a. Synoptic History
Hermine developed from a tropical wave which crossed Dakar,
Senegal on 5 September and moved westward across the Atlantic. The
wave was void of significant thunderstorm activity until it reached
the Windward Islands where cloudiness and showers increased and
there was a large 24-h pressure change on 12 September. The wave
continued westward very close to the South American coast and then
moved northwestward through the Northwest Caribbean Sea and the
Yucatan Channel where a low pressure system developed. The system
began to interact with an upper low in the Gulf of Mexico and
another tropical wave which reached the area. During this period,
a large and well-defined monsoon-type flow prevailed over Central
America, the Northwestern Caribbean Sea and the Gulf of Mexico. It
was not until 1200 UTC 17 September that the system acquired enough
organization to be classified as a tropical depression.
The depression made a cyclonic loop over the central Gulf of Mexico
while interacting with the upper-low located in the Bay of
Campeche. The depression gradually became organized despite the
unfavorable upper-level wind shear which prevailed in the area and
reached tropical storm status at 1200 UTC 19 September.
Hermine moved on a general northward track and made landfall as a weakening
35-knot tropical storm near Cocodrie, Louisiana at 0500 UTC 20
Hermine's track is shown in Fig. 1 (15K GIF).
Table 1 is a listing, at six-hourly intervals, of the
best-track position, estimated minimum
central pressure and maximum 1-minute surface wind speed.
b. Meteorological Statistics
The best track pressure and wind curves as a function of time
are shown in Figs. 2 (15K GIF) and
3 (14K GIF) and are primarily based on data
from reconnaissance flights, WSR-88D data, surface observations and
satellite intensity estimates from the Tropical Analysis and Forecast Branch (TAFB),
the Satellite Analysis Branch (SAB) and the
Air Force Weather Agency, (AFGWC in figures). Hermine produced
rains of about .5 to 1 inches and there were no reports of tropical
storm force winds near the area of landfall.
c. Casualty and Damage Statistics
There are no reports of casualty and damage from Hermine.
d. Forecast and Warning Critique
Due to the uncertainties in the forecast while the tropical
cyclone was looping in the central Gulf of Mexico, it was necessary
to issue tropical storm watches and warnings for a large portion of
the Gulf coast. Tropical storm watches and warnings are summarized
in Table 2.
Hermine was a tropical storm for about 24 hours. Therefore, the
evaluation of the average forecast errors would not be meaningful.
Table 3. Watch and warning summary, Tropical Storm Hermine, September 1998.
||Tropical Storm watch issued
||Sargent, Texas to Grand Isle, Louisiana|
||Tropical Storm watch extended southward
||From Sargent, to Matagorda, Texas|
||Tropical Storm watch extended eastward
||to Pascagoula Mississippi|
||Tropical Storm watch discontinued
||west of High island, Texas.|
||Tropical Storm warning issued
||from Morgan City, Louisiana eastward to Pensacola Florida|
|Tropical Storm watch discontinued
||from east of Pensacola to Destin, Florida|
|Tropical Storm watch discontinued
||west of Sabine Pass, Texas|
||Tropical Storm warning extended westward
||from west of Morgan City to Intracoastal City, Louisiana|
||tropical Storm watch discontinued
||west of Intracoastal City|
||tropical storm warning and watch discontinued