[Index]
Monthly Global Tropical Cyclone Summary August 1998
[Summaries and Track Data] [Prepared by Gary Padgett]
| Tropical
Cyclones
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Monthly Global Tropical Cyclone Summary August 1998 [Summaries and Track Data] [Prepared by Gary Padgett] |
MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
AUGUST, 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.)
***********************************************************************
AUGUST HIGHLIGHTS
--> United States struck by hurricane and tropical storm
--> Eastern Pacific continues active
--> First two Western Pacific typhoons of year develop
***********************************************************************
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 last month's 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 it last month and wishes to receive a copy, send me an
e-mail privately and I'll forward them a copy.
***********************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for August: 3 tropical storms
2 hurricanes
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. Also, a special thanks to Eric Blake, a graduate
student at Colorado State University and owner of the Atlantic Tropical
Weather Center website, for passing along some buoy and ship reports
from Hurricane Bonnie.
Tropical Storm Alex (TC #1)
27 July - 2 August
----------------------------
As the month of August opened, the Atlantic's first tropical storm
of the season was battling rather strong vertical shear east of the
Leeward Islands. Although Alex was near its peak intensity of 45 kts
on 1 Aug, the system began to weaken rapidly and dissipated on 2 Aug
to the northeast of the Leewards. The history of Tropical Storm Alex
was covered in its entirety in the July summary and its complete track
given in the accompanying tracking file for July.
Hurricane Bonnie (TC #2)
19 - 30 August
-------------------------
A tropical wave left the west African coast during the second week
of August and moved slowly across the Atlantic. A large, broad
circulation resembling a monsoon gyre accompanied the wave for several
days. By 19 Aug the cloud pattern had become more consolidated over
the northwest portion of the system so TPC/NHC issued the first
depression advisory on the system at 2100 UTC, locating its broad
center about 925 nm east-southeast of San Juan, Puerto Rico. The
depression continued moving to the west-northwest at a pretty good
clip, and the first reconnaissance flight into the system on 20 Aug
found flight-level winds to 61 kts north of the center; therefore, the
depression was upgraded to Tropical Storm Bonnie at 2100 UTC about
375 nm east of San Juan.
Bonnie initially moved rather rapidly west-northwestward, passing
about 100 nm north of San Juan around 1800 UTC on 21 Aug. The storm
steadily increased in intensity with winds reaching hurricane force
around 22/0600 UTC. Bonnie was centered at that time about 250 nm
northwest of San Juan. The hurricane's forward motion slowed
considerably on 22 and 23 Aug, and the track became more of a north-
westerly one. Late on 22 Aug an Air Force Reserves reconnaissance
flight measured a central pressure of 962 mb, which represented a drop
of 15 mb in 8 hours. By 1200 UTC on 23 Aug Bonnie's pressure had
dropped to 957 mb and the MSW had increased to 100 kts, making Bonnie
a Category 3 hurricane on the Saffir/Simpson scale. The storm was
centered at that point about 500 nm east-southeast of Miami. The
lowest pressure in Bonnie's history came on the evening of 23 Aug when
a reconnaissance flight measured a central pressure of 954 mb. Bonnie
was a large hurricane by Atlantic standards. From the time the storm
reached its peak intensity until landfall, gale-force winds covered
an area over 300 nm in diameter, and hurricane-force winds eventually
covered an area nearly 150 nm in diameter before the hurricane made
landfall.
Hurricane Bonnie continued on a steady northwesterly course toward
the U.S. East Coast, gradually becoming more northerly early on 26 Aug.
The eye of Hurricane Bonnie reached the Cape Fear, North Carolina, area
late in the afternoon of 26 Aug and then turned to more of a general
northeasterly course which allowed the center to "slide" along the
coast, gradually moving inland. The hurricane's forward motion also
slowed after making landfall, creating the potential for some very
serious flooding from heavy rainfall. Bonnie's center gradually
acquired a more east-northeasterly component of motion which allowed
it to more or less skirt the coastal plain. The storm exited the
state near Nag's Head on the Outer Banks around 28/0000 UTC--a little
more than 24 hours after first touching the Cape Fear area.
