[Index]
Monthly Global Tropical Cyclone Summary May 1999
[Summaries and Track Data] [Prepared by Gary Padgett]
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Monthly Global Tropical Cyclone Summary May 1999 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
MAY, 1999
(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.)
GLOBAL TROPICAL CYCLONE TERMINOLOGY REVIEW
The following is a synopsis of the terminology used by the various
TCWCs to describe the different stages of tropical cyclone development
and intensification. I have been waiting for a relatively quiet month
such as May has been to do this. This table gives the formal
terminology used to refer to a given cyclone in warnings and
advisories. For example, the Saffir/Simpson category is widely
utilized in the U. S. to describe a hurricane's intensity, but the
advisories do not refer to a hurricane formally as "Category Four
Hurricane Xerxes" in the title line of the advisories. Also, in the
U. S. the adjective "severe" may be frequently used to describe the
character of a hurricane, but is not formally used as the descriptor
for a given cyclone intensity range as it is in some basins.
1. ATLANTIC and NORTHEAST PACIFIC Basins - TPC/NHC (also CPHC)
MSW Averaging Period: 1 minute
Tropical Cyclone - generic term for systems of all intensities
Tropical Disturbance - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued/ usually corresponds to Dvorak
ratings less than T2.0
Tropical Depression - fairly well-defined low-level circulation/
MSW less than 34 kts/ Dvorak rating usually T2.0
Tropical Storm - MSW in range of 34-63 kts/ Dvorak rating of T2.5,
T3.0, or T3.5
Hurricane - MSW exceeding 63 kts/ Dvorak rating of T4.0 or higher
The point at which regular advisories are initiated is a little
subjective. A system with a Dvorak rating of T1.5 might be upgraded
to a tropical depression if it were in a position to affect a populated
area and/or if it seemed to be rapidly intensifying and its development
potential was considered excellent.
2. JTWC for NORTHWEST PACIFIC Basin Only
MSW Averaging Period: 1 minute
Tropical Cyclone - generic term for systems of all intensities
Tropical Disturbance - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued/ usually corresponds to Dvorak
ratings of T1.0 or less/ MSW generally less than 25 kts
Tropical Depression - fairly well-defined low-level circulation/
MSW 25-34 kts/ Dvorak rating usually T1.5 - T2.0
Tropical Storm - MSW in range of 34-63 kts/ Dvorak rating of T2.5,
T3.0, or T3.5
Typhoon - MSW exceeding 63 kts/ Dvorak rating of T4.0 or higher
Supertyphoon - MSW reaching or exceeding 130 kts
Although not previously the case, in recent years JTWC has begun
issuing regular warnings on tropical depressions when the MSW reaches
25 kts. In earlier years the warning criterion was the
subjective analysis that the system would likely produce tropical
storm force winds within 48 hours. I have been told that the term
"supertyphoon" was possibly going to be dropped from official use,
but it was still being used during the 1998 season.
3. JTWC for NORTH INDIAN OCEAN and SOUTHERN HEMISPHERE
MSW Averaging Period: 1 minute
For the North Indian Ocean and all Southern Hemisphere regions, JTWC
(NPMOC for the South Pacific east of longitude 180) uses only the
generic term "Tropical Cyclone" to refer to systems of all intensities
in warning status. Warnings are usually initiated when the system
is forecast to produce gale/tropical storm force winds within 48 hours.
In many cases winds are already approaching this threshold when the
first warning is issued, and frequently the initial MSW is set at
35 kts.
