[Index]
Monthly Global Tropical Cyclone Summary March 2001
[Summaries and Track Data] [Prepared by Gary Padgett]
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Cyclones
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Monthly Global Tropical Cyclone Summary March 2001 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
MARCH, 2001
(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.)
***********************************************************************
MARCH HIGHLIGHTS
--> Tropics quiet/unusual subtropical (possibly tropical) cyclone
affects eastern Australia
***********************************************************************
***** Feature of the Month for March *****
Western Hemisphere Tropical Cyclone Names for 2001
Tropical cyclones in the Atlantic Ocean, Gulf of Mexico, and
Caribbean Sea are assigned names by the Tropical Prediction Center/
National Hurricane Center in Miami, Florida. A separate alphabetical
set of alternating male/female names is used each year with the name
of the first tropical storm beginning with the letter "A". Names are
repeated every six years. The names of hurricanes which cause a lot
of damage and/or fatalities are usually retired from the list with
another name of the same alphabetical rank and gender replacing it.
Following the 2000 season, the name Keith was retired and replaced
with Kirk in the list for 2006.
The list of names for 2001 is the same one used during the great
hurricane season of 1995 when nineteen tropical cyclones reached
tropical storm intensity--the most seen in the Atlantic since 1933.
Four names were retired following that season due to their destructive
effects--Luis, Marilyn, Opal and Roxanne--and have been replaced in
the list with the names Lorenzo, Michelle, Olga and Rebekah.
TPC/NHC also has warning responsibility for the Eastern North
Pacific Ocean from the west coast of Mexico out to longitude 140W.
Six separate alphabetical sets of names are used for this basin in
the same manner as in the Atlantic. Following the 1995 season,
Ismael was retired and replaced in the list for 2001 with Israel.
The Central Pacific Hurricane Center, located in Honolulu, has
tropical cyclone warning responsibility for that portion of the North
Pacific Ocean lying between longitudes 140W and 180. The majority of
the tropical storms and hurricanes seen in that region are visitors
from east of 140W, but on the average about one tropical storm forms
in the Central Pacific each year, and when this happens, the storm is
given a Hawaiian name. The list consists of four sets of twelve
names each, using only the letters of the Hawaiian alphabet. All the
names are used--the first storm to form in a given year is assigned
the next available name on the list. Two tropical storms were named
by CPHC in 2000, Upana and Wene, but prior to that, the last previous
Central Pacific storm had been Paka in December of 1997.
Names for 2001 are (** indicates name has already been assigned):
ATLANTIC EASTERN PACIFIC CENTRAL PACIFIC
Allison Lorenzo Adolph ** Manuel Alika
Barry Michelle Barbara Narda Ele
Chantal Noel Cosme Octave Huko
Dean Olga Dalila Priscilla Ioke
Erin Pablo Erick Raymond Kika
Felix Rebekah Flossie Sonia Lana
Gabrielle Sebastien Gil Tico Maka
Humberto Tanya Henriette Velma Neki
Iris Van Israel Wallis Oleka
Jerry Wendy Juliette Xina Peni
Karen Kiko York Ulia
Lorena Zelda Wali
***** Additional Feature *****
Charts of Monthly Net Tropical Cyclone Activity (NTC)
The idea for these charts originated with Eric Blake's tropical
cyclone forecast for the month of August, 2000, included in the
August update to the CSU 2000 Atlantic seasonal forecast. Eric
made reference to the percentage of the total NTC which was normally
contributed by the month of August, so I became interested in
calculating such a figure for all the months for the Atlantic and
Northeast Pacific (NEP) basins.
In the discussion and in the charts, the following abbreviations
are used. These are the same ones used by Dr. Bill Gray and the
CSU forecast team, and the complete definitions can be found on
the CSU website in any of the Atlantic seasonal forecasts archived
there: http://tropical.atmos.colostate.edu/forecasts/>
NS - named storm (MSW > 33 kts, whether actually named or not)
H - hurricane (MSW > 63 kts)
IH - intense hurricane (MSW > 95 kts)
NSD - named storm day
HD - hurricane day
IHD - intense hurricane day
NTC - net tropical cyclone activity (avg of other 6 parameters)
For the Atlantic statistics I used the period 1950-2000. Even
though aerial reconnaissance of Atlantic cyclones began in 1944,
I began with 1950 since that year is the beginning point of Dr. Gray's
and the CSU forecast team's NTC calculations. For the NEP basin I
utilized the period 1971-2000. Extensive aerial reconnaissance of
these cyclones was performed during the 1971-1973 seasons before
being curtailed following the Arab oil embargo of late 1973. By 1974
the first edition of the Dvorak method had been developed and was
beginning to be used, so the MSW values can be considered somewhat
reliable from that point onward.
