[Index]
Monthly Global Tropical Cyclone Summary March 1999
[Summaries and Track Data] [Prepared by Gary Padgett]
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Monthly Global Tropical Cyclone Summary March 1999 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
MARCH, 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.)
CHANGE IN COVERAGE OF WEAKER TROPICAL SYSTEMS
In order to save some preparation time for the summaries and perhaps
help me to get them completed a bit sooner, I have decided to decrease
the amount of narrative coverage for tropical depressions which fail
to reach tropical storm (tropical cyclone in Australia and Fiji AORs)
intensity. I will continue to include tropical depression tracks in
the companion tracking document I prepare since most TCWCs do not
archive tracks for weaker tropical systems in their official historical
databases (Best Tracks files). Generating the tracks for these systems
usually does not take too long, since they are normally short-lived,
and also, for many basins, the track-generation process is
semi-automated.
But writing the narrative takes more time, and once written, has to
be carefully proofread at least a couple of times. I will briefly
mention tropical depressions in an introductory paragraph for each
basin; and for those which cause significant effects such as flooding,
I will report on the damage and/or casualties for which the depression
was responsible.
The systems which will warrant "the full treatment" will be those
for which, as best I can determine, reached a 1-min avg MSW of
34 kts (Dvorak T2.5) since this is the most liberal criterion utilized
by any TCWC. Based upon the most common 1-min avg to 10-min avg
conversion factor in use, the difference between the two at the
threshhold of gale force amounts to only about 3 or 4 kts; and JMA,
while using the 10-min MSW for their warnings, equates Dvorak T2.5
to 35 kts and uses this as the threshhold for tropical storm intensity,
as do TPC/NHC, CPHC, and JTWC. India also does not modify the 1-min
Dvorak scale for assigning tropical cyclone intensities; hence, a
T-number of 2.5 essentially constitutes a Northern Hemisphere
standard for tropical storm intensity in the absence of any direct
wind observations.
Therefore, in order to maintain a consistent criterion for the
systems I include in the summaries, I will use a Dvorak rating of
T2.5 and/or a 1-min avg MSW (which normally would be assigned by
JTWC) as the criterion for the Southern Hemisphere also. However,
I will continue as always to use the terminology appropriate for each
basin, and when an unnamed Southern Hemisphere system is included, I
will make it clear that the given system was not considered a tropical
storm/tropical cyclone by the official TCWC for the basin in question.
***********************************************************************
MARCH HIGHLIGHTS
--> Mauritius and La Reunion affected by South Indian cyclone
--> Northwestern Australian coast struck by intense cyclone
***********************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for March: No tropical cyclones
***********************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for March: No tropical cyclones
***********************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for March: No tropical cyclones
***********************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for March: No tropical cyclones
***********************************************************************
SOUTH INDIAN OCEAN (SIO) - South Indian Ocean West of Longitude 90E
Activity for March: 1 tropical disturbance
1 tropical depression
1 tropical cyclone
The primary sources of information upon which the narrative is based
are the warnings issued by the TCWC on La Reunion Island, associated
with Meteo France, and which is the RSMC for the South Indian Ocean
basin. However, cyclones in this region are named by the sub-regional
centres on Mauritius and Madagascar with longitude 55E as the dividing
line between their respective areas. La Reunion only advises these
centres regarding the intensity of tropical systems. References to
sustained winds should be understood as implying a 10-min averaging
period unless otherwise stated. In the accompanying track file
some position comparisons have been made with JTWC's positions, and
warnings from JTWC were used as a source of 1-min avg MSW estimates.
(A special thanks to Philippe Caroff of the La Reunion TCWC for
sending me an analyzed Best Track File for Davina and TD E39899.
This forms the basis for the tracking information given for those
systems in the accompanying track file.)
