a. Synoptic History
A poorly defined tropical
wave crossed Central America during the 7th and 8th of June, accompanied
by cloudiness and a few thunderstorms. The wave moved westward, and a broad
low to middle level circulation developed a few hundred miles south of
the Gulf of Tehuantepec, Mexico. However, the convection was disorganized
and well removed from the smaller centers
of circulation which were embedded within the system. Gradually,
a dominant center of circulation became better defined and banding features
developed and it is estimated that the system reached tropical
depression status at 1200 UTC 11 June. Historically, the median day
for the formation of the first eastern North Pacific tropical depression
is around 31 May.
The depression did not change much in organization for the
next couple of days. Thereafter, another tropical wave merged within
the circulation of the depression and strengthening occurred. The system
then reached tropical storm status.
Agatha's peak winds were estimated to be 55 knots
at 0000 UTC 14 June, just before the cyclone
moved over cooler waters. This estimate was based on intensity
estimates of 3.5 on the Dvorak scale
from the Tropical Analysis and Forecast Branch
(TAFB). Thereafter, gradual weakening began.
A very strong middle level ridge was anchored from the Gulf
of Mexico and extended westward across the Baja California peninsula. This
ridge provided a pattern which steered Agatha on a general west northwest
track through most of its lifetime.
Agatha's track is shown in Fig.
1 (17K 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 (19K
GIF) and 3 (20K GIF) and are based
on satellite intensity estimates from TAFB,
the Satellite
Analysis Branch (SAB) and the Air
Force Global Weather Agency (AFGWA).
c. Casualty and Damage Statistics
There were no reports of casualties or damage associated
with Agatha.
d. Forecast and Warning Critique
Agatha was a tropical storm for only two days. Therefore,
an evaluation of the average forecast errors would not be meaningful.
Global models, specifically the Aviation Model, forecast
the development of another tropical cyclone to the east of Agatha. Consequently,
models which were based of the Aviation output for steering showed a leftward
track bias during the days when the Aviation Model was developing the unrealistic
storm. Also, there was a possibility that the tracking algorithm gathered
one of the spurious vortices not related to Agatha resulting in an incorrect
forecast track. The GFDL model insisted
on weakening the storm too quickly while SHIPS forecasts were more
realistic. SHIPS wrongly brought Agatha to hurricane strength but it was
able to capture the rapid weakening due to the influence of cool waters.
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