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Preliminary Report
Hurricane Alma
20 - 27 June 1996

Lixion A. Avila
National Hurricane Center
24 July 1996


PRELIMINARY REPORTS
Unnamed Tropical Storm
Tropical Depression 2-E
Hurricane Alma
Hurricane Boris
Tropical Storm Cristina
Tropical Depression 6-E
Hurricane Douglas
Tropical Storm Elida
Hurricane Fausto
Tropical Storm Genevieve
Hurricane Hernan
Tropical Depression 12-E


TROPICAL PREDICTION CENTER/ALMA96 PRELIM

 Visible image of Hurricane Alma pounding the southwest coast of Mexico.


[1996 Atlantic Hurricane Season]

Hurricane Alma, the first hurricane of the 1996 eastern north Pacific hurricane season, hit the southwestern coast of Mexico causing at least three direct deaths.



a. Synoptic History

Alma, the first named tropical cyclone of the 1996 eastern north Pacific hurricane season developed about 240 n mi south of Acapulco Mexico. Although it is difficult to identify the origin of this disturbance, it appears to be related to the southern extension of the same tropical wave which triggered Tropical Storm Arthur in the Atlantic. The incipient disturbance crossed from the southwestern Caribbean to the eastern pacific between the 17th and the 18th of June as indicated by upper-air observations from Central America and satellite images. This disturbance was accompanied by an anomalous upper-level anticyclone (200 mb) as shown in Fig. 1a (100K GIF).

The disturbance moved into the eastern Pacific over warmer than normal waters. Initially, stronger than normal 200 mb northeasterly winds and 850 mb southwesterly winds prevailed as indicated in Figs. 1b and 1c (100K GIF). This pattern resulted in a shearing environment and a low-level center located to the northeast of the convection. However, the shear was not strong enough to prevent strengthening and the deep convective activity gradually became aligned with the low-level center. Then, a tropical depression formed at 0000 UTC June 20 and reached tropical storm intensity by 1800 UTC as indicated by satellite intensity estimates.

When the shear relaxed, Alma intensified and became a hurricane at 0000 UTC 22 June while moving on a general northwest track. A mid-level trough located in the vicinity of Baja California in combination with a mid-to upper- level low over the southwestern Gulf of Mexico steered Alma slowly northward toward the southwest coast of Mexico. On that heading, Alma reached its maximum intensity of 90 knots and minimum pressure of 969 mb at 1200 UTC 23 June. At that time, objective and subjective T-numbers were oscillating near 5.0 on the Dvorak scale. Figure 2 (494K GIF) is a visible satellite image of Hurricane Alma just prior to landfall.

The steering flow collapsed and Alma began to drift near the coast. Alma made landfall near the town of Lazaro Cardenas but it did not move farther inland. The center moved back over water but a portion of the circulation was involved with land. Alma meandered for another 36 hours near the coast and never reintensified. Apparently, the inner core circulation was severely disrupted by the steep topography of Mexico. It gradually weakened until dissipation while moving slowly on a track parallel and not far from the coast.

Alma's track is shown in Fig. 3 (36K 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 4 (22K GIF) and 5 (24K GIF) are based on satellite intensity estimates from the Tropical Analysis and Forecast Branch of the Tropical Prediction Center (TAFB), and denoted as TSAF in the figures. It was also used estimates from the Satellite Analysis Branch (SAB) and the Air Force Global Weather Central (AFGWC). Alma was an intense hurricane with a very small diameter. The strongest winds were concentrated within a small area surrounding the eye. This was suggested by sparse surface observations within the area of influence of Alma, as well as satellite images. Images from Acapulco and Cuyutlan radars, provided by the "Servicio Meteorologico Nacional de Mexico" confirmed that Alma was a small diameter tropical cyclone. These radar images, received in near real-time, were extremely useful to track Alma. There are no reports of measured strong winds received at this time. Manzanillo reported 68.8 mm of rainfall in 24 hours.


c. Casualty and Damage Statistics

Newspapers reports from Mexico stated that three people were killed by Alma in a small town near Lazaro Cardenas when their house collapsed. Numerous houses were damaged and power failed in various coastal towns where roads were covered by debris and water. In Zihuatanejo, several houses and trees were also damaged. There are unconfirmed reports (Miami Herald, June 25, 1996) that at least 17 people were killed by flooding in Puebla, about 300 n mi to the east of the landfall point. These rains were probably related to Alma.


d. Forecast and Warning Critique

Table 2 shows the preliminary forecast errors for Hurricane Alma. The official forecast errors were by far much smaller than the 1985-1994 average, and generally better than the track models. The purely dynamical models performed poorly, in particular the AVN and GFDL models. One attributes such large errors produced by dynamical models to the lack of upper-air data over the ocean south and west of the hurricane. Mexican upper-air data were available at all times during Alma. Numerical track forecast by the "Universidad Autonoma de Mexico" were of comparable accuracy to U.S. dynamical models. However, model output from Mexico was received at the NHC only twice during Alma.


 
Table 1. Preliminary best track, Hurricane Alma, 20-27 June, 1996.
Date/Time
(UTC)
Position Pressure
(mb)
Wind Speed
(kt)
Stage
Lat. (°N)Lon. (°W)
20/000013.198.7100930TD
060013.599.3100930"
120013.999.9 100730"
180014.4100.3100535TS
21/000014.9100.7100240"
060015.4101.1100045"
120015.7101.5 99750"
180015.8102.099455"
22/000015.8102.498765H
060015.9102.798575"
120016.2102.697885"
180016.6102.697585"
23/000016.7102.897285"
060016.9102.997085"
120017.2102.896990"
180017.5102.697090"
24/000018.0102.497390"
060017.8102.6975 80"
120017.7102.897965"
180017.7102.898560TS
25/000017.6102.799555"
060017.5102.4100045"
120017.3102.5100535TS
180017.3102.7100930TD
26/000017.4102.9100930"
060017.5103.5100930"
120017.7104.0100930"
180018.0104.5100930"
27/000018.4105.0100925"
060018.7105.5100925"
120018.9106.2   Dissipating
 
23/120017.2102.896990 Minimum Pressure
24/000018.0102.497390 Landfall
(Near Lazaro Cardenas)

TD: Tropical Depression

TS: Tropical Storm

H: Hurricane

D: Dissipating


 
Table 2
Preliminary forecast evaluation Hurricane Alma
Heterogeneous sample (Errors in nautical miles for tropical storm and hurricane stages with number of forecasts in parenthesis)
Forecast TechniquePeriod (hours)
1224364872
OFCI40 (18)67 (16)94 (14)109 (12)129 ( 8)
AVNI39 (16)69 (14)131 (12)220 (12)467 ( 8)
GFDI131 (13)210 (11)276 ( 7)306 ( 5)302 ( 1)
CLIP36 (18)69 (16)109 (14)153 (12)310 ( 8)
BAMD48 (18)77 (16)101 (14)132 (12)160 ( 8)
BAMM49 (18)77 (16)104 (14)129 (12)159 ( 8)
BAMS43 (18)69 (16)88 (14)98 (12)141 ( 8)
NHC Official34 (18)65 (16)89 (14)112 (12)129 ( 8)
NHC Official
(1988-95 8-yr average)
3971105139 196



Brian Maher
Jack Beven

Last updated December 26, 1998