest Australia/Southeast Indian Ocean tropical cyclones are
the warnings and advices issued by the Tropical Cyclone Warning
Centres at Perth, Western Australia, and Darwin, Northern Territory.
References to sustained winds imply a 10-minute averaging period
unless otherwise stated.
In the companion tropical cyclone tracks file, I occasionally
annotate positions from warnings issued by the Joint Typhoon Warning
Center (JTWC) of the U. S. Air Force and Navy, located at Pearl
Harbor, Hawaii, when they differ from the Australian centres' coor-
dinates by usually 40-50 nm or more. The JTWC warnings are also the
source of the 1-minute average maximum sustained wind values included
in the tracks file. Additionally, information describing details of
satellite imagery and atmospheric circulation features included in
the narratives is often gleaned from the JTWC warnings.
A description of the Australian Cyclone Severity Scale can be found
on the Australian Bureau of Meteorology's official website:
http://www.bom.gov.au/info/cyclone/>
Click on the link 'Cyclone Severity Categories'
or on 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://australiasevereweather.com/cyclones/history.htm>
Northwest Australia/Southeast Indian Ocean
Tropical Activity for April
------------------------------------------
Tropical cyclone activity was non-existent in waters off Northwest
Australia and in the Southeast Indian Ocean after the demise of Severe
Tropical Cyclone Chris in early February through the end of March. A
tropical LOW formed during the first week of April south of Java and
had intensified into Tropical Cyclone Dianne very near Cocos Island by
the 7th. Dianne moved west-southwestward and had strengthened into a
severe tropical cyclone (hurricane) by the time it reached longitude 90E
and moved out of the Australian Region. Mauritius renamed the cyclone
Jery, and it became a fairly strong cyclone as it moved southward just
west of 90E.
A few days after the formation of Tropical Cyclone Dianne, another LOW
northwest of Darwin began developing and had intensified into a tropical
cyclone by the 10th. The cyclone, named Bonnie by the Darwin TCWC,
followed a westerly track at a rather low latitude and brushed the
Indonesian islands of Timor and Sumba. For several days forecasts
consistently called for Bonnie to strengthen, but the cyclone never
intensified above 50 kts and eventually weakened and dissipated southeast
of Cocos Island.
TROPICAL CYCLONE DIANNE-JERY
(TC-21S / MFR 13)
5 - 13 April
------------------------------------------------
A. Storm Origins
----------------
A persistent area of deep, unorganized convection developed on 4 April
approximately 190 nm northeast of Cocos Island. CIMSS upper-air products
showed the disturbance to be located in a region of weak to moderate
vertical shear with fair outflow aloft. A QuikScat pass around 1800 UTC
suggested that an associated weak LLCC was embedded in a near-equatorial
trough situated along latitude 12S. By 1800 UTC on 5 April the system
was located about 250 nm northeast of Cocos Island, and animated satel-
lite imagery depicted an increase in deep convection to the northeast of
the broad LLCC. A 05/1100 UTC QuikScat pass had indicated winds of 15 to
20 kts and a 200-mb analysis revealed improved outflow over the distur-
bance; therefore, JTWC upgraded the development potential to fair.
JTWC issued a TCFA at 1100 UTC on the 6th--deep convection was con-
tinuing to increase near the center and a convective band was developing
in the southern quadrant. A 200-mb analysis indicated that the system
was beneath the subtropical ridge axis in a region of light shear, and a
QuikScat pass revealed winds of 20-25 kts associated with the LOW. A
later QuikScat pass indicated winds had increased to 30 kts within the
band to the south of the center. JTWC issued their first warning on
TC-21S at 07/0000 UTC. The initial warning intensity (1-min avg) was
estimated 35 kts, based on CI estimates of 35 kts. There had been a
recent significant development of deep convection over the LLCC. The
system was centered only about 75 nm east-southeast of Cocos Island and
was moving west-southwestward at 6 kts. A mid-level ridge extending from
the west coast of Australia was expected to influence the track for the
next few days. At 0300 UTC the Perth TCWC issued a gale warning for the
LOW, indicating the likelihood of tropical cyclone development during
the next 12-18 hours. Just two hours later another warning upgraded
the system to Tropical Cyclone Dianne with maximum 10-min mean winds
estimated at 45 kts. Dianne's center was very near Cocos Island at the
time it was named as a tropical cyclone, moving west-southwestward at
14 kts.