South Indian Ocean Activity for March
-------------------------------------
March featured the most significant tropical system so far this
season in the South Indian Ocean west of 90E, and the first to reach
tropical cyclone (hurricane) intensity in this basin. Tropical
Cyclone Davina travelled on a long trajectory from near 90E to a
position just east of the southern Madagascar coast. The cyclone struck
Mauritius with hurricane force winds, causing considerable damage,
and later brushed by La Reunion as a severe tropical storm. Two
much weaker systems roamed the central South Indian also. Tropical
Disturbance E29899 (numbered as TC-26S by JTWC) entered the region
from the Perth AOR but was already weakening as it crossed 90E. Even
though weak, this disturbance was exceptionally long-lived, having
begun south of Java on 28 Feb and continuing as an identifiable system
until 27 Mar. This weak LOW meandered generally west-northwestward
to a position several hundred miles north of Mauritius by 16 Mar,
thence back eastward to a position roughly 200 nm southwest of Diego
Garcia where it dissipated by the 28th. Central MSW never
exceeded 25 kts although some peripheral winds to 30 kts were reported
in the southern semicircle. The other weaker system was classified
as a tropical depression (E39899) by La Reunion and as a very minimal
tropical storm (TC-29S) by JTWC. A brief description of this
system follows the discussion of Tropical Cyclone Davina.
Tropical Cyclone Davina (TC-25S)
1 - 19 March
---------------------------------
A tropical disturbance was observed in the monsoon trough on 1 Mar
at 0600 UTC located about 525 nm west of Cocos Island, or about 1000 nm
east-southeast of Diego Garcia. Under favorable upper-level outflow
and low vertical shear, the system slowly strengthened. The LOW
initially jogged eastward to a position just east of 90E, then began
to move on a fairly straight west-southwesterly course under the
influence of the subtropical ridge to its south. JTWC classifed the
system as a minimal tropical storm at 02/1800 UTC, but it was not
named by Mauritius until 4 Mar. Davina reached cyclone (hurricane)
intensity on 5 Mar and reached its peak intensity of 90 kts (105 kts
1-min MSW from JTWC) on 7 Mar. JTWC at one point was forecasting
Davina to possibly reach 130 kts, but the cyclone began to encounter
some mild vertical shearing on its eastern side which hampered any
further intensification.
Tropical Cyclone Davina sailed along at 15 kts or more on a
remarkably smooth trajectory which eventually took it very near the
islands of Mauritius and La Reunion. Davina was still at cyclone
intensity when it brushed the southeastern tip of Mauritius but had
begun to weaken by the time it grazed La Reunion. After passing
by the islands the storm slowed its forward motion dramatically and
drifted slowly and erratically generally northward and westward for
several days as it weakened into a tropical disturbance. A residual
LOW remained in the area east of southern Madagascar through 19 Mar.
Davina passed about 75 nm northwest of Rodrigues Island around
1800 UTC on 8 Mar. Information gleaned from Mauritian daily
newspapers and sent to me by Arvind Mungur indicated that the highest
gusts recorded on Rodrigues were 65 kts, but information provided
by Philippe Caroff states that the peak gust on Rodrigues was 75 kts.
Very little rain fell on the island (42 mm in 24 hrs)--not enough to
improve the current drought situation.
A still-potent Davina passed over the southeastern tip of Mauritius
around 2100 UTC on 9 Mar. Hurricane-force gusts were recorded for
seven hours, reaching a peak of 94 kts near the capital, Port Louis.
A peak gust of 92 kts was recorded at the Plaisance airport (about
14 nm from the storm's center). Gusts exceeding 87 kts were reported
at several locations in the eastern and southern regions. The
minimum pressure recorded at Plaisance airport was 974.9 mb. Rainfall
was relatively light as compared with most cyclones that have struck
the island. A maximum 24-hr measurement of 210 mm was recorded at
Medine in the center of Mauritius, and the average rainfall for the
island was only 90 mm. In spite of the rain, the drought situation
is alarming with the dry season approaching and storage reservoirs
at less than 50% of their capacity. Crops were hard hit with
destruction levels ranging from 30-100% for most crops.