Calculating overall seasonal statistics for a TC basin presents no
problem, but when dissecting a season temporally some decisions have
to be made. Some definitions and procedures I followed include:
(1) A month was defined as beginning at 0000Z on the 1st day of the
month and ending at 1800Z on the final day of the month.
(2) The "days" parameters (NSD, HD, IHD) were accumulated for each
exact month per the definition in (1) above. A given storm or
hurricane day was counted in only one month--the month of origin had
no bearing on these parameters.
(3) The other main issue was how to count intermonthly cyclones for
the NS, H, and IH tallies. I decided that a given storm/category
should count in only one month; i.e., when the monthly totals are
added up, they should equal the totals for the season. For the NS
parameter a storm is counted in the month in which winds initially
reached 34 kts (or higher) and the storm type was tropical. A
similar procedure was used for the H and IH parameters. Admittedly
this can lead to some unusual-looking statistics at times. For
instance, Major Hurricane Keith of 2000 was named on 29 September,
reached hurricane intensity on 30 September, and winds reached 100 kts
at 0000Z on 1 October. Therefore, Keith is counted as a September
NS and H, but as an October IH. Similarly, Major Hurricane Opal of
1995 is counted as a September NS, but as an October H and IH.
Northeast Pacific Hurricane Ekeka in 1992 is counted as a January NS
and H but as a February IH. Since no other tropical cyclones
occurred in February during the period under consideration, February
is shown as having no NS or H but one IH. Similarly, in the Atlantic
basin, no cyclones began in January, but the month nonetheless has
some NTC due to Hurricane Alice, which originated and reached
hurricane intensity in December, 1954, but remained active until
5 January, 1955.
Another issue which needed to be addressed was the well-known
upward bias in Best Track MSW values for the Atlantic basin prior to
around 1970. Following the rule which Chris Landsea gave me years
ago, for the years 1950-1970, any MSW value of 100-115 kts was reduced
by 5 kts. Any MSW value of 120 kts or greater was reduced by 10 kts.
However, there were a few cases where I excepted this rule based upon
normal maximum wind/minimum pressure relationships--Carol of 1953,
Janet of 1955, Hattie of 1961, Camille of 1969--to name a few. Also,
I upped the MSW for Hurricanes Daisy and Helene of 1958 based upon the
central pressures and the MSW as given by Dunn & Miller in _Atlantic
Hurricanes_. It should be mentioned that there are quite likely some
MSW biases in the NEP Best Track file, but I did not attempt to correct
any of these as I had no guidance for doing so.
One final item--the various statistics for the NEP basin include
all systems which reached the various intensity levels east of
longitude 180, but the "days" parameters are accumulated only for the
time which a given system spent east of 180. A system which began east
of 180 but reached H or IH intensity west of 180 is counted only as a
NS (e.g., Paka of 1997). This is just my preference--there are other
methodologies which are equally valid. The Central North Pacific
(CNP) between 140W and 180 has such a low incidence of TC activity,
especially formations, that it is difficult to consider it as a
separate basin. A majority of the NTC in the CNP is generated by
storms originating east of 140W, and while most TCs originating in the
CNP do not affect Hawaii, the two destructive Hawaiian hurricanes of
the past three decades (Iwa and Iniki) reached tropical storm intensity
in the CNP and shouldn't be ignored. On the other hand, I did not want
to skew NEP basin statistics by including the NWP portions of such
storms as Ruby of 1972 and Oliwa and Paka of 1997 which formed just
east of the Dateline but went on to become long-lived and/or very
intense typhoons in the NWP basin.