B. Track and Intensity History
------------------------------
At 07/1200 UTC Tropical Cyclone Dianne was located about 90 nm south-
west of Cocos Island, moving west-southwestward at 11 kts. There had
been a significant increase in deep convection over the LLCC with a
recent TRMM pass revealing a developing low-level banding eye feature.
JTWC upped the 1-min avg MSW estimate to 55 kts, and Perth also upped the
intensity to 55 kts at 1600 UTC. Dianne continued moving in a west-
southwesterly direction, reaching a point about 260 nm southwest of Cocos
Island by 0000 UTC on 8 April. A 07/2300 UTC TRMM pass had revealed
tightly-curved bands with a developing banding eye feature. Based on
this and CI estimates of 55 and 65 kts, JTWC upped the 1-min avg MSW to
65 kts. Perth increased the 10-min avg MSW estimate to a comparable
60 kts at 0400 UTC.
At 08/1200 UTC Tropical Cyclone Dianne was located approximately
400 nm west-southwest of Cocos Island, still moving west-southwestward at
12 kts as it was steered by a mid-level ridge to the southeast. Earlier
visible imagery had revealed a cloud-filled banding eye while animated
water vapor imagery showed an improving single poleward outflow channel
that was being enhanced by the approach of a shortwave trough. Satellite
intensity estimates were 77 and 90 kts, so JTWC upped the 1-min avg MSW
to 80 kts. In their next warning, at 1600 UTC, Perth increased the
intensity to 75 kts, making Dianne a severe tropical cyclone (hurricane).
Dianne at this time was located about 465 nm west-southwest of Cocos
Island--just east of longitude 90E. By 1800 UTC the storm had crossed
into the Southwest Indian Ocean basin and had been renamed Jery by the
Mauritius Meteorological Service. The 1800 UTC warning from MFR,
however, did not concur with Perth's last assigned intensity--the MSW
was reported at only 60 kts. This was increased to 80 kts six hours
later, in good agreement with JTWC's estimated 1-min avg MSW of 90 kts.
Dianne-Jery by this time was located roughly 500 nm west-southwest of
Cocos Island and had turned to a south-southwesterly track at 9 kts.
Satellite imagery revealed that a 15-nm diameter eye had developed.
MFR continued to report the intensity at 80 kts through 0600 UTC but
lowered it to 75 kts at 09/1200 UTC. Interestingly, it was at 1200 UTC
that JTWC estimated their peak 1-min avg MSW of 105 kts, based on CI
estimates of 90 and 105 kts. Animated enhanced infrared imagery indi-
cated that the storm had had strong poleward outflow during the previous
12 hours which had helped to intensify it some. Based on JTWC's warnings
the gale radii were: 150 nm to the northeast and southeast, 120 nm to the
southwest, and 90 nm to the northwest. MFR's warnings indicated gales
extended outward 180 nm in the southern semicircle and less elsewhere.
The radius of storm-force winds was on the order of 40-45 nm. At 1800
UTC MFR brought the MSW down to 70 kts, and at 10/0000 UTC JTWC lowered
their 1-min avg MSW estimate to 95 kts. Dianne-Jery was then located
approximately 650 nm southwest of Cocos Island, moving southward at
7 kts, and was experiencing shearing in the southwest quadrant.
MFR and JTWC lowered their intensity estimates to 60 and 65 kts,
respectively, at 1200 UTC. There was no longer any deep convection in
the western semicircle and open-cell cumulus could be seen wrapping into
the center. The cirrus shield extended toward the southeast, and a
recent TRMM pass revealed a partially-exposed center--extratropical
transition was well underway. By 0000 UTC on the 11th Dianne-Jery was
located about 720 nm southwest of Cocos Island and had turned to the
southeast. MFR and JTWC had lowered their MSW estimates to 50 and
60 kts, respectively, based on CI estimates of 55 and 65 kts. A SSM/I
pass at 11/0000 UTC indicated a completely-exposed LLCC with deep con-
vection sheared to the southeast and a large band of dry air to the
north beginning to wrap into the center.