Davina weakened and slowed between Mauritius and La Reunion and
was of severe tropical storm intensity when the center passed about
16 nm southeast of La Reunion. Winds were generally in the 55-65 kt
range, but gusts reached 92 kts at a spot on the northeastern coast
of the island very exposed to southerly winds. Rainfall amounts were
not overly impressive for La Reunion--ranging from 187 mm at Cilaos
to 394 mm on the volcano La Fournaise at an elevation of 2250 m.
However, the remnants of Davina remained to the southwest of the island
for several days, tracking erratically after encountering strong
vertical shear. This resulted in a very humid northerly flow over the
island, and heavy rains fell over the northern portion for about five
days. Significant amounts of rainfall were recorded--more than 1200 mm
on the heights of the volcano and from 200 to 500 mm over the northern
and eastern coastal areas. There was no real damage associated with
the rains which were very welcome as the season had been exceptionally
dry up to that point. There were two fatalities due to drowning in a
river.
(A special thanks to Arvind Mungur and Philippe Caroff for passing
along information on the effects of Davina.)
Tropical Depression E39899 (TC-29S)
11 - 21 March
------------------------------------
A weak tropical disturbance was noted on 11 Mar about 950 nm east-
southeast of Diego Garcia. The system drifted initially to the west-
northwest and then moved on a more westerly course for several days.
By 16/0000 UTC the system had attained sufficient organization that
La Reunion upgraded it to a tropical depression about 350 nm southeast
of Diego Garcia. JTWC initiated warnings 24 hrs later when it was
centered about 400 nm south-southeast of Diego Garcia. The depression
drifted slowly westward, then turned more to the southwest and
eventually south, losing its identity by 21/0000 UTC about 400 nm
east of Rodrigues Island.
According to remarks in the JTWC warnings, satellite intensity
estimates generally ranged from 25 to 35 kts (1-min MSW) on 17 Mar
when the system was at its peak organization. Microwave imaging data
indicated a fairly well-defined circulation center with some banding.
La Reunion's satellite assessments reached Dvorak T2.5 on 17 and 18
Mar, so the peak 1-min MSW of 35 kts assigned by JTWC seems likely.
Since La Reunion utilizes a conversion factor of 0.8 to adjust the
Dvorak scale to 10-min avg maximum sustained winds, a tropical system
must reach a solid T3.0 to be considered a tropical storm.
***********************************************************************
AUSTRALIAN REGION (AUG) - From Longitude 90E Eastward to Longitude 160E
Activity for March: 2 tropical LOWS (depressions)
3 severe tropical cyclones (hurricane intensity)
The primary sources of information for Australian Region tropical
cyclones are the warnings and bulletins issued by the three TCWC's
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. Additionally,
some information came from the Monthly Report of the RSMC at Darwin,
Northern Territory. References to sustained winds should be
understood as being based on a 10-min averaging period unless
otherwise noted.
Mr. Matthew Saxby, a tropical cyclone enthusiast from Queanbeyan,
New South Wales, Australia, assists me with collecting information
and preparing tracks for tropical cyclones in the Australian Region.
Some of the information contained in the narratives is based upon
information forwarded to me by Matthew. A special thanks to Matthew
for his assistance.
Australian Region Activity for March
------------------------------------
All the Australian Region activity during March occurred in the
Southeastern Indian Ocean off the western coasts of the continent
and was punctuated by three severe tropical cyclones of hurricane
intensity--two of these very intense indeed. One cyclone, Vance,
was responsible for the highest wind gust ever measured in Australia
as well as extensive damage. Two weaker tropical LOWS (depressions)
occurred also during the month. One of these (numbered TC-26S by
JTWC) had some indications of 35-kt winds and will be discussed
separately below. The other tropical LOW was quite short-lived, being
in warning status from Perth only on 20 and 21 Mar. This system formed
southwest of Java, or about 425 nm south-southwest of Christmas Island,
and remained quasi-stationary for a couple of days before weakening.