Atlantic Basin Monthly NTC Chart
--------------------------------
Month NS H IH NSD HD IHD NTC
JAN 0 0 0 4.5 3.5 0 0.08
FEB 1 0 0 1.5 0 0 0.04
MAR 0 0 0 0 0 0 0.00
APR 0 0 0 0 0 0 0.00
MAY 5 2 0 18.5 6.25 0 0.49
JUN 26 10 2 71.5 13.25 0.75 2.42
JUL 41 17 1 121.25 32.25 0.5 3.74
AUG 135 79 30 603.25 296.5 63.25 25.29
SEP 173 121 63 1105 628 153.75 47.22
OCT 83 55 16 454.5 226.25 38.25 16.65
NOV 24 17 3 114.75 39.25 4.25 3.74
DEC 3 2 0 10.75 3.75 0 0.33
TOTAL 491 303 115 2505.5 1249 260.75
AVG 9.63 5.94 2.25 49.13 24.49 5.11
Northeast Pacific Basin Monthly NTC Chart
-----------------------------------------
Month NS H IH NSD HD IHD NTC
JAN 1 1 0 3.25 2 0 0.15
FEB 0 0 1 3 2.25 0.5 0.21
MAR 1 0 0 1 0 0 0.04
APR 0 0 0 0 0 0 0.00
MAY 14 7 0 44.5 9.75 0 1.38
JUN 66 36 14 246.5 93.25 26 11.07
JUL 114 62 35 501.75 228.25 72 23.80
AUG 121 73 34 638 255.25 58 25.16
SEP 106 66 34 514.75 251.5 74.25 24.27
OCT 57 33 19 278.25 131.5 39 12.88
NOV 11 3 0 28.5 4.75 0 0.84
DEC 2 1 0 7.5 1 0 0.20
TOTAL 493 282 137 2267 979.5 269.75
AVG 16.43 9.40 4.57 75.57 32.65 8.99
The differences between the two basins in the seasonal pattern of
activity are striking. The Atlantic season is sharply-peaked with
almost half of the NTC occurring in the month of September alone; the
three-month period of August through October accounts for almost 90%
of the annual NTC. By way of contrast, the Northeast Pacific basin's
seasonal pattern of activity does not reach such a sharp peak, but
exhibits a plauteauing of NTC over the months of July, August, and
September with each month contributing about 25% of the annual NTC.
June and October make up the majority of the remaining amount.
One interesting and somewhat surprising fact apparent in the
Atlantic NTC chart is that July and November have the same level of
activity. November lags behind June and July in number of named
storms, the parameter usually used to judge activity, but has (at
least in recent decades) seen considerably more hurricane and intense
hurricane activity. Atlantic intense hurricanes are almost always
confined to the peak months of August, September, and October; the
only exceptions during the previous half-century are:
June - Audrey (1957), Alma (1966)
July - Bertha (1996)
November - Greta (1956), Kate (1985), Lenny (1999)
***********************************************************************
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: 1 tropical cyclone **
** - no warnings were issued on this system by JTWC or IMD
Tropical Cyclone "Omicron"
10 - 15 March
--------------------------
A couple of weeks ago I received from Roger Edson some tracks on
several tropical systems that he felt had been tropical depressions
or tropical storms. One of these systems was a March system in the
eastern reaches of the Bay of Bengal. Roger was for many years in
the U. S. Air Force and was a typhoon forecaster at JTWC for about
seventeen years. He now resides on Guam and is associated with the
University of Guam. Since Roger assigned a 35-kt MSW to the March
system at one point, I have designated it with the Greek letter
"Omicron". Roger's track follows the discussion. I will send an
updated track file for March to the various persons who archive the
summaries and track files on their websites.
JTWC did not issue any warnings nor Formation Alerts on this
disturbance, but it was mentioned for several days in their STWOs
and was given a fair potential for development at one point. The
initial LLCC formed deep in the tropics in the Andaman Sea over
200 nm north of the northern tip of Sumatra on 10 March. Over the
next several days it drifted generally in a north-northwestward
direction. For the first few days of its life the disturbance was
in an area of weak vertical shear and slowly increased in organization.
Roger estimates that winds had reached 25 kts by 12/1200 UTC and 30 kts
by 1200 UTC on the 13th.
The track indicates that the peak intensity of 35 kts was reached
at 14/0000 UTC when the center was located about 275 nm southwest of
Yangan (Rangoon), Burma. Roger's e-mail indicates that he has plenty
of satellite and scatterometer data to support his positions and
intensities. He notes that at 14/0531 UTC KGWC gave a fix on the
system with a CI number of T1.5 (25 kts), but the comments suggested
that the Data T-number was T2.5 (35 kts). As the system moved farther
north, it moved out from under an upper-level ridge axis and into an
area of moderate to strong southwesterly shear and began to quickly
weaken. The final position in the track locates the weakening center
about 100 nm west of Yangan at 1200 UTC on 15 March. Roger's comments
indicate that the system had all but dissipated by the time it made
landfall.