During the three days preceeding the hurricane's landfall the
central pressure, as measured by reconnaissance flights, fluctuated
generally between 960 and 965 mb. A slight weakening of Bonnie may
have been caused by the slow, quasi-stationary movement on 23 and 24
Aug which would have allowed SST cooling due to upwelling. As the
hurricane approached the coast, it appeared also to entrain some drier
air which led to a somewhat ragged appearance in satellite imagery.
However, through all this, reconnaissance flights continued to find
flight-level winds between 100 and 120 kts. Dvorak intensity
estimates during this time were significantly lower than those
provided by aircraft, thus underscoring the great value of aerial
reconnaissance, especially in hurricanes that are threatening populated
areas.
On 25 Aug at 1800 UTC ship ZCBK6, located about 70 nm southeast of
Bonnie's center, reported a sustained wind of 70 kts from 200 degrees;
while at the same time, ship C6T20, located roughly 80 nm south-
southwest of the center, reported sustained 60-kt winds from 300
degrees. Both ships recorded a pressure near 991 mb.
Around 1700 UTC on 26 Aug a NOAA research aircraft reported winds
of 116 kts at the 2450 m flight level in the northeast quadrant of
the hurricane. Also, a GPS dropwindsonde released during the afternoon
by an Air Force reconnaissance plane measured 110 kts in the eastern
eyewall not far above the surface. The automatic reporting station
at Frying Pan Shoals (33.5N, 77.5W) reported sustained winds of
hurricane force during Bonnie's passage. At 26/2100 UTC the center
of Bonnie was about 30 nm northwest of the station, and the reported
sustained wind was 65 kts (150 degrees). Pressure was 972.7 mb and
the peak gust during the preceeding hour was recorded at 90 kts.
By 0000 UTC on 27 Aug the center of Hurricane Bonnie was located
about 40 nm north-northwest of Frying Pan. The sustained wind at
this time was being reported at 70 kts (170 degrees), with a peak
gust over the past hour of 83 kts and a pressure of 982.7 mb. (It
should be noted that the elevation of the anemometer at Frying Pan
Shoals is 44.2 m above MSL. Thanks to Eric Blake for passing this
piece of information along.)
While overland Bonnie was downgraded to a 55-kt tropical storm, but
winds began to increase as the center approached the coast. During
the evening of the 27th a reconnaissance flight measured winds of 82
kts at 3050 m, so Bonnie was once more upgraded to a hurricane at
28/0300 UTC. The storm was at this time located near Nag's Head or
about 50 nm north-northwest of Cape Hatteras. At 27/2200 UTC Diamond
Shoals Lighthouse (anemometer elevation 46.6 m) reported a sustained
wind of 63 kts (190 degrees) with a peak gust over the preceeding hour
of 76 kts. Chesapeake Lighthouse reported sustained winds of 68 kts
and Cape Henry reported 70 kts, but the heights of these anemometers
and the time of the reports are unknown to the author.
Flight-level winds on the morning of 28 Aug were reported at 90
kts, but surface winds were estimated at only 55 kts. Bonnie was
kept at hurricane intensity through the 1500 UTC advisory, but
downgraded to a tropical storm at 2100 UTC when centered about 200 nm
south of New York City. Apparently a strong southerly flow from over
the Gulf Stream advected latent and sensible heat into the cyclone and
allowed it to maintain its strength for awhile longer even though it
was moving over cooler SSTs. Bonnie accelerated to the northeast,
passing well to the south of the Canadian Maritimes.
MSW had decreased to 45 kts by 29/2100 UTC, but were upped back to
50 kts based on observations from Canadian buoy 44137, Sable Island
and a ship report. The center of Bonnie passed just south of Sable
Island at 0200 UTC on 30 Aug. An oil rig just east of the island
reported a 65-kt wind from an anemometer located 100 m above sea
level. Bonnie had become sufficiently extratropical that TPC/NHC
issued the last advisory on the morning of the 30th, placing the
center of the storm about 150 nm south of Cape Race, Newfoundland,
at 1200 UTC.
Damage from Hurricane Bonnie was widespread, but not as major as
had been anticipated. There were reports of downed power lines,
uprooted trees, broken limbs, roof damage, and damage to crops
(especially the tobacco crop); but the magnitude of the losses was
not nearly as great as with Hurricane Fran in 1996. There doesn't
seem to have been a whole lot of storm surge flooding damage along
the beachfront. Bonnie dropped up to 254 mm of rain on eastern
North Carolina which resulted in some flooding, but not to the degree
which had been feared. The Governor of North Carolina, as quoted
in the press, stated that losses would likely run between $1 and $2
billion--much of this being agricultural losses. The author was
able to locate an account of two deaths attributed to Hurricane Bonnie.
