Hurricane Ismael, a short-lived Category 1
hurricane on the
Saffir/Simpson Hurricane
Scale that made landfall near Topolobampo, Mexico, resulted in a large
loss of life in the Gulf of California.
a. Synoptic History
Satellite imagery showed a poorly organized area of
cloudiness and showers centered about 150 n mi south of the coast
of Guatemala on 9 September. The tropical
disturbance moved slowly west-northwestward for the next couple of days
without signs of development. On 12 September a cloud system
center became evident in satellite imagery,
and analysts from both the
NESDIS
Synoptic Analysis Branch (SAB) and the NHC began
Dvorak classifications at 1200 UTC on
this day.
Convective banding became organized and the
"best track"
(Figure 1 [48K GIF]
and Table 1) indicates that a
tropical depression
formed at 1800 UTC 12 September about 300 n mi south-southwest of
Manzanillo, Mexico. The depression began to move toward the
northwest near 7 knots.
Deep convection increased near the center, and satellite
intensity estimates suggest that the depression strengthened into
Tropical Storm
Ismael at 0000 UTC 13 September. The storm turned more toward the north,
apparently in response to a mid- to upper-level low over Baja California
observable in water vapor imagery.
Upper-level outflow became well-established as deep
convection continued to develop on 13 and 14 September. It is
estimated that Ismael strengthened into a hurricane while
centered about 250 n mi south-southeast of the southern tip of
Baja California at 0600 UTC 14 September. Satellite analysts at
both SAB and NHC indicated hurricane intensity at this time. On
the 14th a poorly-defined eye
became visible in satellite pictures, and Ismael is estimated to
have reached a maximum intensity of 70 knots
by 1200 UTC.
Forward motion of the hurricane increased to 18 knots on the
14th as the hurricane was steered by the mid- to upper-level
trough to the west and a deep-layer-mean ridge to the east.
Ismael made landfall near 0400 UTC 15 September in the vicinity
of Topolobampo, Mexico.
The tropical cyclone
weakened rapidly as the circulation
moved over the Sierra Madre Mountains of northern Mexico, and it
dissipated by 0000 UTC 16 September. However, considerable
moisture from Ismael quickly spread over the southwestern U.S.
and continued eastward through the mid-Atlantic states.
b. Meteorological Statistics
Best track positions and intensities were derived primarily from Dvorak
technique estimates. Figures 2 (20K GIF) and
3 (22K GIF)
show the curves of minimum central pressure and maximum one-minute wind speed,
respectively, versus time, along with the observations on which
they are based. Table 2 lists ship reports with
tropical storm force winds in the vicinity of Ismael.
c. Casualty and Damage Statistics
Newspapers reported 105 deaths and several more missing in
association with Ismael. According to limited records of
casualties along the west coast of Mexico available at the NHC,
this makes Ismael the fifth deadliest
eastern Pacific hurricane
this century. Many of those who died were on fishing boats that
encountered strong winds and high seas in the Gulf of California.
The Associated Press reported thousands homeless as a result of
the hurricane and about 5000 "rickety houses" destroyed. Some of
the worst damage was in the village of Topolobampo, Mexico,
located a few miles to the south of Los Mochis. Houses and
telephone poles were knocked down in Los Mochis, but no deaths
were reported there.
d. Forecast and Warning Critique
Since Ismael was a short-lived
cyclone, there were only a
limited number of official forecasts that were verified. During
the time when Ismael was a tropical storm or hurricane, the
average official track forecast errors were 57 (9 cases), 166 (7
cases), 311 (5 cases) and 445 (3 cases) n mi at 12, 24, 36 and 48
hours. These were two to three times as large as the NHC
historical (1988-1994) average, but not atypical for northward
moving storms.
In the early stages of Ismael, most track prediction models
indicated a westward or northwestward motion away from land (for
example, see Fig. 4 [68K GIF]).
Only the GFDL
model consistently predicted
a northward motion toward Mexico. Unfortunately, confidence in
the GFDL in the eastern Pacific was low due to experience with
previous storms which were erroneously forecast to move northward
by the GFDL. In 1994, the deep-layer BAM had the lowest forecast
errors at most time periods. The NHC official forecasts for
Ismael, even though large, were still less than the forecast
errors from the deep-layer BAM at all time periods. Although it
cannot easily be determined how many of the Mexican rawinsonde
data were included in the NMC
model initializations, forecasters received data from the closest upper-air
stations of Socorro, Mazatlan and Empalme intermittently. Data from Socorro and
Empalme were missing from NHC upper-air plots for 1200 UTC on 12-15
September and from Mazatlan at 0000 UTC on 13 September. No
upper-air soundings were taken from the Baja peninsula. This
lack of sufficient upper-air data likely contributed to poor
initializations. Even with complete Mexican rawinsonde data,
however, recurving storms near Baja are usually difficult to
forecast, in part due to the sparsity of upper-air data between
Mexico and Hawaii.
Intensity forecasts showed a slight negative bias (i.e.,
intensity was underestimated) on 13 September, and a positive
bias (i.e., intensity was overestimated) thereafter. The
positive bias was a result of the cyclone moving over land and
weakening faster than forecast.
Usual uncertainty exists in determining the best track
intensity when only satellite estimates are available. It is
interesting to note from Figure 3
that the intensity estimates from the
Air Force Global
Weather Central never exceeded 45 knots.
Table 3 lists the watches and warnings issued
by the Government of Mexico.
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