4. NORTHWEST PACIFIC Basin - JMA (Japan)
MSW Averaging Period: 10 minutes
Tropical Cyclone - generic term for systems of all intensities
Low-pressure Area - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued
Tropical Depression - fairly well-defined low-level circulation/
MSW less than 34 kts
Tropical Storm - MSW in range of 34-47 kts/ Dvorak rating of T2.5
or T3.0
Severe Tropical Storm - MSW in range of 48-63 kts/ Dvorak rating
of T3.5 or T4.0
Typhoon - MSW exceeding 63 kts/ Dvorak rating of T4.5 or higher
The Japanese Meteorological Agency (JMA) is the World Meteorological
Organization's (WMO) official Regional Specialised Meteorological
Centre (RSMC) for the Northwest Pacific Basin. While adherring to
a 10-min averaging period for MSW, JMA normally equates 34 kts to a
Dvorak rating of T2.5; thus, JMA and JTWC agree in principle on the
threshold of tropical storm intensity. However, for very intense
typhoons, JMA's MSW estimates are usually far below those assigned
by JTWC. Other Asian nations' weather services issue tropical
cyclone warnings for portions of the Northwest Pacific region,
including the Philippines, Hong Kong, China, Vietnam, Taiwan, and
Korea. Warnings from these weather services are issued independently
of JMA but utilize the same terminology and are usually reasonably
close to JMA's positions and intensity estimates.
5. NORTH INDIAN OCEAN Basin - IMD (India)
MSW Averaging Period: 1 minute
Low-pressure Area - weak, diffuse area of low pressure without
a definite surface circulation
Depression - well-defined low-level circulation but with MSW
generally less than 28 kts/ Dvorak rating of T1.5
Deep Depression - depression with MSW in range of 28-33 kts/
Dvorak rating of T2.0
Cyclonic Storm - tropical cyclone with MSW in range of 34-47 kts/
Dvorak rating of T2.5 - T3.0
Severe Cyclonic Storm - tropical cyclone with MSW in range of
48 - 63 kts/ Dvorak rating of T3.5
Very Severe Cyclonic Storm - tropical cyclone with MSW exceeding
63 kts / Dvorak rating of T4.0 or higher
The Indian Meteorological Department (IMD) is the WMO's RSMC for
the North Indian Ocean (Bay of Bengal and Arabian Sea), although the
meteorological services of other nations may issue warnings for
portions of the basin.
6. SOUTH INDIAN OCEAN Basin (West of 90E)
MSW Averaging Period: 10 minutes
Tropical Disturbance - term is used for all tropical weather
disturbances from weak ill-defined systems to fairly well-
defined systems with MSW up to 27 kts (Beaufort Force 6 -
Dvorak T2.0) which would be classified as tropical depressions
by many TCWCs. Regular bulletins are issued for the stronger
tropical disturbances.
Tropical Depression - MSW in range of 28-33 kts (Beaufort Force 7 -
Dvorak rating of T2.5)
Moderate Tropical Storm - MSW in range of 34-47 kts/ Dvorak rating
of T3.0 - T3.5
Severe Tropical Storm - MSW in range of 48-63 kts/ Dvorak rating
of T4.0 - T4.5
Tropical Cyclone - MSW in range of 64-89 kts/ Dvorak rating of
T5.0 - T5.5
Intense Tropical Cyclone - MSW in range of 90-115 kts/ Dvorak
rating of T6.0 - T7.0
Very Intense Tropical Cyclone - MSW exceeding 115 kts/ Dvorak
rating of T7.5 - T8.0
The WMO's RSMC for the South Indian region is the TCWC on the French
island of La Reunion; however, names are actually assigned by the
sub-regional centres on Mauritius (east of 55E) and Madagascar (west of
55E). The La Reunion TCWC employs a conversion factor of 0.80 to
convert the 1-minute MSW Dvorak scale to an equivalent 10-minute
average scale.
7. AUSTRALIAN REGION (longitude 90E eastward to longitude 160E)
MSW Averaging Period: 10 minutes
Tropical LOW - term is used to describe disturbances ranging from
diffuse, ill-defined low-pressure areas all the way to well-
organized tropical depressions with MSW up to 33 kts
Tropical Cyclone - MSW in range of 34-63 kts/ Dvorak rating ranging
from a strong T2.5/weak T3.0 to T4.0
Severe Tropical Cyclone - MSW exceeding 63 kts/ Dvorak rating of
T4.5 or higher
Warnings in the Australian Region are issued by three separate
TCWCs: Brisbane (Queensland), Perth (Western Australia), and Darwin
(Northern Territory). In addition to these, a TCWC at Port Moresby,
Papua New Guinea (formerly an Australian territory) issues warnings
for a small portion of the region near and east of the island of New
Guinea. The Papua New Guinea region has an extremely low incidence
of tropical cyclone occurrences. The Australian centres avoid use of
the term "tropical depression" in public advices primarily to reduce
possible confusion with the use of the term "depression" in
association with extratropical systems; and also possibly because until
recently (early 1990's), in the South Indian Ocean Basin, a "tropical
depression" meant any system with winds up to 63 kts (hurricane force).