About 1 million persons in North Carolina and 300,000 in Virginia
lost electrical power during the storm.
I know this account of Hurricane Bonnie is exceptionally long, but
I wanted to mention one other interesting feature. The first space-
borne rain radar, located onboard the Tropical Rain Measuring Mission
(TRMM) spacecraft (a joint U.S.-Japanese venture), produced images
of a tall chimney cloud in the eyewall of Bonnie on 22 Aug which
reached about 59,000 ft (almost 18,000 m) into the atmosphere.
According to Dr. Robert Simpson, a former director of TPC/NHC, such
tall clouds are rarely seen in Atlantic hurricanes.
Tropical Storm Charley (TC #3)
21 - 22 August
-------------------------------
The origin of Tropical Storm Charley can be traced back to an
area of disturbed weather that was tracked from the southeastern Gulf
of Mexico into the central Gulf. By the afternoon of 20 Aug cloudiness
and showers were becoming better organized. On the morning of 21 Aug
an Air Force Reserves reconnaissance plane closed off a weak low-level
center about 250 nm southeast of Corpus Christi, Texas. TPC/NHC
issued the first depression advisory at 1500 UTC. The depression
moved northwestward toward the Texas coast during the afternoon, and
was upgraded to Tropical Storm Charley at 2100 UTC after a plane
reported flight-level winds (450 m) of 42 kts northeast of the center
and some oil rigs reported winds to 37 kts in a small area north of the
center.
Charley's peak intensity of 50 kts and lowest pressure of 1003 mb
were reached around 22/0600 UTC while centered only about 20 nm off
the southern Texas coast. A reconnaissance aircraft reported a
maximum flight-level wind (1500 m) of 57 kts while wind estimates from
the Corpus Christi (KCRP) WSR-88D ran from 60-65 kts between 1050 and
1350 m elevation. The Rockport ASOS reported a sustained wind of 36
kts with a gust to 42 kts at 22/0800 UTC. Tropical Storm Charley made
landfall around daybreak near Port Aransas (near Corpus Christi) and
was downgraded to a depression at 1500 UTC.
While Charley's winds quickly abated, a serious flooding threat
began to develop from the heavy rains. The remnants of Charley moved
slowly westward over the next several days, causing very heavy rains
over portions of southern Texas. Almost 460 mm fell in the vicinity
of Del Rio, Texas--a city of 30,000 located about 150 miles (240 km)
west of San Antonio. Just about the entire city was inundated--water
reached a depth of 2.5 m in some streets. The latest account located
by the author mentioned 17 known fatalities with perhaps 50 more
unaccounted for in the Del Rio area and across the Rio Grande in
Ciudad Acuna, Mexico.
Hurricane Danielle (TC #4)
24 August - 5 September
---------------------------
A strong tropical wave which left the west coast of Africa around
20 Aug began to show signs of increased organization by 23 Aug when
located several hundred miles west-southwest of the Cape Verdes. The
system became much better organized on 24 Aug and was classified as a
tropical depression about 700 nm west of the Cape Verdes in a special
advisory issued at 1530 UTC. Tropical Storm Danielle with 35-kt
winds was christened six hours later. Danielle began as a very small,
compact tropical cyclone. By the morning of 25 Aug satellite pictures
showed a small pinhole eye so the storm was upgraded to a hurricane at
1500 UTC about 1100 nm west of the Cape Verdes.
Danielle reached an estimated peak intensity of 90 kts on 26 Aug
when its center was imbedded in some -70 deg C cloud tops, but weakened
some during succeeding days as some southerly shear disrupted its cloud
pattern. The first reconnaissance flight into the storm late on the
26th found flight-level winds of 77 kts over the northeast quadrant
but only 37 kts over the southwest quadrant. This very asymmetric
wind field was likely caused by a combination of the rapid forward
translational speed--18 kts--and the large pressure gradient
associated with a ridge to the north. The lowest central pressure
measured at the time was 992 mb. Very early on 27 Aug another flight
found 90-kt winds in the northeast quadrant in very deep convection
with tops between -70 and -75 deg C. The minimum pressure was only
993 mb--somewhat high for such strong winds--but a situation which has
been observed in compact hurricanes before.
