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Monthly Global Tropical Cyclone Summary July 1998
[Summaries and Track Data] [Prepared by Gary Padgett]
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Monthly Global Tropical Cyclone Summary July 1998 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
JULY, 1998
(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.)
***********************************************************************
JULY HIGHLIGHTS
--> Northwest Pacific season finally gets underway, but barely
--> First Atlantic tropical storm of the year develops
--> Northeast Pacific basin activity continues
***********************************************************************
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 have included a Glossary
of Abbreviations and Acronyms following the Author's Note at the end
of the summary.
***********************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for July: 1 tropical storm
NOTE: Much of the information presented below was obtained from the
TPC/NHC discussion bulletins issued with every regular advisory. All
references to sustained winds imply a 1-min averaging period unless
otherwise noted.
Tropical Storm Alex (TC #1)
27 July - 2 August
----------------------------
The season's first tropical storm (and depression) in the Atlantic
basin developed from a strong tropical wave which left the African
coast on 25 July. By late on the 26th the well-organized wave was
south of the Cape Verde Islands moving west at about 13 kts. The first
tropical depression advisory was issued by TPC/NHC at 1200 UTC on 27
Jul when the system was located about 250 nm south-southwest of the
Cape Verdes. Ship reports, satellite imagery, and scatterometer winds
all indicated a well-defined surface circulation. Initially the
depression was still involved with the monsoonal flow and did not
intensify very rapidly. Increasing convective organization was seen
on 28 Jul and the system was upgraded to Tropical Storm Alex at 0000
UTC on 29 Jul.
Alex intensified very slowly as it moved westward at a fairly good
clip. At 29/1800 UTC a Naval Oceanographic Office drifting buoy
located about 100 nm west-northwest of the center reported a 6-min avg
wind of 31 kts and a pressure of 1013 mb. Alex appeared better
organized on 30 Jul and winds were increased to 45 kts. Satellite
imagery revealed a central area of intense convection with fairly
symmetric outflow, although there was some south-southwesterly shear
over the system.
The storm's forward motion slowed somewhat on 31 Jul as the system
began to encounter increasing shear. Convection would intermittently
cover the center, but most of the time the center was exposed. Winds
were decreased to minimal tropical storm strength of 35 kts at 1800
UTC on 31 Jul but were bumped back up to 45 kts twenty-four hours later
after a reconnaissance flight on 1 Aug estimated surface winds of 45
kts with a central pressure of 1010 mb and ship FNPH reported gusts to
near hurricane force north of the center.
As Alex weakened it turned a bit more to the west-northwest. A
reconnaissance flight early on 2 Aug found only 24-kt winds near the
center but measured winds of 37 kts in a band 120 nm northeast of the
storm's center. However, a later flight could not locate a definite
surface circulation center so Alex was downgraded to a tropical
disturbance at 2100 UTC on 2 Aug about 400 nm east-northeast of San
Juan, Puerto Rico. The remnants of Alex persisted for a few days but
never showed any significant signs of re-developing. Since Alex
remained far from any populated areas, no deaths or damages are known
to have resulted from this tropical cyclone.
Tropical Storm Alex got the Atlantic tropical cyclone season off to
a later start than average, but not unusally so. The last year in
which the first named storm formed later than Alex was 1992, and that
storm was the very destructive Hurricane Andrew. (Coincidentally, Alex
is the replacement name for Andrew in the 6-year rotating list of
Atlantic tropical cyclone names.) In each of the seasons from
1993-1997 the first named storm has made its appearance on or before
1 July.
***********************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for July: 1 tropical storm
2 hurricanes
NOTE: Much of the information presented below was obtained from the
TPC/NHC discussion bulletins issued with every regular advisory (CPHC
for locations west of 140W.) All references to sustained winds imply
a 1-min averaging period unless otherwise noted.
Tropical Storm Celia (TC-04E)
17 - 21 July
------------------------------
The Northeast Pacific's third tropical storm of the season developed
from a large area of disturbed weather which passed just offshore of
the southwestern Mexican coast on 16 July. This disturbance produced
some locally heavy rains over adjacent coastal areas, but the author
has not learned of any casualties or significant damage due to any
flooding induced by the heavy rains. Early on 17 Jul the system began
to develop rather rapidly. The first advisory issued by TPC/NHC at 1500
UTC directly upgraded the disturbance to Tropical Storm Celia based on
a 45-kt wind report from ship KGTI. The low-level center was easily
observed by the radar at Cuyutlan, Mexico. Celia at this time was
located about 150 nm west-southwest of Manzanillo.