JTWC never issued any warnings on this weak LOW.
Tropical LOW (TC-26S)
28 February - 27 March
----------------------
This tropical disturbance remained rather weak, but was very
tenacious, existing as an identifiable LOW for almost a month. The
disturbance was initially identified in JTWC Tropical Weather Outlooks
as early as 28 Feb south of the island of Timor, but the system
moved and/or re-formed to the west during succeeding days and was
located about 175 nm south of Cocos Island when JTWC issued the
first warning on 7 Mar at 0600 UTC. Perth issued gale warnings on
the LOW on 7 and 8 Mar before it crossed 90E into the La Reunion/
Mauritius AOR. During the time it was in warning status by Perth
and JTWC the system was moving quite rapidly westward at speeds of
almost 20 kts at times. A sketch of the subsequent history of this
disturbance after it moved west of 90E can be found in the section
of this summary covering the South Indian Ocean basin.
Based upon the remarks in JTWC warnings, satellite intensity
estimates for this system generally reached about 30 kts 1-min avg.
There were some indications from scatterometer data of winds to
35 kts within the circulation, but also there appeared to be multiple
circulation centers without a single well-defined low-level
circulation. Vertical shear and cold air entrainment from the south
prevented any further development of this disturbance.
Severe Tropical Cyclone Elaine (TC-28S)
14 - 20 March
----------------------------------------
A LOW was noted within the monsoon trough in the Timor Sea on
12 Mar. The system drifted westward, and with low vertical shear and
a favorable outflow pattern, began to intensify quite rapidly on the
16th. JTWC initiated warnings at 1800 UTC with the developing
depression located about 425 nm north of Onslow, and Perth issued the
first warning three hours later. By 17/0000 UTC the LOW had become
Tropical Cyclone Elaine with 50-kt MSW about 400 nm north-northwest
of Onslow. Initially moving southwestward, Elaine turned to more of
a south-southwestward track as it reached its peak intensity of 75 kts
at 1600 UTC on 17 Mar when located about 350 nm northwest of Onslow.
(JTWC, apparently following the highest of several Dvorak ratings,
reported peak 1-min MSW at 100 kts at 0400 UTC on the 18th.)
After reaching its peak intensity, Tropical Cyclone Elaine began to
move southward into a very high vertical shear environment which led
to its rapid weakening. The cyclone moved on a course slightly east
of due south and roughly parallel to the Western Australian coastline.
By 19/1000 UTC the MSW had dropped to 45 kts as the weakening Elaine
passed about 150 nm west of Carnarvon. Elaine was downgraded to a
tropical LOW later that day (although some 40-kt gales were still
present in the southern semicircle), and by 0400 UTC on 20 Mar the
system had moved southeastward and inland near Geraldton where it
subsequently dissipated.
Severe Tropical Cyclone Vance (TC-30S)
16 - 24 March
---------------------------------------
As Tropical Cyclone Elaine was developing farther to the west,
another LOW was identified within the persistent monsoon trough
along the northern Australian coast. This new system was centered
about 100 nm east-northeast of Darwin early on 16 Mar and drifted
westward into the Timor Sea as it slowly became better organized.
By 18/0330 UTC the system had become Tropical Cyclone Vance about
325 nm west of Darwin. Vance started to move west-southwestward
under the influence of a subtropical ridge to its southeast. The
cyclone reached severe tropical cyclone (hurricane) intensity at
1000 UTC on 19 Mar when it was centered about 250 nm north-northwest
of Broome. Later that same day the cyclone began to move more to
the southwest as it continued to intensify.