Hurricane Danielle moved on a fairly straight west-northwestward
course from its point of origin to its point of recurvature on 31 Aug
about 325 nm east of Cape Canaveral, Florida, passing about 250 nm
north of Puerto Rico early on 28 Aug. The hurricane weakened along
the way, partly due to the aforementioned shear, and partly due
to moving over patches of water whose SSTs had been cooled several
degrees by Bonnie's recent passage through the same area. However,
after recurving to the northeast, Danielle began to undergo a modest
strengthening once more. The minimum pressure of 965 mb was measured
around 1800 UTC on 1 Sep when the hurricane was centered about 300 nm
west of Bermuda. Attendant MSW was estimated at 85 kts after a
reconnaissance flight found 94-kt winds at flight level.
The hurricane's closest approach to Bermuda came around 02/0600 UTC
when the center was about 175 nm northwest of the island. The area
of gale-force winds had expanded considerably, especially to the south-
east of the eye. An observation from Bermuda at 02/1100 UTC reported
sustained winds of 34 kts with a gust to 47 kts. After passing Bermuda
Danielle began to accelerate rapidly off to the northeast. The storm
passed about 400 nm south of Halifax, Nova Scotia, around 1800 UTC on
the 2nd.
A Canadian buoy (ID 44141 at 42.1N, 56.2W) recorded a 66-kt wind
and a pressure of 976 mb at 0700 UTC on 3 Sep. At 0900 UTC a pressure
of 962 mb, 54-kt winds, and 16 m seas were reported from the same buoy.
Around mid-day Danielle passed south of another Canadian buoy (ID 44138
near 44.3N, 53.7W) which reported winds of 45 kts, a pressure of 972
mb, and 12 m seas. On 3 Sep Danielle transformed into a very vigorous
extratropical cyclone with the last TPC/NHC advisory placing the center
about 150 nm southeast of Cape Race, Newfoundland. The deep extra-
tropical storm continued rapidly eastward across the North Atlantic,
passing well north of the Azores by early on 5 Sep.
Since Danielle continued as a tropical entity for only three days
into the month of September, I have chosen to report its entire history
in this summary issue. The accompanying tracking file contains the
complete track of Hurricane Danielle, including its extratropical stage
through 0600 UTC on 5 Sep. Except for its brush with Bermuda, Danielle
did not affect any populated areas. It is likely that any affects
experienced in Bermuda were very minimal.
Tropical Storm Earl (TC #5)
31 August --->
----------------------------
Tropical Storm Earl, which later became Hurricane Earl, developed
from a tropical wave which had moved off the coast of western Africa
around mid-August. This wave followed the wave which produced Bonnie
but preceeded the disturbance from which Danielle developed. The
system had gotten better organized by 22 Aug and had moved into the
eastern Caribbean by 23 Aug, but its development began to be hindered
by the outflow from Hurricane Bonnie, located to the northwest. The
wave weakened and continued slowly across the Caribbean during the
ensuing week.
By 31 Aug the main area of disturbed weather associated with the
wave had moved into the southwestern Gulf of Mexico. During the
afternoon a reconnaissance plane flew into the broad area of low
pressure in the southwestern Gulf. Even though the circulation was
broad and disorganized, the plane found a peak wind of 43 kts at 450 m
and a pressure of 1002 mb. The disturbance was upgraded directly to
Tropical Storm Earl at 31/2100 UTC.
Earl proved to be a very unusual tropical cyclone that was very
difficult to track. The saga of Earl will continue in next month's
summary. No track is given in the accompanying tracking document
for this month.
***********************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for August: 1 tropical depression
1 tropical storm
3 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.
Hurricane Estelle (TC-06E)
29 July - 8 August
---------------------------
Hurricane Estelle had developed on 29 Jul about 150 nm south-
southwest of Acapulco, Mexico, and had reached hurricane intensity
on 31 Jul about 500 nm south of Mazatlan. (A few more details of
Estelle's early history were covered in the July summary.) During
its life Hurricane Estelle followed a fairly straight general west-
northwesterly course from its point of origin south of Mexico to
its point of dissipation well to the northeast of Hawaii.