The Australian TCWCs utilize a conversion factor of 0.88 or 0.90 to
modify the 1-minute Dvorak scale to an equivalent 10-minute average
scale.
8. SOUTHWEST PACIFIC Basin (east of longitude 160E)
MSW Averaging Period: 10 minutes
Tropical Disturbance - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued/ usually corresponds to Dvorak
ratings less than T2.0
Tropical Depression - fairly well-defined low-level circulation/
MSW less than 34 kts/ Dvorak rating usually T2.0 or weak T2.5
Tropical Cyclone - MSW exceeding 33 kts and more or less occurring
in all quadrants/ Dvorak rating of strong T2.5/T3.0 or higher
The TCWC at Nadi, Fiji, is the RSMC for the Southwest Pacific basin
but the meteorological service of New Zealand (Wellington) issues
warnings for systems that move (or very rarely form) south of latitude
25S. The official definition of a tropical cyclone in WMO Region 5
(Australia and the South Pacific) requires that gales more or less
surround the center. From my observations over the past two years,
it seems that this is more of a factor in the Southwest Pacific than
in the Australian Region. In the Fiji AOR tropical depressions
routinely have the MSW given as 35-40 kts but in one or two quadrants
only. The Fiji TCWC employs a 1-minute to 10-minute MSW conversion
of 0.90 when adjusting the Dvorak scale.
***********************************************************************
MAY HIGHLIGHTS
--> Deadly and destructive Arabian Sea cyclone strikes Pakistan
and northwestern India
***********************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for May: No tropical cyclones
Atlantic Activity for May
-------------------------
No tropical cyclones were observed in the Atlantic basin during
May, which is usually the case. What is unusual is that it has been
18 years since the last named May tropical storm in the Atlantic--that
was Tropical Storm Arlene in early May, 1981. Since the advent of
aerial reconnaissance of tropical cyclones in 1944, the longest prior
period between May tropical storms had been 11 years. However, there
was an area of disturbed weather in the southwestern Caribbean Sea from
around 16 - 24 May which several numerical models forecast would
develop into some type of storm, whether tropical or subtropical.
Convection increased from the 16th through the 20th over a wide area,
and the consistency of the models was such that TPC/NHC issued a
Special Tropical Disturbance Statement at 20/1930 UTC. A surface
trough was present east of Nicaragua by 20/1800 UTC, and an approaching
tropical wave spawned a surface LOW by 1200 UTC on 21 May. This was
accompanied by a dramatic increase in deep convection. Shear remained
high, however, and deep convection had collapsed and contracted by
late on the 22nd, and the surface LOW had dissipated by the afternoon
of the 23rd.
(John Wallace of San Antonio, TX, sent me a very detailed synopsis
of this disturbance, and the information included above is taken from
John's summary. A special thanks to John for sending this to me.)
***********************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for May: No tropical cyclones
***********************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for May: 1 typhoon
NOTE: Most of the information on each cyclone's history presented in
the narrative will be based upon JTWC's advisories, and references to
winds should be understood as a 1-min avg MSW unless otherwise noted.
However, in the accompanying tracking document I have made comparisons
of coordinates with JMA (Japan) and the Philippines (PAGASA) when their
positions differed from JTWC's by usually 40-50 nm or more. Also, as
announced earlier in a separate posting, a column of 10-min avg MSW
is included--the values being obtained from either PAGASA's or JMA's
advisories. A special thanks to Michael V. Padua, owner of the Typhoon
'99 webpage, for sending me the PAGASA tracks.
In the title line for each storm I plan to reference all the cyclone
names/numbers I have available: JTWC's depression number and name (if
any), JMA's tropical storm numeric designator, and PAGASA's name for
systems forming in or passing through their area of responsibility.