JTWC issued their final warning on Dianne-Jery at 11/1200 UTC, clas-
sifying it as extratropical. The system was located about 800 nm south-
west of Cocos Island and moving south-southeastward at 9 kts. The final
warning intensity from JTWC was 35 kts. MFR was reporting 40 kts, but
had also classified the system as extratropical. The remnant gale
re-entered Perth's AOR at 12/0000 UTC. The Perth TCWC issued gale warn-
ings on the system until 13/1200 UTC when it was located approximately
850 nm west of Perth.
C. Comparisons Between JTWC and Other Centers
---------------------------------------------
Intensity estimates between JTWC and Perth during Dianne's early life
were in close agreement, and after the storm had crossed 90E and become
Dianne-Jery, JTWC's 1-min avg MSW and MFR's 10-min avg MSW estimates
also agreed rather closely except at 09/1200 and 10/0000 UTC. As noted
above JTWC increased their MSW to 105 kts while MFR lowered the 10-min
avg MSW to 75 kts, equivalent to a 1-min avg MSW of 85 kts. Six hours
later JTWC had reduced their estimate to 95 kts and MFR had lowered
theirs to 70 kts, equivalent to an 80-kt 1-min avg MSW. However, by
1200 UTC the respective intensity estimates were back in very close
agreement.
D. Damage and Casualties
------------------------
No reports of damage or casualties resulting from Tropical Cyclone
Dianne-Jery have been received.
TROPICAL CYCLONE BONNIE
(TC-22S)
9 - 15 April
-------------------------------------------
A. Storm Origins
----------------
A STWO issued by JTWC at 1800 UTC on 7 April noted that an area of
unorganized convection had developed approximately 325 nm northeast of
Darwin in the Arafura Sea. CIMSS products indicated weak to moderate
vertical shear over the region with fair outflow aloft. Twenty-four
hours later the disturbance was centered about 270 nm north of Darwin.
Animated satellite imagery depicted unorganized and scattered convection
associated with a weak LLCC. A 200-mb analysis indicated divergence
aloft associated with an upper-level ridge extending along latitude 12S.
The Darwin TCWC gave the LOW a high potential for tropical cyclone devel-
opment within the next 72 hours. JTWC issued a TCFA at 1730 UTC on the
9th, noting the continuing increase in deep convection near the LLCC.
The system was located approximately 300 nm northwest of Darwin, and at
1800 UTC the Darwin TCWC issued a gale warning for the LOW in anticipa-
tion of its developing into a tropical cyclone within the next 12-24
hours. At 0000 UTC on 10 April, Darwin upgraded the system to Tropical
Cyclone Bonnie, located about 130 nm east of the island of Timor, moving
west-southwestward at 11 kts. At the same time JTWC issued their first
warning on Bonnie, but with an initial intensity of only 30 kts.
B. Track and Intensity History
------------------------------
By 1200 UTC on 10 April, Bonnie had entered Perth's AOR and was
located over south-central Timor, moving west-southwestward at 9 kts.
The island was inhibiting development somewhat with a 10/1320 UTC SSM/I
pass showing most of the deep convection confined to the southern semi-
circle. Bonnie was forecast to track west-southwestward under the
steering influence of a mid-level ridge extending from Australia into
the Timor Sea. The cyclone was situated beneath diffluent flow with good
outflow aloft. By 0000 UTC on the 11th Bonnie's center had moved out
over the Savu Sea. Both Perth and JTWC increased their respective inten-
sity estimates to 40 kts, based on CI estimates of 45 kts (1-min avg) and
a synoptic report of 35 kts from ship ZCA07. A 10/2214 UTC SSM/I pass
had revealed that deep convection was beginning to wrap into the center
from the north and east. The estimated MSW had increased to 45 kts by
11/1200 UTC (from both Perth and JTWC). Bonnie for the time being was
moving westward, a motion which carried it skimming over the southern
portion of the Indonesian island of Sumba. Convection once more
decreased as the cyclone interacted with a landmass.