The track for "Omicron" follows:
***********************************************************************
Storm Name: "Omicron" Cyclone Number: None Basin: NIO
(Track provided by Roger Edson)
Date Time Lat Lon Cent MSW MSW Remarks
(GMT) Press 1-min 10-min
(mb) (kts) (kts)
-----------------------------------------------------------------------
01 MAR 10 0000 9.0 N 96.0 E 15
01 MAR 10 1200 9.5 N 95.5 E 1007 15
01 MAR 11 0000 10.0 N 95.0 E 15
01 MAR 11 1200 10.7 N 94.0 E 1006 20
01 MAR 12 0000 11.5 N 93.0 E 20
01 MAR 12 1200 12.0 N 93.0 E 1004 25
01 MAR 13 0000 12.5 N 93.0 E 25
01 MAR 13 1200 13.0 N 93.0 E 1004 30
01 MAR 14 0000 13.5 N 93.0 E 35
01 MAR 14 1200 14.7 N 92.8 E 1004 30
01 MAR 15 0000 16.0 N 92.5 E 30
01 MAR 15 1200 16.5 N 94.5 E 1004 25
Note: The central pressure estimates were taken from the daily STWOs
issued by JTWC.
***********************************************************************
SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E
Activity for March: 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, which is the RSMC for the Southwest 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 tracks file
some position comparisons have been made with JTWC's positions, and
warnings from JTWC were used as a source of 1-min avg MSW estimates.
(A special thanks to Patrick Hoareau of Rennes, France, for sending
me the operational track for Tropical Cyclone Dera already typed in
the correct format.)
Southwest Indian Ocean Tropical Activity for March
--------------------------------------------------
After a completely quiet February, save for one tropical depression,
the Southwest Indian Ocean became active again, but only briefly.
Only one tropical storm formed, but like all the others so far this
season, reached tropical cyclone (hurricane) intensity. Dera formed
in the upper tropics in the Mozambique Channel from a persistent
disturbance which had drifted southward for several days from the
vicinity of northern Madagascar. The cyclone did not become as
intense as the January cyclones had been, but did reach a rather
respectable intensity of 75 kts at its peak. Fortunately, Dera
remained at sea and did not directly affect any land areas.
Tropical Cyclone Dera (TC-15S / MFR #8)
5 - 13 March
----------------------------------------
A. Origins
----------
On 4 March, at 1800 UTC, a STWO issued by JTWC mentioned that an
area of convection was developing approximately 155 nm northeast of
the northern tip of Madagascar. A recent QuikScat pass had revealed
the presence of a LLCC over the western extension of the Near
Equatorial Trough, and a ship located just west of the LLCC had
reported southerly sustained winds of 8 kts with a pressure of
1008.2 mb. Convection was increasing in coverage under pronounced
diffluent flow over the region. By the 5th the disturbance had drifted
southward to a point about 90 nm northeast of Madagascar's northern
tip, and visible imagery depicted well-defined low-level cloud lines
with deep convection displaced to the northwest of the center. JTWC
upgraded the development potential to fair while MFR La Reunion began
issuing bulletins on Tropical Disturbance #8 at 1200 UTC.
The LLCC exhibited less definition on the 6th as it continued to
drift in a general southerly direction. MFR positioned the weak center
inland over northern Madagascar while JTWC kept it west of the island
over the Mozambique Channel. CIMSS wind shear products indicated that
the disturbance was in an environment of moderate vertical shear. MFR
suspended bulletins on the system for 24 hours after 06/0600 UTC.
On 7 March both MFR and JTWC relocated the LLCC over water west of
Madagascar and MFR resumed issuing bulletins on the disturbance. A
new burst of convection had appeared just north of the LLCC, and a
200-mb analysis indicated that the subtropical ridge extended over the
region. During the 8th the disturbance continued to drift southward
over the Channel while gradually consolidating its convection. JTWC
initiated warnings on TC-15S with 30-kt winds (1-min avg MSW) at
0000 UTC on 9 March when the center was estimated to be about 400 nm
west-southwest of Majunga on the west coast of Madagascar, or about
300 nm east-northeast of Beira, Mozambique. Six hours later MFR
upgraded the disturbance to a tropical depression with maximum 10-min
avg winds of 30 kts.
B. Track and Intensity History
------------------------------
By 1200 UTC on 9 March visible imagery indicated that the depression
was intensifying rapidly with the early stages of a developing eye
clearly evident. MFR upgraded the depression to Tropical Storm Dera
at 1200 UTC with the maximum sustained winds estimated at 50 kts--quite
a jump from 30 kts six hours earlier. Dera was centered about 325 nm
east-southeast of Beira, Mozambique, at the time, moving slowly south-
ward. The storm intensified rapidly into a tropical cyclone with winds
reaching 70 kts by 10/0600 UTC when it was located about 175 nm west
of Tulear in southwestern Madagascar. Dera reached its peak intensity
of 75 kts at 1200 UTC on 10 March and maintained it for 24 hours.