By 0000 UTC on 1 Aug Hurricane Estelle was passing about 450 nm
south of Cabo San Lucas with MSW estimated at 75 kts. Late that day
a well-defined eye surrounded by a ring of intense convection had
appeared. Estelle reached its peak intensity of 115 kts with an
attendant estimated central pressure of 948 mb at 0600 UTC on 2 Aug
when located about 550 nm southwest of Cabo San Lucas. By the
afternoon of 3 Aug the hurricane had weakened considerably as it
passed into a region of cooler SSTs (25-26 deg C). The hurricane
was downgraded to a 60-kt tropical storm at 04/0600 UTC, and was
downgraded to a depression 30 hrs later when located over 1300 nm
west of Cabo San Lucas.
Estelle had been a large and powerful hurricane, so it took several
days for the circulation to spin down. The weakening depression
was still close to tropical storm intensity when it crossed 140W into
the Honolulu area of warning responsibility around 1800 UTC on the 6th.
Further weakening ensued and the final advisory was written by the
CPHC at 1800 UTC on 8 Aug, locating the weak center about 400 nm north-
northeast of Hilo. The remnants were tracked westward for several more
days to near 23N, 170W (about 625 nm west of Lihue, Hawaii) at
15/0000 UTC.
Tropical Storm Frank (TC-07E)
6 - 10 August
------------------------------
A tropical disturbance several hundred miles south-southwest of Cabo
San Lucas showed increased signs of organization on 6 Aug, and at 1800
UTC the first depression advisory was written by TPC/NHC, placing the
poorly-defined center about 75 nm southwest of Socorro Island.
Observations from Socorro and a ship 150 nm south of the center helped
to confirm that a surface circulation existed, although it was
elongated along a north-northeast/south-southwest axis. Initially,
this system was not expected to intensify into a tropical storm.
The depression began tracking in a general northward direction.
At 07/1800 UTC Socorro Island, located then about 120 nm south-
southeast of the center, reported south winds at 25 kts, with 1008.7 mb
following a 3-hr pressure rise of 3.1 mb. Visible and infrared
satellite imagery showed better organization as the day progressed,
and the depression was upgraded to Tropical Storm Frank at 08/0300
UTC after the T-number from TABF had reached 2.5 and several ships
about 100 nm northeast of the center reported winds of 25 to 33 kts.
At 0000 UTC Frank's center was estimated to be about 150 nm southwest
of Cabo San Lucas.
Tropical Storm Frank remained a minimal tropical storm as it trekked
northward. The center passed about 140 nm west of Cabo San Lucas
around 1200 UTC on 8 Aug. It was initially believed that the center
of Frank made landfall on the Baja coast at 09/0600 UTC about 125 nm
southeast of Punta Eugenia, but later satellite fixes indicated the
center was about 100 nm to the west. The 09/1200 UTC analyzed
position was estimated to be about 50 nm south-southwest of Punta
Eugenia. At this time Frank consisted of a low- to mid-level
circulation without much deep convection. The weakening depression
turned more to the northwest (which was what most models had predicted
all along) and had dissipated by 0000 UTC on 10 Aug about 125 nm west-
northwest of Punta Eugenia.
The lowest central pressure in Frank was estimated to have been
1001 mb on 8 Aug about the time the center was due west of Cabo San
Lucas. Rainfall from the tropical storm affected portions of north-
western Mexico and the southwestern United States, but the author has
not learned of any significant damage or any casualties resulting
from these rains.
Hurricane Georgette (TC-08E)
11 - 17 August
-----------------------------
The first advisory on TD-08E was issued by TPC/NHC on 11 Aug at
0900 UTC, locating the center about 550 nm southwest of Manzanillo,
Mexico, at 0600 UTC. In contrast to several of this season's North-
eastern Pacific hurricanes, Georgette moved on more of a northwesterly
course throughout its life which carried it to a fairly high latitude
well west of the Baja California peninsula. The depression was
upgraded to Tropical Storm Georgette at 11/1800 UTC and to a hurricane
with 65-kt winds at 1200 UTC on 12 Aug when centered about 575 nm
west-southwest of Manzanillo.