Typhoon Leo (TC-05W / TY 9902)
27 April - 2 May
-------------------------------
Typhoon Leo formed in late April in the South China Sea and moved
generally on a slow northeasterly course toward southern China. Leo
became a rather intense typhoon with MSW estimated at 110 kts.
However, as Leo approached the southern Chinese coast near Hong Kong,
it collapsed very rapidly due to strong westerly vertical shear.
The complete history of Typhoon Leo was covered in the April Tropical
Cyclone Summary.
ADDENDUM to April Summary
-------------------------
I was unable to access JMA bulletins for Tropical Storm Jacob/Karing
during early April; hence, there were no central pressure estimates
given in the track for this system. Steve Young of Long Beach, CA,
has sent me the JMA pressures for Jacob/Karing:
DATE TIME PRESS DATE TIME PRESS
(UTC) (MB) (UTC) (MB)
------------------------ ------------------------
99 APR 06 0600 1006 99 APR 08 0600 1004
99 APR 06 1200 ---- 99 APR 08 1200 1004
99 APR 06 1800 1006 99 APR 08 1800 1008
99 APR 07 0000 1006 99 APR 09 0000 1008
99 APR 07 0600 1006 99 APR 09 0600 1006
99 APR 07 1200 1008 99 APR 09 1200 ----
99 APR 07 1800 1008 99 APR 09 1800 1006
99 APR 08 0000 1008 99 APR 10 0000 ----
(Thanks to Steve for passing this information along.)
NOMINAL CENTRAL PRESSURE-MAXIMUM SUSTAINED WIND
RELATIONSHIP USED BY JTWC FOR THE
NORTHWEST PACIFIC BASIN
-----------------------------------------------
JTWC does not include estimates of central pressure (CP) in their
tropical cyclone warnings, but they do make use of an empirically
derived CP/MSW relationship in operational analysis and also in their
post-season reports and summaries. A table of this relationship was
published in 1977, and John Wallace has sent this to me with a few
minor changes he incorporated based upon the final estimates reported
in JTWC's Annual Tropical Cyclone Reports. I am including the table
here as John sent it to me. It should be understood that these CP/MSW
relationships represent typical situations based on average-sized
storms in environments of average ambient pressures. A midget-sized
storm near a region of higher-than-normal environmental pressures can
have a MSW considerably higher than the nominal values, while on the
other hand the MSW in a very large storm in a region of lower-than-
normal pressures can be somewhat lower than the table implies. (A
special thanks to John for sending this information to me.)
MSW(kts) CP(mb) MSW(kts) CP(mb) MSW(kts) CP(mb)
----------------- ----------------- -----------------
25 1002 75 968 125 916
30 1000 80 963 130 910
35 997 85 958 135 904
40 994 90 954 140 898
45 991 95 949 145 892
50 987 100 944 150 885
55 984 105 938 155 878
60 980 110 933 160 872
65 976 115 927 165 865**
70 972 120 922
** - Not observed to date. The lowest measured pressure was 870 mb
in Typhoon Tip in October, 1979.
***********************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for May: 1 tropical cyclone of hurricane intensity
NOTE: The tracking and intensity information for North Indian Ocean
Basin tropical cyclones is based primarily upon operational warnings
from the Joint Typhoon Warning Center of the U. S. Air Force and Navy
(JTWC) at Pearl Harbor, Hawaii. Occasionally some information may
be gleaned from the daily Tropical Weather Outlooks and other bulletins
issued by the Indian Meteorological Department, which is the WMO's
RSMC for the basin.
The MSW are based on a 1-min averaging period, which is used by
all U. S. civilian and military weather services for tropical cyclone
warnings. For synoptic observations in the North Indian region,
both 10-min and 3-min average winds are employed, but IMD makes no
attempt to modify the Dvorak scale for estimating tropical cyclone
intensity; hence, a 1-min avg MSW is implied. In the North Indian
basin JTWC usually does not initiate warnings until a system is
well-organized and likely to attain tropical storm status within
48 hours.
