Hurricane Howard is estimated to have been the strongest
hurricane of the 1998
eastern North Pacific hurricane season.
The hurricane remained over water its entire lifetime
without any direct effects to land.
a. Synoptic History
Howard can be traced back to a tropical wave
that emerged from the west coast of Africa
on 7 August. The wave spawned intermittent clusters of convection as it moved across the Atlantic at
low latitudes, and then remained rather nondescript during its passage over the Caribbean Sea and the
northern portions of South America. Cloudiness and convection increased off the Pacific coast of
Central America on 17 August.
The first satellite classifications were received on 18 August. Animation of satellite
imagery indicated a broad low-level cyclonic circulation with intermittent bursts of deep convection on
the 18th and 19th. The deepest convection became more persistent near the circulation
center, and the "best track"
indicates that a tropical depression formed from the
disturbance near 0600 UTC 20 August
while centered about 300 n mi south of Puerto Angel, Mexico (Fig. 1
[29K GIF] and Table 1). The tropical cyclone
moved generally west-northwestward near 10 knots in response to deep-layer-mean steering.
Banding features became more pronounced and the depression strengthened into
Tropical Storm Howard at 0000 UTC 21 August while centered about 375 n mi south of Acapulco,
Mexico. The center of the tropical cyclone became more centrally embedded within deep convection
and Howard became a hurricane at 1800 UTC 21 August while centered about 450 n mi south-southeast
of Manzanillo, Mexico. The upper-level outflow became better established, and Howard continued to
intensify as evidenced by the appearance of an eye in satellite imagery on 22 August. Rapid
strengthening occurred and Howard became a category three hurricane on the
Saffir/Simpson Hurricane Scale by 1200 UTC on this date.
It is estimated that Howard reached its peak intensity of 130 knot one-minute surface winds
and 932 mb minimum central pressure near 0000 UTC 23 August while centered about 525 n mi south-southeast of the southern
tip of Baja California. Howard's intensity neared the top end of category four, with a small-diameter eye embedded
within a very cold central dense overcast. Although the eye gradually became larger and some intensity
fluctuations occurred, Howard appears to have remained a major hurricane (category three or higher) for
four days.
Howard moved over cooler water and weakened to a tropical storm by 0000 UTC 28
August while centered about 950 n mi west-southwest of the southern tip of Baja California. The
cyclone weakened to a tropical depression at 1200 UTC 29 August
while centered about 1200 n mi west-southwest of the southern tip of Baja California
and is considered to have dissipated on 30 August--although a low-level cloud swirl persisted for a few more days.
b. Meteorological Statistics
Figures 2 (19K GIF) and
3 (19K 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. As usual for
an eastern Pacific tropical cyclone, satellites provided the primary source of observational data.
Dvorak technique location and intensity estimates from the satellite data
were produced by the Air Force Weather Agency (AFGWC in figures), the NOAA
Synoptic Analysis Branch (SAB) and the NOAA
Tropical Analysis and Forecast Branch (TAFB). The highest official Dvorak T number was 6.5
(127 knots) from TAFB and SAB. However, the highest objective Dvorak T
number using an experimental program developed by the University of Wisconsin was 7.0 (140 knots)
between 1345 UTC 22 August and 0300 UTC 23 August. The highest 12-hour weighted-average objective Dvorak
T number peaked at 7.0 near 0000 UTC 23 and is the basis for estimating the peak intensity at this time.
The maximum wind in the best track is between the official and experimental estimates.
c. Casualty and Damage Statistics
There were no reports of casualties or damage from Howard received at the NHC.
d. Forecast and Warning Critique
The NHC average official track forecast errors for Howard (excluding the tropical
depression stage) were 34 (32 cases), 68 (30 cases), 95 (28 cases), 125 (26 cases) and 199 n mi (22
cases), respectively, for the 12-, 24-, 36-, 48- and 72-hour forecast periods. These were all similar to the
1988-1997 average errors of 39, 71, 105, 137 and 195 n mi for the same time periods. The NHC average
official track forecast errors were similar to the averages from the operationally available track
prediction models through 48 hours. Surprisingly, the AVNI, GFDI, UKMI, CLIP, BAMD, BAMM and
BAMS guidance models all had average track forecast errors somewhat less (21 to 62 n mi) than the
average official forecasts at 72 hours.
The NHC official intensity forecasts showed a distinct negative bias (i.e., intensity was
underestimated) while Howard was strengthening and a distinct positive bias (i.e., intensity was
overestimated) while Howard was weakening. The largest intensity forecast error occurred 36 hours
prior to peak intensity and was 50 knots too low.
Watches and warnings were neither issued nor necessary for Howard.
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