Georgette continued moving northwestward and reached its estimated
peak intensity of 100 kts and 960 mb pressure at 14/0600 UTC. At this
point the hurricane was located about 570 nm west-southwest of Cabo
San Lucas. According to a TPC/NHC discussion, Georgette represented
an excellent example of a banding-type hurricane. At 0900 UTC on
13 Aug the discussion bulletin mentioned that the system had a small
CDO which, when combined with the principal convective band, appeared
in infrared imagery in the shape of the number "6". At the time of
its peak intensity, Georgette featured a large eye--around 35 nm in
diameter--which was surrounded by a ring of deep convection, but with
little deep convection elsewhere.
By early on 15 Aug Georgette was beginning to rapidly weaken as it
moved over 23 deg C SSTs. At 0600 UTC the storm, still with 85-kt
winds, passed about 725 nm west of Cabo San Lucas, moving northwest-
ward. Georgette was downgraded to a tropical storm at 16/0000 UTC
and to a depression 18 hrs later. The last advisory, at 0300 UTC
on the 17th, placed the dissipating center about 650 nm west-southwest
of Punta Eugenia on the west coast of the Baja.
Tropical Depression (TC-01C)
16 - 19 August
-----------------------------
The only tropical cyclone thus far this season to form in the area
of warning responsibility of the CPHC in Honolulu began to take shape
on 15 Aug. A disturbance about 800 nm east-southeast of Hilo, located
on a northward bulging ITCZ, began to get better organized, and TD-01C
had formed by 1200 UTC on 16 Aug. Ship reports of 30 kts and visible
satellite pictures confirmed that a closed circulation had developed.
Infrared pictures indicated that a convective band was trying to wrap
around the east side of the center. The depression, with 30 kts winds,
was initially forecast to reach tropical storm intensity, but this
never materialized. (Had this system become a tropical storm, its
name would have been Upana--a Hawaiian name.)
The tropical depression moved generally westward as vertical shear
inhibited development. Deep convection followed a diurnal pattern,
increasing to a maximum during the night and weakening during the
daytime hours. MSW were decreased to 25 kts by 17/1200 UTC, and
the last advisory was written at 0000 UTC on the 19th placing the weak
center about 325 nm south of Hilo.
Hurricane Howard (TC-09E)
21 - 29 August
--------------------------
On the afternoon of 20 Aug satellite pictures indicated that an
area of disturbed weather about 375 nm south of Acapulco had become
significantly better organized. The previously exposed low-level
center had become positioned under deep convection associated with
a primary banding feature to the east. A ship report of 40-kt winds
and a 1005 mb pressure from just north of the center at 21/0000 UTC
led to the system being upgraded directly to Tropical Storm Howard.
Howard moved generally on a west-northwestward course for most of
its life. The storm strengthened quite rapidly, reaching hurricane
intensity at 1800 UTC on 21 Aug about 350 nm south-southwest of
Acapulco. Hurricane Howard began to deepen explosively during the
morning of 22 Aug. MSW increased from an estimated 95 kts at 1200 UTC
to a peak of 130 kts only 12 hrs later. Minimum central pressure was
estimated at 930 mb with an eye diameter of 11 nm. Hurricane Howard
was the strongest hurricane seen in the Northeastern Pacific basin
thus far this season. After reaching its peak intensity Howard slowly
weakened, with estimated MSW dropping to 105 kts by 24/1800 UTC. At
this point the eye was quite large with an apparent double structure.
It is possible that there was a mesocyclone rotating around the north
side of the center.
Satellite imagery, however, showed that Howard made somewhat of a
comeback on the 24th. The eye at this time was very large--about 50
to 60 nm in diameter. The storm presented a distinct doughnut-like
appearance in satellite pictures. Winds reached 125 kts once more at
0600 UTC on 25 Aug when the hurricane was centered about 600 nm
southwest of Cabo San Lucas. The eye at this time was about 30 nm in
diameter with a 60 nm-wide ring of surrounding convection of -70 to
-75 deg C cloud tops. By this time, however, Howard was approaching
SSTs of 25 deg C, and a fairly rapid weakening trend soon set in.
The hurricane was downgraded to a tropical storm at 0000 UTC on
28 Aug when located about 950 nm west-southwest of Cabo San Lucas, and
was further reduced to depression status at 29/1200 UTC. The final
advisory at 1800 UTC placed the weakening depression far to the west
of the Mexican coast, near 20N, 133W. The remnants of Howard drifted
westward into the Central North Pacific area on 31 Aug and occasionally
produced some limited convective activity into the first couple of
days of September, but showed little indication of re-intensifying.
