a. Synoptic History
Hurricane Dolly formed from a tropical wave
of large lateral extent that moved from the west coast of Africa to the central
Caribbean Sea during 9-18 August 1996. Although the wave generated
deep convection when it emerged from Africa, there was little
accompanying thunderstorm activity for much of its passage across
the tropical North Atlantic Ocean. Deep convection redeveloped
when the wave reached the eastern Caribbean, but did not persist in
a concentrated pattern until the system was south to southwest of
Jamaica on the 18th-19th. A low- to mid-level cyclonic circulation
was then detected in data obtained during a
NOAA research flight
to study the development of tropical cyclones.
Satellite analysts indicated that the system was too weak to classify using the
Dvorak technique late
on the 18th, but they calculated Dvorak T-numbers of 1.5 and 2.0 on the afternoon
of the 19th. By mid-afternoon on the 19th, the first
by reconnaissance aircraft was made and data from the plane, satellite, and a ship
that reported 45 knots at 1800 UTC were used to estimate that the
stage began with a poorly-defined circulation center
near 0600 UTC on the 19th, and that the depression became
Dolly a little more than six hours later.
The tropical cyclone developed near or just south of a mid- to upper-level
anticyclone. In that environment, Dolly strengthened on the 19th and 20th
and moved toward the west-northwest (Table 1,
Fig. 1 [49K GIF])
at a speed that decreased from 15 knots to about 8 knots.
Convection became better organized near the circulation center on
the 20th and, just before making landfall on the Yucatan peninsula
to the northeast of Chetumal, Dolly became a hurricane.
It weakened back to a tropical depression and slowed to about 5 knots
during its 24-hour passage over the peninsula, and satellite
pictures showed the center of cloud rotation displaced to the south
of the estimated surface circulation center.
Gradual restrengthening began a few hours after the surface center
arrived over the Bay of Campeche. Dolly regained hurricane status
and was at it strongest, with 70 knot winds and a
central pressure of 989 mb, when it accelerated to 15 knots and made its final
landfall about midway between Tuxpan and Tampico near 1800 UTC on
Dolly then weakened and, as a tropical depression, crossed central
Mexico. It continued to generate areas of deep convection and,
likely, heavy precipitation even while its surface center dissipated over the
eastern North Pacific Ocean
on the 25th.
b. Meteorological Statistics
The "best track"
(Table 1) was obtained from the data presented in
Figs. 2 (32K GIF) and
3 (39K GIF), and in Table 2.
Those figures show Dolly's estimated central pressure
and maximum one-minute wind speed, respectively, versus time. Position and intensity
estimates from satellite pictures were provided by the
Synoptic Analysis Branch (SAB) and
Tropical Analysis and Forecast Branch (TAFB),
and by the
Air Force Global Weather Central (AFGWC).
This information was supplemented by reconnaissance aircraft data provided by the
U.S. Air Force Reserves,
and surface observations from land sites and ships.
The only available official observations of at least tropical storm
force winds from a surface land site came from Tampico, Mexico.
There, 10-minute winds of 40 knots with gusts to 60 knots occurred
at 1045 UTC and 1145 UTC on the 23rd. An amateur radio report of
a gust to 59 knots was received from Tampico.
Ship reports of 34 knot or higher wind speeds are listed in
The three largest 24-hour rainfall totals reported to the
meteorological service of Mexico
came from Micos (12.94 inches), Santa Rosa (10.59 inches), and Puerto de Valles (10.00 inches).
The rains, which in some cases were heavier on Mexico's west coast
than its east coast, also occurred in the more widely-known cities
of Acapulco (7.48 inches), Los Mochis (7.06), Tuxpan (5.88 inches),
Chetumal(5.73 inches), Monterrey (4.93 inches), and Cancun (1.35 inches).
c. Casualty and Damage Statistics
According to newspapers reports, Hurricane Dolly was responsible
for fourteen deaths in Mexico--including six in Veracruz (all
drowned), three in Nuevo Leon, and one each in Pueblo Viejo and
Monterrey. Two people were missing in Nuevo Leon.
Those reports also indicated hundreds of residences destroyed and
35,000 people displaced. Severe damage occurred in Tuxpan,
Tamiahua, Pueblo Viejo, Platon, Panuco, Tampico Alto and elsewhere
along the coast of northeast Mexico. A river overflowed its banks
causing damage in Pueblo Viejo. A large area of farm land was lost
to flooding in Quintana Roo on the Yucatan peninsula.
Rain prompted evacuations in the southern part of the state of San
Luis Potosi. About 6500 people were evacuated from low-lying zones
Widespread communication and power outages were noted as far
west as Mazatlan.
d. Forecast and Warning Critique
Table 3 provides track forecast error statistics.
The cyclone was relatively short-lived and only five forecasts through 72 hours
could be evaluated. The best model performance was made by BAMD
which had astonishingly small errors (e.g., average error of 31 nm
at 72 hours). The NHC average track forecast errors were not as
small as those of the BAMD, but were much smaller than the those of the
VBAR, and the interpolated GFDI and UKMI guidance. The
NHC errors were smaller than the most recent 10-year average, as
well. Most NHC intensity forecast errors were 15 knots or less.
Table 4 lists tropical storm and hurricane watches
and warnings issued by the government of Mexico.
Table 4. Tropical Cyclone watch and warning summary, Hurricane Dolly
||Tropical Storm Warning issued
||Chetumal to Progreso, Mexico|
|Tropical Storm Watch issued
||Pinar del Rio Province and Isle of Pines, Cuba|
|19/2100||Tropical Storm Warning issued
||San Pedro, Belize to Mexico border|
|20/1200||Tropical Storm Watch discontinued
|20/1500||Tropical Storm Warning issued
||Progreso to Ciudad del Carmen|
||Hurricane Warning issued--replaced
Tropical Storm Warning
||Cozumel to Chetumal|
||Hurricane Warning and Tropical Storm Warning discontinued
||South of Cozumel|
|21/0300||Tropical Storm Warning discontinued
||eastward from 88W|
|21/0900||Tropical Storm Warning discontinued
||east of Progreso|
|21/1500||Tropical Storm Warning discontinued
||remainder of Mexico|
|22/0900||Hurricane Watch issued
||Veracruz to La Pesca, Mexico|
||Hurricane Warning issued-replaced
||Veracruz to La Pesca|
||Hurricane Warning discontinued||Veracruz to La Pesca|