North Indian Ocean Activity for May
-----------------------------------
In 1998 the only basin to see any tropical cyclone development
during the month of May was the North Indian Ocean. This was the
case in 1999 also, except for a rather unusual, possibly hybrid,
system in the South Pacific Ocean. Another similarity to 1998,
and an unfortunate one, was the landfall of an intense cyclone in
the same general coastal region of northwestern India. A cyclone
in June, 1998, struck the Gulf of Cutch region in Gujurat state
with the loss of well over 1000 lives. This year's storm made
landfall a little farther north with southeastern Pakistan being
the hardest hit region.
Tropical Cyclone (TC-02A)
16 - 22 May
--------------------------
An area of disturbed weather hung around off and near the south-
eastern coast of India for several days during early May. The system
underwent diurnal oscillations for a few days as convection would fire
up in the early morning, exhibit some cyclonic rotation during the
day, and then dissipate at dusk. Finally, by early on 16 May,
convection had become organized well enough that JTWC issued a
Formation Alert at 0100 UTC. At 0600 UTC the first warning was issued
placing the center about 425 nm south of Bombay, or west of the city
of Mangalore. The depression was estimated to have a MSW of 30 kts.
The low-level center was embedded in a trough which extended north-
eastward over southern India. Six hours later the center was
relocated to the northwest based on information received from a pass
by the Tropical Rainfall Measurement Mission (TRMM) satellite.
The system initially moved northwestward, still connected to the
parent trough and guided by a mid-level ridge to its north.
Intensification proceeded at a fairly quick pace, with the storm
reaching hurricane force by 17/0600 UTC at a location approximately
300 nm south-southwest of Bombay. An anticyclone had developed
right over the cyclone and it continued to intensify. By 18/1200 UTC,
when the storm was passing about 325 nm west of Bombay, the MSW had
reached 100 kts. Initially the cyclone had been forecast to track
to the northwest and then more west-northwestward as the mid-level
ridge was forecast to build westward north of the storm. By this
scenario the storm would intensify up to a point, then began to
weaken as very dry air from the Arabian desert was entrained into
the circulation.
However, the ridge did not strengthen to the north but remained
east of the storm, and the still-intensifying cyclone turned to a
due northward course off the west coast of India, much like its
predecessor of a year earlier (TC-03A of 1998). A microwave imager
pass at 18/0436 UTC revealed the existence of concentric eyewalls
with radii of 9 nm and 44 nm. Peak MSW of 110 kts was reached by
0000 UTC on 19 May and was more or less maintained until landfall
around 20/0600 UTC. Shortly before landfall a warning from JTWC
noted that the system had an excellent convective structure and good
upper-level outflow in all quadrants. TC-02A made landfall around
0600 UTC on the 20th between Kajhar Creek and Kori Creek in western
Gujurat, India, not far from the Pakistani border. This point was
roughly 100 nm south-southeast of Karachi, Pakistan. The cyclone
was sporting a 25-30 nm diameter eye when it reached the coast.
The JTWC warning issued at 19/0300 UTC carried the following
statement: "This system is expected to weaken only slightly prior
to landfall, after which it will quickly weaken." However, the
cyclone was in no hurry to weaken after moving inland. Twelve
hours after making landfall JTWC was still estimating the MSW at
100 kts, and still at hurricane force when the final warning was
issued 24 hours after landfall! The reasons for this very slow
weakening after lanfall are not altogether clear, but three factors
may have contributed: the storm was over flat terrain (the Indus
River delta), there was no vertical shear, and the system was still
entraining very moist inflow from the Arabian Sea.
At the time the final JTWC warning was issued (21/0900 UTC), the
center was well inland and moving northeastward into more rugged
terrain. That warning placed the center about 275 km east of
Karachi. Based on some TRMM microwave imagery, the MSW were still
given as 65 kts but it was noted that almost all the convection had
diminished except for one outer cloud band located about 100 nm south
of the low-level center.
This cyclone made landfall a short distance farther north up the
coast from where the deadly June, 1998, cyclone struck. Pakistan
seems to have borne the brunt this time. Nonetheless, some strong
winds were felt in India. Dwarka, in Gujurat state, reported winds
to 82 kts, but it is not known whether or not these were gusts or
sustained winds. More than 50,000 persons were evacuated from the
area in advance of the cyclone. The Institute of Meteorology and
Geophysics in Karachi reported that some location in Pakistan
experienced a wind gust to 147 kts. This cyclone was likely the
strongest Arabian Sea cyclone to occur since the Dvorak method of
satellite imagery analysis was developed.