MSW in Celia were further increased to 50 kts at 0300 UTC on 18 Jul
based on a 17/1700 UTC report of 50-kt winds from ship 4XGX which was
located about 90 nm northeast of the center. The discussion mentioned
that Dvorak estimates were only 35 kts. Celia at this time was not
very well-organized. The storm initially moved on a northwesterly
trajectory but began to curve to a more west-northwesterly course as
it passed south of the tip of Baja California.
The center of the storm was observed by the Los Cabos radar as Celia
passed about 120 nm south of Cabo San Lucas shortly after 0600 UTC on
18 Jul at its peak intensity of 50 kts and estimated central pressure
of 1000 mb. The center of the circulation was embedded in a small
but concentrated area of deep convection. Based on a cumulative wind
distribution graphic on TPC/NHC's website, it is likely that gale-force
winds occurred just offshore from the tip of the Baja peninsula.
After passing south of Baja California Celia began to slowly weaken
as it continued on a westerly track out into the Pacific. Cooler SSTs
took their toll on the storm, although the weakening was slow to occur
since the circulation had become quite well-organized. The storm was
downgraded to a dissipating depression at 20/0600 UTC, and the final
advisory was issued at 0000 UTC on 21 Jul with the center located about
600 nm west of Cabo San Lucas.
Hurricane Darby (TC-05E)
23 July - 1 August
-------------------------
The first advisory on a newly developing tropical cyclone was issued
by TPC/NHC at 0600 UTC on 23 Jul with the depression centered about
625 nm south-southwest of Cabo San Lucas. Tropical Storm Darby was
christened 12 hrs later with 40-kt winds. Throughout its life Darby
moved on a fairly smooth west-northwesterly course which ultimately
took it well to the north of the Hawaiian Islands. Hints of an eye
began to appear early on 24 Jul and by afternoon a well-defined eye
was noted in satellite imagery. Darby was upgraded to a hurricane
at 24/1200 UTC when located about 650 nm southwest of Cabo San Lucas.
Hurricane Darby intensified quite rapidly, reaching an estimated
peak intensity of 105 kts by 25/0600 UTC. Minimum pressure was
estimated to have been 960 mb. The hurricane weakened slightly early
on 26 Jul, but by mid-day a large eye had reappeared. Darby had
apparently been undergoing a concentric eyewall replacement cycle.
As Darby continued moving farther to the west, its track paralleled
the 25 deg C isotherm so the storm did not weaken as quickly as
forecast--MSW remained at 100 kts through 28/0000 UTC.
The hurricane crossed 140W and entered the Honolulu AOR around
0600 UTC on 29 Jul. Darby was a minimal hurricane by this time and
was downgraded to a tropical storm on the next advisory from CPHC.
The combination of cooler SSTs and increased vertical shear caused
Darby to steadily weaken as it continued on its west-northwesterly
track which carried it well to the north of Hawaii. The system was
downgraded to a depression at 0600 UTC on 31 July about 350 nm north-
east of Hilo, and the final advisory was issued at 0000 UTC on 1 Aug
with the weak center about 250 nm north-northeast of Hilo. A weak
residual LOW was followed for a couple of days to near 26N, 166W at
0600 UTC on 3 Aug but showed no signs of re-intensification.
Hurricane Estelle (TC-06E)
29 July --->
---------------------------
Hurricane Estelle formed several hundred miles to the east of where
Darby had developed, but followed a similar general west-northwesterly
course out into the Central Pacific. The first advisory on Tropical
Depression 06E was issued at 1800 UTC on 29 Jul with the system
centered about 150 nm south-southwest of Acapulco. Tropical storm
intensity was attained 12 hrs later about 275 nm south-southeast of
Manzanillo, and Estelle was upgraded to a hurricane at 31/0600 UTC
when the storm was located about 500 nm south of Mazatlan, Mexico.
The TPC/NHC discussion at 0300 UTC noted that Estelle had a large
circulation that featured a strong core of central convection with
several rainbands containing convection of moderate intensity. The
bulletin accompanying the 1500 UTC advisory mentioned that convective
tops in the storm's central region were reaching -80 deg C.
By 0000 UTC on 1 Aug Hurricane Estelle was passing about 450 nm
south of Cabo San Lucas with MSW estimated at 75 kts. Although as of
this writing Estelle has dissipated in the Central Pacific, since the
storm reached its peak intensity after 1 Aug, further details of
Estelle's history will be contained in the August summary.