By 12/0000 UTC the center of Tropical Cyclone Bonnie was once more
over water, moving west at 12 kts. JTWC increased their 1-min avg MSW
estimate to 50 kts at this time, and Perth also upped the intensity to
50 kts at 0400 UTC. The storm was located about 700 nm north of Onslow,
and recent TRMM and SSM/I imagery depicted a developing banding feature
extending over the southwest quadrant. A 12/1039 UTC SSM/I pass indi-
cated that the deep convection lacked organization and was sheared to
the west of the LLCC. JTWC dropped their intensity to 45 kts at 1200
UTC, but Perth's 10-min avg MSW estimate remained at 50 kts through
13/0100 UTC. Bonnie was located about 200 nm south of Java at 0000 UTC
on the 13th, moving west-southwestward at 15 kts. Perth decreased the
intensity to 45 kts at 0400 UTC, and at 1200 UTC JTWC dropped their 1-min
avg MSW estimate to 40 kts. Animated visible and infrared imagery showed
that development had been hindered by interaction with Java. Deep con-
vection had decreased earlier, although some had recently redeveloped,
and the center had become partially-exposed.
At 14/0000 UTC the cyclone was located some 300 nm south of Java,
still trekking west-southwestward. The intensity estimates from Perth
and JTWC were 45 and 40 kts, respectively. A SSM/I pass at 13/2315 UTC
revealed that an increase in the deep convection and organization of
the system had occurred over the past few hours. This apparent inten-
sification trend, however, was short-lived. By 1200 UTC most of the deep
convection had dissipated. JTWC lowered their intensity estimate to
35 kts, whereas Perth was still reporting the MSW at 45 kts. Bonnie at
this time was located approximately 200 nm south-southwest of Christmas
Island. Perth lowered the 10-min avg MSW to 40 kts at 1600 UTC, and at
2300 UTC issued their final gale warning on Bonnie.
JTWC issued two more warnings on the system. The 15/0000 UTC warning
placed Bonnie's center about 340 nm southeast of Cocos Island, moving
west-southwestward at 16 kts. The MSW (1-min avg) was estimated at
35 kts, based on CI estimates of 30 and 35 kts. Convection had increased
once again during the past six hours but remained disorganized. Bonnie
was forecast to weaken as it encountered increasing vertical shear. The
final JTWC warning at 1200 UTC placed the center about 250 nm south-
southeast of Cocos Island, moving west at 16 kts. The intensity was
dropped to 30 kts. Animated infrared imagery indicated that convection
had dissipated near the LLCC and only scattered deep convection remained
northwest of the center. Multi-spectral imagery depicted a rapidly
weakening LLCC.
C. Comparisons Between JTWC and Other Centers
---------------------------------------------
Intensity estimates from JTWC compared reasonably well with those from
the Darwin and Perth TCWCs after conversion to the same time averaging
period. In general JTWC's reported intensities ran a little lower than
those from the Australian warning centers.
D. Damage and Casualties
------------------------
Although the center of Tropical Cyclone Bonnie traversed two of the
islands of Indonesia, no damage or casualties are known to have resulted.
*************************************************************************
NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E
Activity for April: No tropical cyclones
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SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E
Activity for April: 2 tropical depressions
1 possible subtropical cyclone
Sources of Information
----------------------
The primary sources of tracking and intensity information for
South Pacific tropical cyclones are the warnings and advisories
issued by the Tropical Cyclone Warning Centres at Nadi, Fiji (for
waters north of latitude 25S), and Wellington, New Zealand (for
waters south of latitude 25S). References to sustained winds imply
a 10-minute averaging period unless otherwise stated.
In the companion tropical cyclone tracks file, I occasionally
annotate positions from warnings issued by the Joint Typhoon Warning
Center (JTWC) of the U. S. Air Force and Navy, located at Pearl
Harbor, Hawaii, when they differ from the Southern Hemisphere
centres' coordinates by usually 40-50 nm or more. The JTWC warnings
are also the source of the 1-minute average maximum sustained wind
values included in the tracks file. Additionally, information
describing details of satellite imagery and atmospheric circulation
features included in the narratives is often gleaned from the JTWC
warnings.