On 2 Sep the weak system appeared to merge into the ITCZ several
hundred miles to the southeast of Hawaii.
***********************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for August: 1 tropical storm **
2 typhoons **
** This based upon JTWC's classifications--JMA did not classify Otto
as a typhoon.
NOTE: Most of the information on each cyclone's history presented in
the narrative will be based upon JTWC's advisories, and references to
winds should be understood as a 1-min avg MSW unless otherwise noted.
However, in the accompanying tracking document I have made comparisons
of coordinates with JMA (Japan) and the Philippines (PAGASA) when their
positions differed from JTWC's by usually 40-50 nm or more. Also, as
announced earlier in a separate posting, a column of 10-min avg MSW
is included--the values being obtained from either PAGASA's or JMA's
advisories. A special thanks to Michael V. Padua, owner of the Typhoon
'98 webpage, for sending me the PAGASA tracks. Also some information,
primarily on the pre-depression stages of the various cyclones, was
taken from the Monthly Report of the RSMC, Darwin, Northern Territory,
Australia. A special thanks to Sam Cleland for forwarding that report
to me.
In the title line for each storm I plan to reference all the cyclone
names/numbers I have available: JTWC's depression number and name (if
any), JMA's tropical storm numeric designator, and PAGASA's name for
systems forming in or passing through their area of responsibility.
Typhoon Otto/Bising (TC-04W / STS 9802)
1 - 5 August
----------------------------------------
A tropical LOW developed in the Philippine Sea from a mesoscale
convective complex in early August. This was west of a TUTT which
helped to provide favorable upper-level divergence over SSTs exceeding
30 deg C. A scatterometer pass at 01/1411 UTC indicated winds of
around 30 kts. JTWC issued the first depression advisory at 0000 UTC
on 2 Aug, locating the center about 325 nm east of Manila. (It should
be noted that PAGASA issued the first bulletin on Tropical Depression
Bising 12 hrs earlier. The companion tracking file reflects this.)
Tropical storm intensity was reached at 1200 UTC on 2 Aug about 215
nm east of Manila. Initially, Otto/Bising was a small system with
gales covering an area less than 100 nm in diameter. After drifting
very slowly westward during the formative stages, the storm began to
moved northward, then north-northwestward in the general direction
of Taiwan. JTWC upgraded Otto/Bising to a minimal typhoon at 03/1200
UTC when the center was about 125 nm north-northeast of the northern
tip of Luzon. (It should be noted that JMA never assigned typhoon
status to this system, but treated it as a severe tropical storm.)
Otto/Bising remained a rather small system with storm-force winds
covering an area less than 40 nm in diameter and gales extending out
from the center no more than 65 nm. The typhoon reached the southeast
coast of Taiwan about 100 nm south-southwest of Taipei around 0600 UTC
on 4 Aug, moving north-northwestward. Otto weakened briefly to a
tropical storm after crossing the island, but regained minimal typhoon
intensity shortly before reaching the coast of China. Typhoon Otto
appeared to make landfall in Fukien Province, near Fuchou. (Please
forgive me if this spelling is incorrect or has changed--these names
were taken from an old atlas.)
The system weakened rapidly and began to dissipate once inland. For
some comments regarding the possible impact of Otto on the severe river
flooding occurring in China, refer to the discussion on Tropical Storm
Penny which follows.
Tropical Storm Penny/Klaring (TC-05W / STS 9803)
6 - 11 August
-------------------------------------------------
As Typhoon Otto was crossing the Chinese coast, another tropical
LOW formed in the Philippine Sea in a manner similar to the pre-Otto
disturbance. JTWC issued the first depression advisory at 06/0600 UTC
locating the center about 425 nm east-southeast of Manila. Mid-level
steering had a pronounced easterly component and the depression moved
northwestward toward the northern tip of Luzon. PAGASA issued the
first advisory at 07/0000 UTC, naming the system Klaring, while JTWC
upgraded the system to Tropical Storm Penny at 1800 UTC when the storm
was centered about 175 nm northeast of Manila. Penny/Klaring crossed
over the northernmost end of Luzon into the South China Sea and
temporarily weakened into a depression. JTWC upgraded the system back
to tropical storm status at 1800 UTC on 18 Aug.
