a. Synoptic History
A category 2 hurricane on the Saffir/Simpson Scale
strikes the southern tip of Baja California.
Henriette formed from a tropical wave
that moved westward across the west coast of Africa on 15 August. The wave traversed
the Atlantic, the Caribbean and Central America and reached the
eastern Pacific by the 29th of August. Over the next few
days it acquired considerable deep convection and a low-level circulation.
It became a tropical depression on 1 September
while centered about 150 n mi off the southwest coast of Mexico. Henriette's track
begins here and is shown in Fig. 1 (42K GIF);
six-hour track positions, maximum one-minute wind speeds and minimum sea level pressure are
listed in Table 1.
The depression moved northwest and then northward during the
next two days and its motion slowed. It strengthened to a
tropical storm
on the 2nd and to a hurricane
on the 3rd, while its center
moved within 100 n mi of the mainland near Puerto Vallarta.
Henriette turned back toward the northwest and accelerated and its
center moved to the extreme southern tip of Baja California at mid
day on the 4th. A well-defined eye
formed and the hurricane is estimated to have reached its peak intensity of
85 knots at 1200 UTC on the 4th when the northern
eyewall moved over land.
By the 5th, the hurricane was turning toward the west and
moving away from land. It gradually weakened over the next three
days. There was only a swirl of low clouds left to track by the
7th and 8th, about 900 n mi west of Baja California.
b. Meteorological Statistics
Figures 2 (26K GIF)
and 3 (28K GIF)
show the curves of minimum sea-level pressure
and maximum one-minute wind speed as a function of time, along with
the data on which they are based. No reports have been received
from the area of Baja California that experienced hurricane
conditions. Except for ship reports, all of the data in both
figures are satellite-based estimates.
The ship WLDF reported 70-knot sustained winds,
from 03-0500 UTC on the 3rd and while located about 20 n mi northeast of the
center. This was the basis for operationally upgrading Henriette
to a hurricane as the highest satellite-based estimates were 55
knots prior to the ship report. Ship reports of tropical storm
winds or higher are listed in Table 2.
c. Casualty and Damage Statistics
It is estimated that sustained winds of 85 knots
affected the extreme southern tip of the peninsula. There was heavy road damage
(from storm surge flooding) in the state of Baja California Sur and
800 people were forced from their homes, according to Mexican
officials. Agriculture was adversely affected. Up to ten inches
of rainfall may have occurred, based on estimates from satellite
imagery. No deaths have been reported.
d. Forecast and Warning Critique
The average official track errors ranged from 86 n mi at 24
hours to 180 n mi at 48 hours to 158 n mi at 72 hours. Except for
72 hours, the average errors are a little higher that the long-term
averages since 1988. The largest track errors are from forecasts
made on the 4th when the hurricane was moving northwestward near
Baja California. The forecasts were biased to the north and too
slow in anticipating the accelerating westward movement which
followed. The 72-hour forecasts made at this time did not verify
as Henriette weakened to a depression on the 7th.
There were some 30-35 knot negative errors of the 24-hour wind
speed forecasts issued on the 2nd. These forecasts did not
correctly anticipate the strengthening that occurred on the 3rd.
A tropical storm watch
was issued by the government of Mexico for Baja California south of La Paz at 2100
UTC on the 2nd. This was changed to a hurricane watch
at 0430 UTC on the 3rd and to a hurricane warning
at 2100 UTC. The hurricane warning was extended
northward to 25 degrees north latitude at 0900 UTC on the 4th.
Warnings were discontinued 24 hours later. Landfall is estimated
at 1500 UTC on the 4th, so the hurricane watch provided about 34
hours lead time and the warning gave 18 hours lead time. The lead
times to the onset of tropical storm conditions are, of course,
somewhat less.
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