The latest information obtained by the author indicated that in
the Sindh province of Pakistan, at least 300 deaths were confirmed
with estimates reaching over 400. However, the report stated that
perhaps 9,000 persons were still missing. The fishing fleet was
heavily damaged and almost wiped out. Most standing crops were
destroyed and stores of grain and other foods were lost also.
About 60,000 hectares of farmland were seriously damaged, and more
than 10,000 head of cattle were killed. Estimates placed the number
of homes destroyed at more than 63,000 with another 44,000 damaged.
Most homes in the region are built of mud and many were washed away
by the huge waves.
For those who are interested in more details of this disaster,
several reports can be found at the following website:
http://wwwnotes.reliefweb.int>
Click on the "Natural Disasters" link located in the column at the
left.
***********************************************************************
SOUTH INDIAN OCEAN (SIO) - South Indian Ocean West of Longitude 90E
Activity for May: No tropical cyclones
***********************************************************************
AUSTRALIAN REGION (AUG) - From Longitude 90E Eastward to Longitude 160E
Activity for May: No tropical cyclones
Australian Region Activity for May
----------------------------------
No tropical cyclones occurred in the Australian Region during May.
A tropical depression (TD-26F) which formed in the Fiji AOR tracked
southward near and just east of the 160th meridian and had some effects
on the Australian coast. This system intensified and possibly
reached hurricane force, but its character was such that it was not
classified as a tropical cyclone. More information on this unusual
system can be found in the section of the summary covering the
Southwest Pacific basin.
CORRECTION to April Summary
---------------------------
Matthew Saxby pointed out an error I made in the April Tropical
Cyclone Summary in the discussion of the hybrid LOWs that affected
the Queensland coast in early February. I referred to Toowoomba
(Queensland) as an "island" centre, whereas Matthew's e-mail clearly
said "inland" centre (as opposed to a coastal station, as were all
the other sites referenced). Toowoomba (pop. 90,000 according to
Matthew) is situated along an escarpment a little over 100 km west
of Brisbane. Thanks to Matthew for pointing this out to me, and
my apologies for the mistake.
***********************************************************************
SOUTHWEST PACIFIC (SWP) - South Pacific Ocean East of Longitude 160E
Activity for May: 1 tropical depression/hybrid cyclone
Southwest Pacific Activity for May
----------------------------------
No tropical cyclones developed in the Southwest Pacific during the
month of May, but a tropical depression formed which became fairly
intense, likely as some sort of hybrid system. Exactly what to call
this storm is open to debate with differing opinions among tropical
meteorologists.
Tropical Depression (TD-26F)
20 - 26 May
-----------------------------
A disturbed area formed well off the Queensland coast during the
third week of May. Early on 20 May some numerical models were
forecasting the development of a fairly deep cyclonic storm. By
1800 UTC Nadi issued a warning on a new depression, placing the center
about 225 nm northwest of the northern tip of New Caledonia. At this
time the deepest convection lay just southeast of the low-level cloud
center, and the system was located just ahead of an approaching trough
with 50-kt northwesterly winds aloft. The system moved on a fairly
straight southerly track for the next five days, passing about
300 nm west of Noumea, New Caledonia, around 22/0600 UTC.
Fiji, in their warnings, were mentioning gales to 40 kts in the
southern quadrants at this time. An advisory issued at 21/1200 UTC
described the system as a "classical intense system developing with
an active monsoon trough and is located within a warm thickness ridge."
The low-level center was difficult to track at first since it was
obscured by mostly mid-level clouds, but around 21/1800 UTC it became
much better defined after it appeared to interact with an eastward
progressing 500-mb cut-off LOW. Feeder bands characteristic of a
tropical cyclone were not present, but the depression appeared to
be experiencing a high influx of moisture at mid-levels from the
northeast. Convection appeared to be supported by the divergence
present on the equatorward side of the subtropical jet. The reported
drop in central pressure from 1200 UTC to 1800 UTC (998 to 993 mb)
was supported by a report from ship ELIS8 located about 150 nm south
of the center.