The cyclone moved slowly southward in the Mozambique Channel, passing
due west of the southern tip of Madagascar around 10/1800 UTC.
By 0000 UTC on 12 March Tropical Cyclone Dera was located roughly
525 nm east of Durban, South Africa, and was beginning to accelerate
to the south-southeast. By 1200 UTC Dera's forward motion had
increased to 33 kts as it began to undergo extratropical transition,
the convection having weakened considerably. At 13/0000 UTC the storm
was racing southeastward at 54 kts and appeared to have become fully
extratropical with open-cell, cold-air cumulus located northwest of the
center. MFR issued its last tropical cyclone bulletin on the still
70-kt storm at 12/1200 UTC, and JTWC wrote their final warning at
13/0000 UTC, placing the center of former Tropical Cyclone Dera about
1300 nm south-southwest of Reunion.
Tropical Cyclone Dera reached its estimated peak intensity of 75 kts
(10-min avg) at 10/1200 UTC and remained at that intensity through
11/0600 UTC. The estimated minimum central pressure was 960 mb for
the same period.
C. Meteorological Aspects
-------------------------
About the time that Dera was named (1200 UTC on 9 March), synoptic
reports from Europa Island (WMO 61972) indicated 30-kt sustained winds
with upper-air reports of 40-kt winds at 600 m. Satellite imagery
revealed a good banding feature east of the center, and a 200-mb
analysis and water vapor imagery showed a trough west of the storm
with anticyclonic flow over the eastern semicircle enhancing outflow.
A poleward-oriented mid-level ridge east of Madagascar was the primary
steering influence for Dera.
The center of Dera passed just to the east of Europa Island between
09/1800 UTC and 10/0000 UTC. A ragged 30-nm diameter eye was visible
with a dry slot evident east of the eye. Philippe Caroff reported
that as the leading portion of the eyewall passed over Europa, peak
gusts of 84 kts were recorded. The minimum pressure recorded in the
eye was 973 mb, and as the trailing portion of the eyewall passed over
the island, 10-min mean winds of 54 kts were recorded with the peak
gust reaching 74 kts.
After Dera had become extratropical, the system passed just west of
Crozet Island (46.5S, 51.0E). Philippe passed along a report from the
AWS maintained by MFR on the island. A maximum sustained wind of
53 kts was recorded with a peak gust of 72 kts--the lowest SLP was
975 mb. During the two hours following the minimum pressure the
temperature rose around 5 to 6 deg C to a peak of 17.4 C. Even though
satellite imagery depicted a classic mid-latitude frontal cyclone, this
temperature rise indicates the presence of a residual warm core.
D. Comparisons Between MFR and JTWC
-----------------------------------
During the warning phase of Tropical Cyclone Dera, center position
coordinates between the two warning centers were in excellent
agreement. JTWC's intensity estimates generally ran lower than those
from MFR with JTWC reporting a peak 1-min avg MSW of 70 kts at the
time MFR was estimating the maximum 10-min avg winds to be 75 kts.
Interestingly, JTWC's peak MSW estimate of 75 kts (at 12/0000 UTC) came
after MFR had begun to weaken the cyclone. The remarks in the JTWC
warning indicated that this value was based CI estimates of 90 and
102 kts, recent microwave imagery, and extratropical transition of the
system.
E. Damage and Casualties
------------------------
During the formative stages of Dera heavy rains and gusty winds
affected the northern Mozambican province of Nampula. Press reports
indicated that two persons died and one was seriously injured. Dozens
of homes and boats were destroyed and many roads rendered impassable.
***********************************************************************
NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E
Activity for March: 1 tropical LOW
Northwest Australia/Southeast Indian Ocean
Tropical Activity for March
------------------------------------------
No named tropical cyclones occurred in Southeast Indian waters off
Western Australia during March, but gale warnings were issued by Perth
for one tropical LOW around mid-month which was forecast to possibly
develop into a tropical cyclone. The first warning at 16/0400 UTC
located the LOW's center about 40 nm north-northeast of Christmas
Island. The system drifted slowly westward over the next day or so
and the final warning on the weakening system, issued at 0900 UTC on
the 17th, placed the center about 175 west-northwest of Christmas
Island. No actual reports of gale-force winds were mentioned in any
of the warnings.
***********************************************************************
NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E
Activity for March: 1 subtropical (possibly tropical) cyclone
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>
Carl Smith, a cyclone enthusiast who lives on Queensland's Gold
Coast, has a website which contains a great amount of information on
tropical cyclones. The URL is: http://www.ace-net.com.au/~carls/>.