***********************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for July: 2 tropical depressions
1 tropical storm
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
'98 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.
Tropical Depression Akang (TC-01W)
7 - 11 July
-----------------------------------
The first tropical depression of 1998 was first identified by JTWC
at 1200 UTC on 7 Jul about 400 nm east-southeast of Okinawa. The
system moved erratically for a couple of days, and then followed a
fairly smooth west-northwesterly trajectory which took it through the
extreme southernmost Ryukyu Islands and into northern Taiwan. On
8 Jul PAGASA initiated bulletins on the depression and named it Akang.
Tropical Depression Akang battled vertical wind shear throughout its
life and never became very well-organized. By 09/0000 UTC most of
the central convection had been sheared toward the southwest, leaving
a completely exposed low-level center. The shear continued, causing
the low-level circulation to become elongated.
Akang limped ashore onto the northern tip of Taiwan near Taipei,
and was dissipating by 0000 UTC on 11 Jul. MSW were estimated at
30 kts with an estimated minimum pressure of 1002 mb (from JMA's
advisories).
Tropical Storm Nichole (TC-02W / TS 9801)
8 - 12 July
------------------------------------------
The Northwest Pacific basin's first tropical storm of 1998 was named
on 8 July, making this year the latest-beginning tropical storm
season in that basin at least since 1959. (This bit of information
came from Mark Lander of the University of Guam.) A tropical
depression had formed in the northern South China Sea between China
and northern Luzon by 08/0000 UTC. The first JTWC advisory placed the
center about 250 nm east-southeast of Hong Kong. TD-02W drifted
northward, becoming Tropical Storm Nichole at 1800 UTC. A small CDO
had developed and outflow had increased on the southern side of the
depression.
Over the next couple of days Nichole appeared to describe a small
clockwise loop just west of the southern tip of Taiwan. The JTWC
advisory issued at 10/0300 UTC stated that local station information
indicated a landfall on Taiwan had been made near 09/1740 UTC and
that synoptic observations supported minimal tropical storm intensity
at the time. Peak intensity of 45 kts (with an estimated minimum
pressure of 998 mb) was reached about that time. Nichole was down-
graded to a depression at 0600 UTC on 10 Jul as it drifted westward
in the Taiwan Straits.
During this time the system remained poorly organized with an
exposed low-level center and limited convection sheared to the south
side of the center. After 12/0600 UTC the weak depression turned
northward and was dissipating inland over China by 1800 UTC.
Tropical Depression (TC-03W)
24 - 27 July
-----------------------------
This tropical depression was associated with what seems to have
been a rather complex weather system east of Japan in late July. In
fact, it might be more appropriate to say "depressions" since the
circulation carried in JMA High Seas Forecasts on 24 and 25 July
appears to have been a distinct center from that identified by JTWC as
TD-03W beginning at 25/0000 UTC. The Significant Tropical Weather
Advisory (STWA) issued at 25/0100 UTC mentioned a large gyre-like upper
LOW off the east coast of Japan with numerous vorticity maxima in its
periphery. Special attention was called to two distinct centers.
One was a low-level circulation near 28N, 142E (about 200 nm north-
northeast of Iwo Jima), and this appears to be the center that had been
carried by JMA for about 24 hrs. The first JMA bulletin on that
depression was issued at 0000 UTC on 24 Jul and placed the center about
300 nm east of Iwo Jima. It had moved generally in a northwesterly
direction to the aforementioned coordinates. Maximum winds reported
by JMA were 30 kts (10-min avg). The STWA mentioned that an area of
deep convection might be wrapping around the periphery of the broad
cyclonic circulation but that the convection was located over 80 nm
from the exposed center. MSW was estimated to be only 15-20 kts with
a central pressure of 1004 mb.
The same STWA mentioned another area of convection near 26N, 149E
which was associated with a rapidly developing circulation that was
tracking toward the north. It was apparently this center that JTWC
classified as TD-03W. The depression was located about 425 nm east-
northeast of Iwo Jima at 25/0000 UTC and was moving north-northwestward
at a fairly quick pace. The center that had been tracked by Japan
on 24 Jul was followed to near 29N, 141E by 25/1200 UTC but was
subsequently dropped from the High Seas Forecasts.