Severe Tropical Cyclone Vance initially reached its peak intensity
of 915 mb estimated central pressure and 110 kts MSW by 2200 UTC on
20 Mar and maintained this strength until landfall near 0000 UTC on
22 Mar. JTWC's estimated peak 1-min MSW of 125 kts is in excellent
agreement with Perth's, apparently being based on a Dvorak rating
of T6.5 (127 kts). The Australian TCWC's use a conversion factor
of 0.88 to reduce the nominal Dvorak 1-min MSW values to an equivalent
10-min MSW value.
The center of this very intense cyclone made landfall near the
mouth of the Exmouth Gulf around 22/0000 UTC, moving southward at
about 15 kts. Near the time of landfall Vance displayed a large
eye about 30 nm in diameter. The center of Vance passed between
Learmonth and Onslow, passing about 40-45 nm west of Onslow. After
moving inland the cyclone gradually turned to a south-southeasterly
and later southeasterly course which carried it across the continent
and out into the Great Australian Bight as a still rather potent
system. Around 0600 UTC on 23 Mar the center of Vance was inland
roughly 325 nm east-northeast of Perth and the advices from Perth
were still forecasting peak gusts well above gale-force. After
emerging into the Bight the remnants of Vance continued on an east-
southeasterly course which carried it just southwest of Adelaide
around 0500 UTC on 24 Mar and to near northwestern Tasmania by
1800 UTC, after which time it merged with a frontal system. Winds to
gale-force were felt along the coastlines of South Australia, Victoria,
and Tasmania as the former tropical cyclone swept by.
Exmouth bore the brunt of Vance's damage with 112 homes destroyed,
224 damaged, and a trailer park flattened. Power lines and trees
were toppled, and the very high seas and tides caused severe erosion
of the beachfront at Exmouth. As the decaying cyclone swept south-
ward, heavy rains caused flooding in the southern goldfields, and
the main highway and rail links to the eastern states were both cut
by floodwaters. Fortunately, no casualties were reported due to
the storm.
Tropical Cyclone Vance became notable for producing the highest
wind gust ever recorded on the Australian mainland. At the Learmonth
Meteorological Office, 35 km south of Exmouth, a wind gust of 145 kts
(267 km/hr) was recorded shortly before midday on 22 Mar. The
previous record Australian gust of 141 kts (259 km/hr) was recorded
at Mardie, Western Australia, in February, 1975, in association with
Cyclone Trixie. At Onslow, 80 km to the east of Vance's track, a peak
gust of 95 kts (174 km/hr) was recorded.
(Some of the information in the preceeding two paragraphs was
taken from a report on Tropical Cyclone Vance prepared by the Perth
TCWC and made available on the Bureau of Meteorology's website.)
Severe Tropical Cyclone Frederic (TC-31S)
21 March --->
------------------------------------------
Another LOW within the monsoon trough was noted in the Darwin
Tropical Weather Outlook as early as 21 Mar. By 24 Mar the LOW was
off the north Kimberley coast and under a favorable upper-air pattern
with weak vertical shear. As the system continued tracking to the
west-southwest it began to slowly develop. Both Perth and JTWC
initiated warnings on the LOW on 26 Mar when it was centered about
550 nm north of Onslow. Under the steering influence of a subtropical
ridge to the south-southeast the system continued moving on a
west-southwesterly course as it slowly intensified, being upgraded to
Tropical Cyclone Frederic at 2200 UTC on 27 Mar when it was located
about 325 nm southeast of Christmas Island.
By 29/1600 UTC Frederic was upgraded to a severe tropical cyclone
(hurricane). The cyclone was by now moving on a track that was
slightly south of due west. Frederic reached its peak intensity of
110 kts MSW and 915 mb central pressure at 1600 UTC on 31 Mar as it
was approaching the boundary between the Perth and Mauritius AORs.
About this time the cyclone moved from the influence of one HIGH to
another HIGH within the subtropical ridge into a zone of increased
vertical shear. (It was such a "transfer" as this from one HIGH cell
to another that led to the marked reduction in intensity of Atlantic
Hurricane Georges last September as it approached the Lesser Antilles.)