Following is a URL where satpic animations and maps can be
found for the subtropical LOW:
http://cyclones.www9.50megs.com/2001/SubTCDonald.html>
Northeast Australia/Coral Sea
Tropical Activity for March
----------------------------
A low-pressure system developed in the subtropics off the East Coast
of Australia and made landfall in northern New South Wales. At land-
fall 10-min avg wind speeds exceeding 50 kts accompanied the LOW,
making it equivalent to a Category 2 tropical cyclone. Late in its
life the LOW displayed some characteristics that are typical of
tropical cyclones. Most of the information given below is taken
directly from a report on the storm prepared by Jeff Callaghan of the
Brisbane TCWC. A special thanks to Jeff for sending me the report and
for permission to use it in this summary. (Note: While this system
obviously generated winds exceeding storm intensity (48 kts), I have
followed Jeff's terminology and refer to it as a LOW. In the title
of his report Jeff refers to the system as a "sub-tropical LOW", and
in another place calls it a "severe tropical LOW". Australia does not
formally use the term "subtropical storm" or "subtropical cyclone", so
I have refrained from doing so here.)
Subtropical LOW
4 - 8 March
---------------
A. Track and History
---------------------
On 4 March a LOW formed in the eastern Tasman Sea near 30S, about
350 nm east-southeast of Brisbane. The system initially moved north-
ward, reaching a point 265 nm east of Brisbane by 05/1800 UTC, thence
moving westward through around 1200 UTC on the 7th when it was located
about 140 nm east of Brisbane. The LOW then took a swing toward the
southwest before turning westward once more and moving onto the coast
of northern New South Wales near Cape Byron around 0800 UTC on 8 March.
During the LOW's early stages, its cloud features were similar to
the early stages of a tropical cyclone, as viewed from satellite
imagery. During the hours immediately preceding landfall, a ragged
eye feature was evident on the northern edge of the cold cloud tops
in infrared imagery. Initially, the system was located over SSTs of
around 24 C, but as it neared the coast it passed over SSTs exceeding
26 C.
B. Meteorological Aspects
-------------------------
(1) Lower Levels
----------------
The initial development of the LOW occurred after a mid- to upper-
level trough system amplified with a resulting cyclonic circulation
extending through much of the troposphere. The LOW moved northwestward
while deepening and by 2300 UTC on 5 March was east of Brisbane. A
large HIGH in the Tasman Sea then moved eastward toward New Zealand,
weakening the pressure gradient, and winds along the coast south of
Brisbane diminished. However, the LOW continued to slowly deepen.
Severe weather and ocean gale warnings were issued for the coast of
southeastern Queensland where large swells, winds and high tides caused
beach erosion and salt water inundation.
An analysis of a satellite image at 0030 UTC on 7 March yielded
Dvorak T-numbers between T3.5 and T4.0--normally associated with a
Category 2 tropical cyclone. However, soon afterward the LOW slowed
its movement toward the coast, and rainbands, which were circulating
around the western flank of the LOW, broke away from the circulation
and moved onshore. This had the effect of giving the system a much
more ragged appearance in satellite imagery such that it no longer
resembled a tropical cyclone.
As the LOW accelerated and moved southwestward into the New South
Wales area of warning responsibility, it began to intensify again.
This was largely due to a large HIGH strengthening and moving into the
Tasman Sea between Australia and New Zealand. This generated a very
intense pressure gradient along the New South Wales coast south of
the LOW. The 1020-mb isobar at this time extended northward to about
latitude 35S while the 996-mb LOW's center was located just equator-
ward of 29S.
(2) Middle and Upper Levels
---------------------------
The LOW at 200-mb formed south of the surface centre and was still
in this location 24 hours after the surface LOW had formed and moved
to the northwest. This upper-level circulation then weakened into a
trough which moved westward, and at 07/2300 UTC the surface circulation
lay under a strongly diffluent 200-mb wind pattern east of the upper-
level trough. At 08/1100 UTC, just after landfall, the surface LOW was
still east of the upper-level trough.
During the 24-hour period from 05/2300 through 06/2300 UTC, the LOW
steadily moved toward the coast while located north of a 500-mb ridge.
Movement slowed by the end of this period as the ridge weakened. About
24 hours later the ridge began to build again and the LOW accelerated
toward the coast. The southward movement of the system appeared to
be due to increased ridging around New Caledonia, resulting in a
stronger meridional contour gradient east of the LOW than to the LOW's
west. The weakening and subsequent strengthening of the mid-level
ridge was easier to discern at 700 mb moreso than at 500 mb. Winds
circulating around the LOW at 700 mb were stronger than at 500 mb--a
good indication that the LOW had a warm core in the middle troposphere.