TD-03W tracked northward east of Japan, passing about 250 nm east
of Tokyo around 0300 on the 26th. By 1800 UTC on 25 Jul the low-level
center had become exposed about 35 nm from the nearest convection.
By 26/0000 UTC there was no deep convection remaining near the center.
On 26 Jul the weakening depression turned to the north-northeast and
accelerated away from Japan. The system had initially been forecast to
reach tropical storm intensity, but the vertical shear it encountered
thwarted any further strengthening.
***********************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for July: No tropical cyclones
Additional Information on Arabian Sea Cyclone
(TC-03A) 4 - 9 June
---------------------------------------------
The author has uncovered a little more information on the effects
of the deadly Arabian Sea cyclone (TC-03A) which devastated the coast
of northwestern India in early June. The source for this was the
website of the UN Office for the Coordination of Humanitarian Affairs
(OCHA) - . According to this report (dated
19 Jun 1998), 1126 bodies had been recovered but the death toll could
be as high as 3000 in the Kutch-Saurashtra region of Gujurat. About
1745 persons were still missing and 893 were reported injured. The
number of houses/huts damaged was put at 158,000 and financial loss
was estimated at Rs. 120 billion (about 3.01 billion U.S. dollars).
In addition, in Rajasthan District, 11 persons died and 14,603 houses/
huts were damaged.
***********************************************************************
SOUTH INDIAN OCEAN (SIO) - South Indian Ocean West of Longitude 90E
Activity for July: 1 tropical depression
NOTE: The information presented below was gleaned from releases by
the La Reunion TCWC, which is the WMO's Regional Specialized Meteor-
ological Centre (RSMC) for the South Indian Ocean; and also from
warnings issued by JTWC. References to sustained winds imply a
10-min averaging period unless otherwise stated. A special thanks
to Alain Soulan and Paul Remois for passing along some information
on nomenclature and warning practice in this basin.
Tropical Depression "H4" (TC-01S)
20 - 25 July
----------------------------------
First, a few comments about cyclone nomenclature and classification
in the South Indian basin:
(1) La Reunion utilizes a more rigid and restrictive definition of the
term "tropical depression" than do most TCWC's. To be classed as
a tropical depression a disturbance must be adjudged to have a
10-min MSW of at least 28 kts (i.e., Beaufort force 7). Weaker
systems for which advisories are issued are called "tropical
disturbances".
(2) In the South Indian basin the term "tropical cyclone" is reserved
for systems which reach a 10-min MSW of 64 kts--hurricane force.
Depressions are named when 10-min MSW exceed 34 kts and are
called "tropical storms", as in U.S. and Japanese usage. When
MSW exceed 47 kts (storm force) the system is called a "severe
tropical storm".
(3) Whenever a tropical disturbance has become sufficiently organized
to warrant advisories being issued, the disturbance is given a
two-character designator. The first character is the initial
letter of the next cyclone name on the annual list (in this case,
Hillary). The second character is a digit which is a sequential
count of significant disturbances occurring since the last storm
was named. Thus, "H4" was the fourth disturbance occurring
since Tropical Storm Gemma was named in April, but was the first
of these to reach tropical depression intensity.
(4) In the South Indian basin the tropical cyclone season is
considered to run from 1 Aug to 31 Jul instead of from 1 Jul to 30
Jun, as is the case with Australia and Fiji. But JTWC's numbering
scheme for Southern Hemisphere tropical depressions and cyclones
starts anew on 1 Jul each year; hence, this depression was
considered by JTWC to be the first of the 1998/99 season while
La Reunion will regard it as the last one of the 1997/98 season.
The first advisory by La Reunion was issued at 0600 UTC on 20 Jul
with the disturbance centered about 800 nm east of Diego Garcia. The
system moved rather slowly toward the west-southwest for a couple of
days. It was upgraded to a tropical depression with 30-kt MSW at
0600 UTC on 22 Jul. The center was estimated to be about 400 nm
east-southeast of Diego Garcia at this time. By 23/0000 UTC the
system was showing signs of weakening and was downgraded to a tropical
disturbance. Interestingly, it wasn't until 0600 UTC on the 23rd
that JTWC issued its first advisory, placing the depression center
about 300 nm southeast of Diego Garcia.
La Reunion dropped the system 6 hrs later, but JTWC continued
issuing advisories until 25/0000 UTC. During this period the
center stalled and began to drift northward and then to the east-
northeast. The final advisory located the center about 300 nm east-
southeast of Diego Garcia.
