a. Synoptic History
Olaf was a tenacious tropical cyclone
which persisted for a couple of weeks despite a prevailing unfavorable upper-level
environment.
Olaf appears to have developed from an area of disturbed
weather associated with a tropical wave that crossed Central
America on 22 September and then slowly moved westward over the
eastern Pacific. The
disturbance became nearly stationary while the
shower activity gradually increased. During that time, there was a
strong upper-level low over the Gulf of Mexico that moved southwest
into the eastern Pacific, to the west of the disturbance.
Initially, the strong upper-level winds associated with the low
produced a shearing environment which inhibited significant
development of the disturbance. A sequence of satellite images
clearly showed how the disturbance was able to gradually develop
its own upper-level outflow which eventually forced the upper-low
from to retreat its vicinity. This resulted in the formation of
tropical depression
near 1200 UTC 26 September, about 300 n mi south of the Gulf of Tehuantepec.
It became Tropical Storm Olaf a
few hours later.
The upper-low which also helped to steer the tropical cyclone
slowly northward, toward the southeastern coast of Mexico. During
that period, both satellite intensity estimates and ship reports
indicated that Olaf was strengthening. Olaf reached estimated
maximum winds of 60 knots and a minimum
pressure of 989 mb at 1800 UTC 27 September. Thereafter, a portion
of the circulation began to interact with rough terrain and Olaf
gradually weakened. It was a tropical depression when the center
reached the coast in the vicinity of Salina Cruz 0000 UTC 29
September. A few hours later, the circulation was no longer
identified and operationally Olaf was declared dissipated.
However, the area of disturbed weather, associated with the
remnants of Olaf moved westward over water for a few days and
operationally was reinstated as a tropical depression status 5
October. Olaf was then located a few hundred miles southwest of
the southern tip of Baja California. A post-storm analysis of the
satellite imagery suggests that a weak surface circulation with
estimated 25-knot winds and some
convective activity persisted, and were sufficient to redesignate
the system as a tropical depression from 29 September to 5 October.
Olaf began to move toward the southeast on the 8th, embedded
within a much larger cyclonic circulation which prevailed over the
area south of Mexico. The depression moved toward the north and
made its final landfall near Manzanillo Mexico 12 October. It
weakened over the high terrain, but cloudiness and showers
associated with this system moved back over water. It failed to
redevelop.
Olaf's track is shown in Fig. 1. (21K 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 (12K GIF) and
3 (11K GIF) and are based on satellite intensity
estimates from the Tropical Analysis and Forecast Branch (TAFB),
the Synoptic Analysis Branch
(SAB) and the Air Force Global Weather
Center (AFGWC).
Ship OUJH2 was near Olaf for several hours and it was
able to send a few valuable observations. The vessel reported maximum winds of
55 knots and a minimum pressure of 1003.5
mb at 0300 UTC 27 September when was located just west of the
center of Olaf. This observation was used to estimate the maximum
intensity of Olaf.
c. Casualty and Damage Statistics
Preliminary reports from Mexico indicate that strong winds
and heavy rains associated with Olaf bashed Mexico's Pacific
southeast coast. Media reports said that the military and
government officials from Mexico were searching for three fishing
vessels missing off the coast of Acapulco. Heavy rains also
affected Guatemala and El Salvador where floods were reported.
There are no reports of damage associated with Olaf's second
landfall.
d. Forecast and Warning Critique
Olaf moved northward following its inception. Therefore, a
tropical storm warning was issued for the
coast of Mexico from Tapachula to Punta Maldonado at 2100 UTC 26 September. Because
Olaf was forecast to become a hurricane
before landfall, the tropical storm warning was replaced by a
hurricane warning for the same region at 0900 UTC 27 September.
Olaf unexpectedly weakened and the hurricane warnings
were changed back to tropical storm warnings later on that day.
The average official forecast error was 89 n mi at 24 hours
(5 forecasts) and 93 n mi at 72 hours (1 forecast). These numbers
are not significant since Olaf was a tropical storm only for a
short period.
Advisories
on Olaf were discontinued after its first landfall but the
possibility of its regeneration was indicated in the NHC
Tropical Weather Outlooks.
Advisories were reinitiated when it became apparent that
Olaf had rejuvenated.
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