After reaching the South China Sea, Penny/Klaring moved on a general
west-northwesterly course until it was about 115 nm south of Hong Kong.
At that point the storm turned to more of a westerly track and reached
an intensity of 50 kts at 10/1200 UTC when located about 150 nm
southwest of Hong Kong. Shortly afterward, Penny turned to the north
and made landfall in southern China just east of the Luichow Peninsula.
Peak intensity of 55 kts was reached shortly before landfall. Once
inland the storm began to quickly weaken and dissipate.
Massive flooding along the Yangtze River and perhaps other rivers
in China had been in progress for several weeks before the arrival of
Otto and Penny. The author scanned several press articles covering
the flooding but was unable to find any details of specific effects
of these two tropical systems. No doubt the flooding was exacerbated
to some degree from the rainfall attending Otto and Penny, but it is
probably impossible to specify exactly the magnitude of their effects.
Typhoon Rex/Deling (TC-06W / TY 9804)
24 August --->
--------------------------------------
What was to become the Northwestern Pacific's longest-lived cyclone
to date this season began in a weak monsoon trough which extended from
China to the Philippine Sea during an active phase of the Intraseasonal
Oscillation (ISO). A LOW formed in the trough on 22 Aug, but the first
depression advisories were not issued until 0000 UTC on the 24th when
both JTWC and JMA began issuing advisories. TD-06W was initially
located about 375 nm south-southeast of Okinawa. (PAGASA initiated
advisories on the depression at 0600 UTC and named it Deling, but the
system moved north of 25N and out of their AOR within 24 hours.)
The tropical depression moved slowly to the north-northeast and was
upgraded to Tropical Storm Rex at 25/0000 UTC. Rex's northeastward
motion came to a halt around 1800 UTC that day when centered about 350
nm east-southeast of Okinawa. The storm began to drift a little south
of due east for a couple of days, during which time it strengthened
into a typhoon. Estimated MSW reached 100 kts at 1200 UTC on 27 Aug
when Typhoon Rex was located about 100 nm west-northwest of Iwo Jima.
Rex began to curve to the north on the 27th and reached its peak
intensity of 115 kts about 150 nm north-northwest of Iwo Jima at 0600
UTC on 28 Aug.
By 30/0600 UTC the MSW had come down a bit to 90 kts and Rex began
to drift to the east-northeast from a position about 350 nm south-
southeast of Tokyo. This slow east-northeastward motion continued
through 0600 UTC on the 31st, after which Rex began to drift on an
unusual east-southeastward course. At 0000 UTC on 1 Sep Typhoon Rex
was still a 90-kt typhoon located about 500 nm southeast of Tokyo.
Next month's summary will continue the saga of Typhoon Rex as well
as provide some more details on the atmospheric circulation features
which led to Rex's most unusual track.
***********************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for August: No tropical cyclones
***********************************************************************
SOUTH INDIAN OCEAN (SIO) - South Indian Ocean West of Longitude 90E
Activity for August: No tropical cyclones
EXTRA FEATURE - NAMES FOR THE 1998-1999 SEASON
The tropical cyclone season in the South Indian Ocean is considered
to run from 1 August to 31 July of the following year. The names for
the upcoming season are:
Alda, Birenda, Chikita, Davina, Evrina, Francine, Genila,
Helvetia, Irina, Jocyntha, Kristina, Lina, Marsia, Naomie,
Orace, Patricia, Rita, Shirley, Tina, Veronique, Wilvenia,
Yastride
***********************************************************************
AUSTRALIAN REGION (AUG) - From Longitude 90E Eastward to Longitude 160E
Activity for August: No tropical cyclones
NOTE: I had planned to include some comments by Dr. Jack Beven of
TPC/NHC and Dr. Greg Holland of Australia's Bureau of Meteorology
regarding an interesting hybrid storm system along the New South
Wales coast. Due to the great length of this summary, I am going to
hold this for a couple or three months until we reach a month without
quite so much tropical cyclone activity to cover.
***********************************************************************
SOUTHWEST PACIFIC (SWP) - South Pacific Ocean East of Longitude 160E
Activity for August: No tropical cyclones
***********************************************************************
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
August as an example: aug98.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 August summary is the eleventh 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: aug98.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
***********************************************************************
***********************************************************************
|
Document: summ9808.htm
Updated: 18th March 2008 |
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