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Preliminary Report
Tropical Storm Frank
29 July - 8 August 1998

Lixion A. Avila
National Hurricane Center
1 October 1998

Tropical Storm Agatha
Hurricane Blas
Tropical Storm Celia
Hurricane Darby
Hurricane Estelle
Tropical Storm Frank
Hurricane Georgette
Hurricane Howard
Hurricane Isis
Tropical Storm Javier
Hurricane Kay
Hurricane Lester
Hurricane Madeline

[1998 East Pacific Hurricane Season]

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 California.

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), the Satellite 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. (Table 2).

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 1. Best track, Tropical Storm Frank, 6- 10 August, 1998.
Position Pressure
Wind Speed
Lat. (°N)Lon. (°W)
6/120016.7111.5100930tropical depression
8/000021.3112.1100535tropical storm
120027.1114.9100630tropical depression
9/000025.4113.3100140minimum pressure

Table 2. Tropical Cyclone watch and warning summary for Baja California, Tropical Storm Frank.
7/2100Tropical Storm Watch issued South of Cabo San Lazaro and south of Los Burros
8/0900Tropical Storm Warning issued Cabo San Lazaro to Punta Abreojos
Tropical Storm Watch issuednorth of Punta Abreojos to Punta Eugenia
Tropical Storm Watch discontinued South of Los Burros and south of Cabo San Lazaro
8/1200Tropical Storm Warning extended southward Punta Eugenia to Punta Tosca
9/0900Tropical Storm warnings discontinued Punta Eugenia to Punta Tosca

Jack Beven

Last updated May 21, 1999