a. Synoptic History
The origin of Gustav is tracked back to an area of disturbed weather
that moved from Africa to the Atlantic Ocean on 24 August accompanied
by a low-level cloud circulation. This was the third of three closely-spaced
tropical cyclones which included Hurricanes
Edouard and Fran.
The disturbed weather gradually became better organized and a
formed from this weather on the 26th just south of the Cape Verde Islands. The
best track begins on the 26th,
as indicated in Table 1 and
Fig. 1 (32K GIF).
The depression moved west-southwestward at about 12 knots for two
days, under the steering of a ridge of high pressure to its north.
The motion turned toward the northwest on the 28th in response to a
mid Atlantic trough. The trough became a cut-off low which continued
to steer the storm northwestward for about five days, after which
dissipation occurred. The maximum intensity of Gustav is estimated at
40 knots on the 29th. A limiting factor in the storm's development
was originally the outflow from Hurricane Fran which interfered
with the organization of convection during the 26th and 27th. Then the
cut-off low mentioned above produced a shearing environment which
eventually led to Gustav's dissipation on the 2nd of September.
b. Meteorological Statistics
Figures 2 (27K GIF)
and 3 (28K GIF)
show curves of minimum sea-level pressure and maximum one-minute surface wind
speed, respectively, as a function of time. Satellite data plotted in these
figures is based on the Dvorak satellite
intensity estimating technique as applied at the
Tropical Analysis and Forecast Branch (TAFB), the
Satellite Analysis Branch (SAB) and the
U.S. Air Force Global Weather Center
(AFGWC). There were no ship reports of tropical storm
force winds in association with Gustav.
c. Casualty and Damage Statistics
Gustav remained in the central tropical Atlantic Ocean during its
existence and did not affect land.
d. Forecast and Warning Critique
The average official track forecast errors for this storm ranged from
64 nautical miles at 24 hours(14 cases) to 157 miles at 72 hours(6
cases). These values are considerably smaller than the previous 10-year
average of official track forecast errors which range from 93
nautical miles at 24 hours to 273 nautical miles at 72 hours.
On the 28th and 29th, there were several official forecasts that
brought the wind speed to 60 knots in 72 hours. Since this
strengthening failed to materialize, there was a positive bias to the
official wind speed forecast errors.