This depression experienced considerable vertical shear throughout
its life. At 1800 UTC on 21 Jul the system exhibited an exposed
center with the nearest organized convection about 60 nm distant.
By early on the 23rd the shear had abated somewhat and the low-level
circulation appeared to be better organized. Given the proximity
to Diego Garcia and the slight possibility that the system might
reach tropical storm strength, JTWC decided to initiate advisories.
***********************************************************************
AUSTRALIAN REGION (AUG) - From Longitude 90E Eastward to Longitude 160E
Activity for July: No tropical cyclones
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SOUTHWEST PACIFIC (SWP) - South Pacific Ocean East of Longitude 160E
Activity for July: No tropical cyclones
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AUTHOR'S NOTE: This summary should be considered a very preliminary
overview of the tropical cyclones that occur in each month. The cyclone
tracks (provided separately) will generally be based upon operational
warnings issued by the various tropical cyclone warning centers. The
information contained therein may differ somewhat from the tracking and
intensity information obtained from a "best-track" file which is based
on a detailed post-seasonal analysis of all available data. Information
on where to find official "best-track" files from the various warning
centers will be passed along from time to time.
The track files are not being sent via e-mail. They can be retrieved
in the following manner:
(a) FTP to: hrd-type42.nhc.noaa.gov [140.90.176.206]
(b) Login as: anonymous
(c) For a password use your e-mail address
(d) The files will be named with an obvious nomenclature--using
July as an example: jul98.tracks
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 July summary is the tenth cyclone summary in this series;
the first one covering the month of October, 1997. If anyone did
not receive any of the previous summaries, they may be downloaded
from the aforementioned FTP site at HRD. The summary files are
catalogued with the nomenclature: oct97.sum, for example.
Back issues can also be obtained from the following websites
(courtesy of Michael Bath and Michael V. Padua):
http://australiansevereweather.com/cyclones/>
http://www.geocities.com/capecanaveral/6825> (since January only)
The preliminary storm reports for all the 1997 Atlantic and Eastern
North Pacific tropical cyclones are available on the Tropical
Prediction Center's website: http://www.nhc.noaa.gov> . These
reports include the analyzed best-track for each cyclone. The staff
of JTWC is also working on an on-line version of their Annual Tropical
Cyclone Report for 1997. It is still under construction, but the
best-track files are already available for 1997 Northwestern Pacific
and North Indian Ocean cyclones. The URL is:
http://www.npmocw.navy.mil/npmocw/prods/jtwc.html>
Prepared by: Gary Padgett
E-mail: [email protected]
Phone: 334-222-5327
***********************************************************************
GLOSSARY of ABBREVIATIONS and ACRONYMS
AOML/HRD - Atlantic Oceanographic and Meteorological Laboratory/
Hurricane Research Division, located on Virginia Key, Miami,
Florida, U.S.A.
AOR - area of responsibility
CDO - central dense overcast
CPHC - Central Pacific Hurricane Center, Honolulu, Hawaii, U.S.A.
FLW - flight level winds
FTP - file transfer protocol
IMD - India Meteorological Department (RSMC New Delhi, India)
JMA - Japanese Meteorological Agency (RSMC Tokyo, Japan)
JTWC - Joint Typhoon Warning Center, Guam
kt - knot = 1 nautical mile per hour
m - meter, or metre
mb - millibar, numerically equivalent to hectopascal
mm - millimeter
MSW - maximum sustained wind(s) (either 1-min avg or 10-min avg)
nm - nautical mile = 6076.12 feet or 1852.0 meters
NPMOC - Naval Pacific Meteorological and Oceanographic Center, Pearl
Harbor, Hawaii, U.S.A.
PAGASA - Philippines' Atmospheric, Geophysical & Astronomical Services
Administration
RSMC - Regional Specialized Meteorological Centre
SST - sea surface temperature
STS - severe tropical storm (MSW greater than 47 kts)
TC - tropical cyclone
TCWC - Tropical Cyclone Warning Centre (generic term)
TD - tropical depression
TPC/NHC - Tropical Prediction Center/National Hurricane Center, Miami,
Florida, U.S.A.
TS - tropical storm
WMO - World Meteorological Organization, headquartered at Geneva,
Switzerland
UTC - Universal Time Coordinated, equivalent to Greenwich Mean Time
or Zulu (Z)
***********************************************************************
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Document: summ9807.htm
Updated: 18th March 2008 |
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