A slight weakening was beginning to take place as Frederic entered
the South Indian Ocean basin and was renamed Evrina. The conclusion
of the history of Tropical Cyclone Frederic/Evrina will be reported
in the April summary.
Just how intense did Frederic become? JTWC created somewhat of a
stir late on 31 Mar when they reported the 1-min MSW to be 155 kts.
This was based on a 31/2330 UTC satellite bulletin from JTWC giving
Frederic a Dvorak number of T7.5. However, a satellite bulletin from
the Air Force Global Weather Central at the same time rated Frederic
at T6.5 (127 kts 1-min avg). Perth and La Reunion were also
assessing the cyclone's Dvorak rating at T6.5. In a private e-mail,
Jim Parsons, a Typhoon Duty Officer at JTWC, informed me that the peak
MSW will be scaled back to T7.0--140 kts. When several different
satellite analysts all agree to within one-half T-number, this is
very good agreement indeed.
ADDENDUM for February Tropical Cyclone Summary
Tropical Cyclone Rona
----------------------------------------------
Tropical Cyclone Rona struck the northeastern Queensland coast on
12 Feb causing considerable damage. (See the February Summary for more
details.) Jeff Callaghan of the Brisbane TCWC has sent me some
additional details on Tropical Cyclone Rona. Landfall occurred just
to the north of Cow Bay which is near the mouth of the Daintree River.
Significant wind damage extended from Newell Beach to Cape Tribulation
with major damage between Cape Kimberley and Cape Tribulation. Some
trees in the Cape Tribulation area which survived a 1934 cyclone were
felled by Rona. Major flooding and damage to crops and infrastructure
occurred between Townsville and Cairns.
The question was raised in last month's summary as to whether or not
Rona reached hurricane intensity. Cyclone Rona indeed reached
hurricane intensity. An automatic weather station at Low Isle recorded
a 10-min avg wind of 71 kts with a peak gust of 85 kts. The same
station (which was not in the eye) recorded a minimum pressure of
983 mb. A 1-m storm surge was recorded at Port Douglas (at low tide)
and a 1.4-m surge was recorded at the mouth of the Mossman River.
These sites were south of the maximum wind zone where the largest storm
surge would be expected.
(A special thanks to Jeff for forwarding the information to me.)
***********************************************************************
SOUTHWEST PACIFIC (SWP) - South Pacific Ocean East of Longitude 160E
Activity for March: 1 tropical depression
1 tropical cyclone of hurricane intensity
NOTE: Most of the information presented below was taken from the
operational warnings and advisories issued by the Fiji TCWC at Nadi
and from the Monthly Summary for March prepared by Alipate
Waqaicelua, Principal Scientific Officer and Chief of the forecasting
group. A special thanks to Alipate for sending the summary to me.
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.
Southwest Pacific Activity for March
------------------------------------
The month of March was less active in the Southwest Pacific basin
than February had been, producing only one named tropical cyclone and
a tropical depression. Neither of these systems significantly affected
any populated areas and no damage reports have been received to date.
Tropical Disturbance 21F was a weak, short-lived disturbance which
formed on 28 Mar about 180 nm northeast of Niue. This system moved
slowly southward in a hostile shearing environment and never attained
tropical depression status.
Tropical Cyclone Hali (TD-19F / TC-27P)
11 - 19 March
----------------------------------------
A tropical disturbance was first identified around 0000 UTC on 11
Mar, embedded in an active SPCZ between the Southern Cooks and French
Polynesia, and moving slowly southwestward. By 11/0600 UTC the
system had become a tropical depression about 300 nm east of Aitutaki
Island. Still under the influence of diurnal effects and significant
vertical shear, the depression developed slowly as it drifted toward
the Southern Cooks. The center drifted between the islands of
Manuae and Takutea early on 12 Mar. The depression was located under
a 250-mb ridge and convective organization had improved, but there
was still some shearing and the low-level center was partly exposed.