(3) Thermal Structure
---------------------
The 500-mb thermal pattern indicated that the LOW, while approaching
the coast, lay east of a marked cold 500-mb thermal trough. The LOW
was bringing low-level moist tropical air to the region east of the
cold thermal trough, a pattern which would normally be associated with
cyclogenesis due to baroclinic instability. As the system approached
the coast, it became situated in the 500-mb warm thermal ridge, which
is consistent with the cyclonic circulation weakening between the
700-mb and 500-mb levels.
(4) Wind Observations
---------------------
The Evans Head AWS (located south of the landfall point) recorded
gale-force winds from 0200 through 1000 UTC on 8 March. The strongest
wind of 170/54 kts with gusts to 75 kts was recorded at 0615 UTC as a
strong rainband with enhanced convection moved onto the coast over the
AWS. The eye, still ragged in appearance, lay to the northeast of the
station. A second rainband moved over the area later with southerly
winds of 54 kts, gusting to 70 kts, being recorded at 0652 UTC. The
lowest pressure of 996.6 mb was also recorded at this time. A couple
of hours later, at 0809 UTC, the winds were still blowing at 50 kts,
gusting to 59 kts, as enhanced convection on the southern side of an
ill-defined eye passed over the AWS.
At Vineyard Haven, about 15 km north-northwest of Yamba, winds had
reached gale force by 0330 UTC on the 8th. Between 0400 and 0600 UTC
wind gusts increased to 55 kts. The barometer dropped to around
996-997 mb and remained there from 0700 to 1000 UTC with peak gusts
exceeding 70 kts. Ballina and Byron Bay were near the eye of the LOW,
and winds in general were not as strong as at locations south of the
centre. At 08/0304 UTC Ballina reported sustained winds of 35 kts with
gusts to 49 kts. Byron Bay recorded a MSL pressure of 991.6 mb at
0700 UTC as the LOW's centre approached the coast. Sustained winds
were 240/30 kts with peak gusts reaching 51 kts.
The damaging rainbands which affected the Evans Head area moved up
onto the Alstonville Plateau, affecting the Lismore/Alstonville/McLeans
Ridge area west of Ballina. The major rainband passed through the
McLeans Ridge area around 0415 UTC, bringing gusts of 55-60 kts. The
rainband which had passed over Evans Head around 0615 UTC reached
McLeans Ridge around 0640 UTC with peak gusts estimated at 70 kts.
(5) Rainfall Amounts
--------------------
In the wake of the subtropical LOW, very humid air was advected into
southeastern Queensland by the decaying system while the cold thermal
mid-level trough still lay over the area. On 9 March a line of
thunderstorms became almost stationary over the Queensland Southeast
Coastal District, producing locally heavy rainfall accompanied by
flash flooding from the Sunshine Coast to the Gold Coast. The highest
recorded 24-hour rainfall total was 284 mm at Logan City while several
stations topped 200 mm. Brisbane city recorded 138 mm while Brisbane
Airport measured only 76 mm. Nambour recorded 153.2 mm in the 60-min
period ending at 09/1955 UTC with 90.4 mm falling in 30 minutes and
a 45-min total of 132.2 mm. Holland Park West measured 77 mm of rain
in a 30-min period while Wolffdene (about 10 km south of Logan City)
recorded 232 mm in a three-hour period. Of that amount 203 mm fell
in two hours. Several of these rainfall amounts exceeded the estimated
once-per-century figures.
The above rainfall figures came from some information sent to me
separately by Jeff Callaghan. Michael Bath, who lives about 20 km
inland from Ballina, sent me a message which indicated that 385 mm
of rain fell in 24 hours at Lowana with another location nearby
measuring over 400 mm. This information had been reported by an ABC
broadcast.
(6) Storm Energetics
--------------------
Mid-latitude (baroclinic) processes appeared to play a large role in
the genesis and intensification of the LOW. However, there also seemed
to be a significant contribution to the intensification before landfall
from oceanic and convective processes. The system as it approached the
coast was being steered by a deep layered ridge to the south while
under diffluent upper-level winds. This placed it in a low vertical
shear zone as it began moving over waters with the SST nearing 26 C.
The eye of the storm as it approached the coast was ragged with less
enhanced convection surrounding it than in the major rainband, which
was located southwest of the eye. The main destructive wind zone was
under this major rainband which was well-removed from the eye, and
therefore quite different from a tropical cyclone. This rainband
formed in a zone located between the LOW and a strengthening surface
ridge which moved northward up the New South Wales coast as the LOW
approached the coastline to the north.
