a. Synoptic History
Satellite imagery showed an area of cyclonic circulation associated
with a tropical wave over west-central Africa on 19 July. The system moved
westward and it was clearly observed as a distinct mid-level cloud rotation south
of the Cape Verde Islands on 22 July. Thereafter, the wave became less distinct
but it continued westward and crossed Central America during 31 July. Convection
then began to increase but it was not until 4 August that the cloud pattern showed
some organization and satellite classifications began. Based on ship reports and
satellite it is estimated that the system became a tropical depression
at 1200 UTC 6 August when it was located about 480 n mi south of the southern tip of Baja
The depression moved on a general northward track, apparently
steered by the flow around a mid-level trough just west of the U.S. west coast and
a high over Mexico. The depression reached tropical storm status at 0000 UTC 8
August and became a threat to portions of Baja California. Frank's maximum
intensity was estimated at 40 knots with a minimum
pressure of 1001 mb at 0000 UTC on the 9th. Frank turned toward the north-northwest,
which maintained a portion its the circulation over Baja California. It
reached cooler waters and gradually weakened.
Frank's track is shown in Fig. 1 (22K GIF).
Table 1 is a listing, at six-hourly 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 are
shown in Figs. 2 (15K GIF) and
3 (16K GIF) and are based on satellite intensity
estimates from the Tropical Analysis and Forecast Branch (TAFB),
Analysis Branch (SAB) and the Air Force Weather Agency,
(AFGWC) in figures. Winds of 30-35 knots reported by the ship C6LF9
were used to upgrade the tropical depression to tropical storm status. As Frank approached Cabo
San Lucas, the system was under surveillance by Mexican radar at that location.
This was very helpful in locating the center of the storm and the rainbands.
c. Casualty and Damage Statistics
There were no reports of casualties or damage associated with
Frank. Bands of heavy showers and gusty winds were observed primarily in the Gulf
of California and moisture from the storm reached the southwestern U.S.
d. Forecast and Warning Critique
Since Frank was a threat to Baja California,
tropical storm watches and
warnings were required for a portion of this area.
Frank was a tropical storm for less than two days. Therefore, an
evaluation of the average forecast errors would not be meaningful. However, it is
important to note that initially, with the exception of NOGAPS, track models did
not forecast the northward motion of the storm. Instead, track models turned Frank
toward the northwest and west-northwest. The official forecast was nearly always
to the right of most of the guidance.
Table 2. Tropical Cyclone watch and warning summary for Baja California, Tropical Storm Frank.
|7/2100||Tropical Storm Watch issued
||South of Cabo San Lazaro and south of Los Burros|
|8/0900||Tropical Storm Warning issued
||Cabo San Lazaro to Punta Abreojos|
|Tropical Storm Watch issued||north of Punta Abreojos to Punta Eugenia|
|Tropical Storm Watch discontinued
||South of Los Burros and south of Cabo San Lazaro|
|8/1200||Tropical Storm Warning extended southward
||Punta Eugenia to Punta Tosca|
|9/0900||Tropical Storm warnings discontinued
||Punta Eugenia to Punta Tosca |