By 12/1800 UTC Dvorak numbers had reached T3.0 and the depression was
upgraded to Tropical Cyclone Hali about 90 nm north-northeast of
Rarotonga.
Hali continued on a general westerly course for the next three days
as it continued to increase in intensity. The westernmost point in
Hali's track was reached around 1200 UTC on 15 Mar when the storm was
centered about 325 nm east-southeast of Niue Island or 275 nm west of
Rarotonga. The cyclone turned rather abruptly to the south at this
time due to the effects of an approaching upper trough. A cloud-filled
eye had briefly appeared at 14/0000 UTC on visible imagery but had
not persisted. It reappeared at 16/0000 UTC; consequently, Hali was
upgraded to hurricane intensity for a 12-hour period. After 1200 UTC
the cyclone was beginning to weaken due to increasing shear and by
virtue of its moving into cooler waters. The weakening system moved
generally southward through 17/1200 UTC after which it turned to the
east-southeast. Increasing shear, as well as the disruptive effects
of a developing tropical depression to the east (TD-20F), caused Hali
to weaken rapidly, and the system was downgraded to a depression at
1200 UTC on the 18th when it was located roughly 200 nm south-southwest
of Rarotonga. There was no convection near the center and the weak
LOW, caught up in the low-level steering field, drifted into
Wellington's AOR after 19/0000 UTC.
There were two interesting aspects of Tropical Cyclone Hali which
need to be mentioned. One, this system was a very small, midget
tropical cyclone. At its greatest intensity gale-force winds
(>33 kts) were estimated to extend out only 50-60 nm from the center,
and storm-force winds (>47 kts) were confined to within about 25 nm
of the center. Secondly, NPMOC's intensity assessment of Hali was
much less than Nadi's. Except for the second warning early in Hali's
life when the 1-min MSW was estimated at 50 kts, the highest reported
MSW by NPMOC was 45 kts, even when Nadi was reporting a 10-min MSW
of 65 kts, which would be approximately equivalent to a 75-kt 1-min
MSW. This raises the question of whether or not the very small size
of Hali had something to do with this disagreement in reported MSW.
Alipate's summary mentions that "the size of this system (midget) did
not allow Nadi to adopt the normal classification scale for normal-
sized storms".
Tropical Depression (TD-20F)
16 - 18 March
-----------------------------
The TCWC at Nadi first noted a tropical disturbance on 13 Mar
located to the northeast of French Polynesia and drifting
southwestward. The upper-level environment was not particularly
favorable for development and deep convection was confined to the
northern quadrant. The system was elevated to tropical depression
status at 15/0600 UTC, and the first gale warning was issued at
16/2100 UTC when the center was about 150 nm east of Mauke Island
in the Southern Cooks, or roughly 350 nm west-southwest of Tahiti.
The depression moved southward, almost perfectly straddling the
155th meridian of west longitude and passing 170 nm east of Mangaia
in the Southern Cooks at 17/1200 UTC. Some convective spiral bands
were noted on the 17th, but were detached from the center which was
exposed to the southwest of the deep convection. The depression
continued southward and moved into Wellington's AOR at a point about
350 nm southeast of Rarotonga.
There were a couple of ship reports of gale-force winds associated
with this system. At 15/2100 UTC ship FNIK reported northerly winds
to 40 kts and a minimum pressure of 1005.9 mb about 60 nm northeast
of the center. At 16/2100 UTC ship P3SL7 reported northerly winds
also to 40 kts and a minimum pressure of 1006.3 mb about 90 nm
northeast of the depression's center. In both cases these winds
were believed to be associated with local squalls.
***********************************************************************
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: mar99.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: mar99.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, some of the preliminary storm reports 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)
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Document: summ9903.htm
Updated: 18th March 2008 |
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