Humberto coexisted with four other
tropical cyclones
(Iris, Karen,
Jerry and Luis)
in the Atlantic basin. The hurricane
traveled several days through the open Atlantic without hitting land.
a. Synoptic History
Hurricane Humberto developed from one of the several strong
tropical waves that moved off the
coast of Africa in August of 1995. In fact, Dakar, Senegal reported 50 knot
winds at 500 mb when the axis of the wave crossed that station on 19 August.
Humberto was preceded by a strong tropical wave which eventually
became Iris and followed by another strong wave which triggered
Karen.
Satellite images and surface reports indicated a broad
cyclonic rotation associated with this weather system from the time
it moved off the west coast of Africa. However, the convection was
disorganized and displaced to the southwest of the circulation
center
due to the prevailing northeasterly shear. Once the system
moved westward over warmer waters and into an area of lighter
shear, it developed rapidly. A post-analysis of satellite images
suggests that it became tropical depression
at 0000 UTC 22 August and reached tropical storm
status six hours later. Under an upper-level environment very favorable for development, Humberto became
a hurricane at 0600 UTC 23 August.
Humberto's motion was rapidly influenced by a middle-level
trough over the central Atlantic (Fig. 1 [95K GIF])
and turned northward and northeastward over open waters. Humberto maintained hurricane
status until the 31st when it weakened to a tropical storm. It was
rapidly absorbed by an extratropical low early on the 1st of September.
Just before Humberto began the northwestward turn, it reached
its estimated peak intensity of 95 knots and a minimum pressure of
968 mb. This occurred at 1800 UTC 24 August when intensity
estimates from the National Hurricane Center and the
Satellite Analysis Branch
(SAB) reached 5.5 and 5.0 on the
Dvorak scale.
Thereafter, the hurricane weakened some, primarily due to
interference with the outflow produced by Iris. Once Humberto
moved away from Iris, it reintensified and turned northeastward
ahead of the extratropical
cyclone which eventually absorbed it.
Humberto's track is shown in Fig. 2 (95K GIF).
Table 1 is a listing, at six-hour 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,
shown in Figures 3 and 4 (47K GIF),
are primarily based on satellite intensity estimates from the National Hurricane Center (NHC),
SAB and the
Air Force Global Weather Central (AFGWC). The vessel
DBRUK4 was under the influence of Humberto for about 48 hours and
experienced tropical storm force winds throughout that period.
There was a report from that vessel of 60-knot winds from the
southeast and a pressure of 1005 mb at 1800 UTC 30 August. At that
time, the ship was about 20 n mi north of the center of the
hurricane. Table 2 shows observations from ships that
encountered 34 knot or higher winds speeds associated with Humberto.
c. Casualty and Damage Statistics
There were no reports of injuries, deaths or damage associated with Humberto.
d. Forecast and Warning Critique
A post-analysis of satellite images suggests that advisories on
Humberto could have been initiated, perhaps, a few hours earlier.
However, the location and intensity of incipient tropical systems
on infrared images is uncertain. Unless surface observations are
available, if a system is in a formative stage, the NHC often waits
for the more accurate estimates obtained from visible imagery to
initiate advisories.
The individual errors of each track model as well as the errors
of the official forecast are included in Table 3.
The official forecast was comparable with the past 10-year average and slightly
better than average for the 48- and 72-h period. The tropical
cyclone intensified faster than forecast during the early stage.
Thereafter, once Humberto became a hurricane, it did not intensify
as much as forecast and during the decaying phase, Humberto
weakened slower than expected.
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