C. Damage and Casualties
------------------------
The most extensive wind damage occurred along the coastal regions
between Evans Head and Brooms Head under separate rainbands some
distance from the eye of the storm. There was much less damage near
the point where the eye made landfall between Byron Bay and Ballina.
However, another area of significant wind damage occurred on the
Alstonville Plateau west of Ballina. This area rises abruptly out of
the coastal plains to the south and forms the foothills region of the
mountainous country to the north.
Extensive tree damage was reported in the Bundjalung National Park,
which extends from just south of Evans Head southward almost to Iluka.
In the Vineyard Haven area many trees with diameters between 0.5 and
0.75 metres were uprooted. The most extensive structural damage was
reported from the town of Yamba where around 100 buildings were
damaged. The whole Alstonville Plateau area and Lismore suffered
damage with large trees down or snapped off, power lines down, large
branches snapped off and leaf litter everywhere. Finally, in the
Tweed District a few houses experienced some roof damage.
In addition to wind damage, the torrential downpours the day after
the LOW had made landfall were responsible for some destructive flash
floods in the Brisbane and Logan City area. Damage from the flooding
has been estimated at $35 million. Matthew Saxby of Queanbeyan, New
South Wales, sent me a message citing an ABC report that damage from
recent flooding in New South Wales was expected to run into hundreds
of millions of dollars. There were floods in the area during the
previous month, so this figure may not refer only to damage caused by
the March subtropical LOW.
Matthew also sent along a report of the only fatality I've seen
mentioned in connection with the subject storm--a 12-year old boy
drowned after being washed out of his mother's car near Lawnton in
the northern outskirts of Brisbane.
***********************************************************************
SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E
Activity for March: 1 tropical cyclone of gale/storm intensity **
1 tropical cyclone of hurricane intensity **
** - both systems formed in February
South Pacific Tropical Activity for March
-----------------------------------------
As the month of March opened, two holdovers from February were
still on the charts. Intense Tropical Cyclone Paula had passed over
Vanuatu on 28 February, and on March 1st and 2nd passed to the south
of Fiji where strong winds and damaging seas were experienced. Much
farther east, weaker Tropical Cyclone Rita was moving southward during
the early days of the month well to the south of French Polynesia.
Complete reports on Paula and Rita can be found in the February
summary.
During the first few days of the month, two tropical disturbances
(11F and 12F) were mentioned by Nadi in the daily Tropical Disturbance
Summaries (TDS). Both were located east of the Dateline over the
waters between Tonga and French Polynesia. Neither developed into a
tropical cyclone, but the TDS for 2100 UTC on 3 March referred to 12F
as a tropical depression. The system was then located about 200 nm
southeast of Rarotonga and moving southeastward at 10 kts. No further
mention was made of this system in subsequent summaries. Also,
the TDS for 10 March referred to a system designated as Tropical
Depression 13F, located about 50 nm southwest of Rarotonga and moving
southeastward at 10 kts. This was the only referece to this system
available to the author. No tracks were included for these systems
in the cyclone tracks file for March. (Note: The tropical depression
in early April which developed into Tropical Cyclone Sose was also
numbered as 13F.)
***********************************************************************
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.
***********************************************************************
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: mar01.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: mar01.sum, for
example.
Back issues can also be obtained from the following websites
(courtesy of Michael Bath, Michael V. Padua, Tom Berg, Michael
Pitt, and Rich Henning):
http://australiasevereweather.com/cyclones/>
http://www.typhoon2000.com> OR http://www.geocities.com/taifun00/>
http://www.hurricanealley.net/>
http://www.qisfl.net/home/hurricanemike>
http://www.met.fsu.edu/gsc/Docs/Grads/henning/cyclones/>
Another website where much information about tropical cyclones may
be found is the website for the UK Meteorological Office. Their site
contains a lot of statistical information about tropical cyclones
globally on a monthly basis. The URL is:
http://www.met-office.gov.uk/sec2/sec2cyclone/sec2cyclone.html>
TROPICAL CYCLONE REPORTS AVAILABLE
JTWC now has available on its website the complete Annual Tropical
Cyclone Report (ATCR) for 2000 (1999-2000 season for the Southern
Hemisphere). Also, 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 2000 Atlantic and Eastern North Pacific
tropical cyclones; also, preliminary storm reports for all the 2000
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>
Prepared by: Gary Padgett
E-mail: [email protected]
Phone: 334-222-5327 (nights & weekends) / 850-882-2594 (weekdays)
***********************************************************************
***********************************************************************
|
Document: summ0103.htm
Updated: 29th December 2006 |
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