Tropical Cyclone Report
21 - 28 July 2001
Miles B. Lawrence
National Hurricane Center
13 August 2001
Dalila moved along the Pacific coast of Mexico for several days,
but its center remained 100 n mi offshore. Dalila briefly reached
hurricane strength. Some flash flooding in the province of Chiapas
is attributed to Dalila's rainfall.
a. Synoptic history
Dalila's origin is a tropical wave that moved westward from
Africa and over the eastern tropical Atlantic Ocean on 10 July. It
crossed northern South America and Central America on the
15th through 17th accompanied by vigorous
thunderstorm activity, and then entered the Pacific basin on the
18th as an organized area of disturbed weather.
Early on the 21st, the system acquired a low-level
circulation and became Tropical Depression Five-E, about 250 n mi
south of the Gulf of Tehuantepec. Moving west-northwestward, it
became Tropical Storm Dalila with 35-kt winds 12 hours later. The
track of Dalila is plotted in
Figure 1, and Table 1 lists the best
track six-hour positions, maximum one-minute wind speed, and
minimum central surface pressure.
Dalila's track was toward the west-northwest at forward speeds
between 5 and 15 kt. The direction of motion was rather steady,
varying between 285 and 300 degrees heading. This is attributed to
a persistent subtropical ridge of high pressure located north of
the cyclone. The center reached its point of closest approach to
the coast of Mexico between Acapulco and Manzanillo on the
22nd and 23rd, when it came within about 100
n mi of the coast.
With warm sea surface temperatures and minimal vertical shear,
the winds increased from 35 to 60 kt between the 22nd
and 23rd. The wind speed briefly reached
an estimated 65 kt on the
24th. Dalila was a hurricane for only a few hours and
then remained at 55 kt until early on the 27th. The
storm passed directly over Socorro Island on the 25th.
By the 27th, most of the associated deep convection
dissipated as the storm moved over colder water. Reduced to a swirl
of low clouds, Dalila dissipated as a tropical cyclone on the
28th, while located about 650 n mi west of the southern
tip of Baja California.
b. Meteorological statistics
All of the observations used to track Dalila and to determine
its wind speed and pressure were satellite-based. The observations
are plotted in
Figure 2 and Figure 3,
which also show the best track wind
and pressure curves.
The best track peak intensity of 65 kt at 1200 UTC on the
24th is plotted in Figure 2, and listed in
Table 1. Dvorak
intensity estimates during this time were as high as 77 kt. These
estimates were based on night-time infrared images which showed a
cold central dense overcast (CDO) clould pattern located over what
was presumed to be an embedded center.
In contrast to the Dvorak technique, SSM/I and TRMM passes show
a low-level center partially exposed to the northeast of the CDO,
rather then embedded within. Visible images several hours later
also do not support an embedded center. Intensity (pressure)
estimates from the Advanced Microwave Sounding System (AMSU) (Not
plotted in Figure 3) give a lowest pressure of 992 mb on the
c. Casualty and damage statistics
An Associated Press report stated that heavy rains associated
with Dalila caused flash flooding that damaged dozens of homes on
the Chiapas coast.
d. Forecast and warning critique
Official track errors are very small, increasing from 30 n mi at
12 hours to 120 n mi at 72 hours for 11 cases. The average official
72-hour error is 185 n mi for the previous 10 years. Intensity
errors range from 4 kt at 12 hours up to 17 knots at 48 hours, then
decrease to 15 knots at 72 hours. These errors are also below the
previous 10-year averages (18 kt at 48 hours and 21 kt at 72
Because of Dalila's rather close approach to the coast, the
Government of Mexico issued various watches and warnings. These are
listed in Table 2.
Table 1: Best track for Hurricane Dalila, 21 - 28 July 2001.
|Lat. (°N)||Lon. (°W)
|21 / 0000||11.3||93.8||1007||30||tropical depression
|21 / 0600||11.9||94.9||1006||30||"
|21 / 1200||12.4||96.0||1004||35||tropical storm
|21 / 1800||13.0||97.0||1001||40||"
|22 / 0000||13.6||98.2||997||50||"
|22 / 0600||14.2||99.4||994||55||"
|22 / 1200||14.8||100.7||994||55||"
|22 / 1800||15.5||102.1||994||55||"
|23 / 0000||16.1||103.4||994||55||"
|23 / 0600||16.7||104.5||994||55||"
|23 / 1200||17.2||105.6||994||55||"
|23 / 1800||17.5||106.4||994||55||"
|24 / 0000||17.7||107.3||990||60||"
|24 / 0600||18.0||108.1||988||60||"
|24 / 1200||18.2||109.0||987||65||hurricane
|24 / 1800||18.4||109.8||988||60||tropical storm
|25 / 0000||18.6||110.5||989||60||"
|25 / 0600||18.8||111.1||990||55||"
|25 / 1200||19.0||111.6||990||55||"
|25 / 1800||19.1||112.2||990||55||"
|26 / 0000||19.3||112.8||990||55||"
|26 / 0600||19.5||113.4||990||55||"
|26 / 1200||19.7||114.0||990||55||"
|26 / 1800||19.9||114.7||990||55||"
|27 / 0000||20.1||115.5||990||55||"
|27 / 0600||20.4||116.3||992||50||"
|27 / 1200||20.7||117.1||994||45||"
|27 / 1800||21.1||117.9||996||40||"
|28 / 0000||21.5||118.9||999||35||"
|28 / 0600||22.0||119.9||1003||30||tropical depression
|28 / 1200||22.4||121.1||1007||25||"
|28 / 1800||dissipated
|24 / 1200||18.2||109.0||982||65||minimum pressure
Table 2: Watch and warning summary, Hurricane Dalila, 21 - 28 July 2001.
|21/1500||tropical storm watch||Puerto Angel to Acapulco
|22/0300||tropical storm warning||Punta Maldonado to Lazaro Cardenas
|22/0300||hurricane watch||west of Lazaro Cardenas to Manzanillo
|22/0300||tropical storm watch discontinued||east of Punta Maldonado
|22/0900||tropical storm warning and hurricane watch
|22/0900||tropical storm warning||extended from Punta Maldonado to Punta San
|23/0300||all watches and warnings discontinued||
Best track map for Hurricane Dalila, 21-28 July 2001.
Best track maximum 1-min surface wind speed curve for Hurricane Dalila,
21-28 July 2001.
Best track minimum surface pressure curve for Hurricane Dalila, 21-28 July