The system continued slowly southward until the 25th, when it
accelerated rapidly south-southeastward, passing west of the southern
tip of New Zealand's South Island and near Auckland Island around
0600 UTC on 26 May. The Fiji advisory for 22/0600 UTC mentioned
that the low-level center was exposed on the northwest edge of
the convection (which was only around -40 C). However, the center
would at times seem to catch up with the convection. According to
Mark Lander of the University of Guam, early on 25 May the storm
had intensified, had central convection and extensive peripheral
banding, and looked more like a hurricane than at any previous time.
What is rather surprising is that JTWC issued no warnings at all on
this storm, which must indicate that it was not considered a tropical
cyclone by the forecasters and analysts there. Mark seems to be
the primary proponent of calling this system a tropical cyclone.
Jack Beven of TPC/NHC feels the system was in several regards
similar to the Atlantic hybrid system off the U. S. East Coast in
December, 1994, but that system was about 20-25 mb deeper and had
better convective organization near peak intensity. On 23 May the
storm exhibited an eye-like feature, but Jack indicated he would
hesitate to call it a true eye. Steve Ready applied a satellite
analysis procedure (developed by Mark Lander and Jeff Millar for
extratropical cyclones recently evolved from classical tropical
cyclones) to the system, and, after incorporating translational speed
effects, obtained a maximum 10-min MSW of 70 kts at 25/2300 UTC.
Jeff Callaghan of the Brisbane TCWC reports that the storm had
a signifcant impact on the Australian coast between 25S and 32S
although its closest approach was about 400 nm off the coast. There
were two helicopter rescues to stricken yachts just off Brisbane and
two more near Port Macquarie. Swells with wave heights to 9 m were
reported. Numerous ships reported winds well above gale force, and
there were a couple reporting winds in excess of 50 kts:
ELMQ 23/0600Z 150/50 kts near 26.3 S, 159.6 E
---- 23/1200Z 140/54 kts near 26.3 S, 154.0 E
The storm passed about 50 nm east of Lord Howe Island around
1200 UTC on 24 May. That station reported peak winds of 230/41 kts
with a gust to 57 kts at 24/1355 UTC. Steve Ready reported that
Secretary Island (located in the southwest of South Island) experienced
gusts to 78 kts as the storm brushed by New Zealand. Invercargill
(almost on the south coast) reported 60-kt winds at 2100 m and 84 kts
at 3050 m. Finally, as the (by now extratropical) system moved
rapidly south-southeastward on 26 May, it passed over a drifting
buoy near 52.5 S, 169.0 E which reported a minimum pressure of 975.2 mb
at 1249 UTC.
(A special thanks to Mark Lander, Steve Ready, Jeff Callaghan, and
Jack Beven for the information and discussion on this system. Also a
special thanks to Matthew Saxby for sending me warnings from Brisbane
and Sydney from which I compiled a track for this system after it
left the Fiji AOR.)
***********************************************************************
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
March as an example: may99.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: may99.sum, for
example.
Back issues can also be obtained from the following websites
(courtesy of Michael Bath, Michael V. Padua, Tom Berg, and Michael
Pitt):
http://australiansevereweather.com/cyclones/>
http://www.geocities.com/capecanaveral/6825>
http://www.hcane.com/tropcl.html>
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
I have discovered that JTWC now has available on its new website
the complete Annual Tropical Cyclone Report for 1997 (1996-1997 season
for the Southern Hemisphere). Also, tracks only for the 1998 tropical
cyclones are currently available.
The URL is: http://199.10.200.33/jtwc.html>
Also, TPC/NHC has available on its webpage nice "technicolor"
tracking charts for the 1998 Atlantic and Eastern North Pacific
tropical cyclones; also, preliminary storm reports for all the 1998
Atlantic cyclones are now available.
The URL is: http://www.nhc.noaa.gov/1998.html>
Prepared by: Gary Padgett
E-mail: [email protected]
Phone: 334-222-5327 (nights & weekends) / 850-882-2594 (weekdays)
***********************************************************************
***********************************************************************
|
Document: summ9905.htm
Updated: 18th March 2008 |
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