South Pacific Tropical Activity for April
-----------------------------------------
A fourth consecutive month passed without any tropical cyclones devel-
oping in the South Pacific east of longitude 160E. Fiji classified two
systems as tropical depressions--numbered 15F and 16F. Tropical Depres-
sion 15F was a weak, short-lived system on the first two days of the
month. At 0300 UTC on the 1st, the system was centered roughly 400 nm
northwest of Noumea, New Caledonia. The depression drifted generally
east-southeastward and was located about 250 nm northwest of Noumea when
it was last mentioned at 02/0600 UTC. Tropical Depression 16F was first
noted about 320 nm north-northeast of Port Vila, Vanuatu, on the 17th.
However, at 18/0600 UTC, the center was significantly relocated 275 nm
southward to a point about 100 nm east-northeast of Port Vila. Over the
next few days the depression meandered around in the same area, perhaps
drifting back to the north some, and was located north of Vanuatu when
it was last referenced at 0600 UTC on the 23rd. No gale warnings
were issued by Nadi in association with this depression, but Tropical
Disturbance Summaries issued by that office did note that fairly strong
winds were occurring on the southern flank of the system from the 18th
through the 21st due to the gradient with a strong HIGH centered near New
Zealand. By the 22nd the HIGH had moved eastward and the winds abated.
Another low-pressure system which caught the attention of quite a few
tropical weather observers formed in the Southeast Pacific near latitude
30S well east of the Dateline during the first few days of April. This
system was handled as a non-tropical gale in warnings issued by the
Wellington office, but did have some organized convection and some
characteristics of tropical and subtropical cyclones, even sporting an
eye-like feature at one point. Dr. Karl Hoarau of Cergy-Pontoise
University in France has agreed to study this system and if possible,
generate a track for it. When Karl has completed his analysis, I will
include the results as a Feature of the Month in a subsequent summary.
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EXTRA FEATURE
In order to shorten the amount of typing in preparing the narrative
material, I have been in the habit of freely using abbreviations and
acronyms. I have tried to define most of these with the first usage
in a given summary, but I may have missed one now and then. Most of
these are probably understood by a majority of readers but perhaps a
few aren't clear to some. To remedy this I developed a Glossary of
Abbreviations and Acronyms which I first included in the July, 1998
summary. I don't normally include the Glossary in most months in
order to help keep them from being too long. If anyone would like to
receive a copy of the Glossary, please e-mail me and I'll be happy
to send them a copy.
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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: apr02.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: apr02.sum, for
example.
Back issues can also be obtained from the following websites
(courtesy of Michael Bath, Michael V. Padua and Michael Pitt):
http://australiasevereweather.com/cyclones/>
http://www.typhoon2000.ph> OR http://66.40.4.61>
http://www.qisfl.net/home/hurricanemike>
Another website where much information about tropical cyclones may
be found is the website for the UK Meteorological Office. Their site
contains a lot of statistical information about tropical cyclones
globally on a monthly basis. The URL is:
http://www.met-office.gov.uk/sec2/sec2cyclone/sec2cyclone.html>
TROPICAL CYCLONE REPORTS AVAILABLE
JTWC now has available on its website the complete Annual Tropical
Cyclone Report (ATCR) for 2001 (2000-2001 season for the Southern
Hemisphere). ATCRs for earlier years are available also.
The URL is: http://199.10.200.33/jtwc.html>
Also, TPC/NHC has available on its webpage nice "technicolor"
tracking charts for the 2001 Atlantic and Eastern North Pacific
tropical cyclones; also, preliminary storm reports for all the 2001
Atlantic and Eastern North Pacific cyclones are now available, as
well as track charts and reports on storms from earlier years.
The URL is: http://www.nhc.noaa.gov>
A special thanks to Michael Bath of Wollongbar, New South Wales,
Australia, for assisting me with proofreading the summaries.
Prepared by: Gary Padgett
E-mail: [email protected]
Phone: 334-222-5327
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|
Document: summ0204.htm
Updated: 27th December 2006 |
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