Tropical Cyclone Report

Tropical Storm Genevieve

Tropical Storm Genevieve formed south of Baja California and soon moved over cool waters.

a. Synoptic History

A tropical wave crossed Dakar, Senegal on 13 August. The wave was accompanied by a large area of thunderstorms with a well-defined low-level cyclonic wind-shift and a column of high moisture that extended from the surface to near 400 mb. As the wave moved westward, it lost most of its associated convection, and it was not until the system was south of Hispaniola on the 19^th that the thunderstorm activity partially regenerated. Thereafter, the wave continued westward with a gradual increase in organization and crossed Central America where developed a distinct mid-level circulation. A tropical depression formed at 0000 UTC 26 August about 500 n mi south of the southern tip of Baja California and became a tropical storm 24 hours later. Genevieve was near hurricane strength with maximum winds of 60 knots and a minimum pressure of 989 mb at 0000 UTC 28 August when it turned to the northwest toward cooler waters and convection began to weaken. It was dissipating about 960 n mi west-northwest of the southern tip of Baja California at 0600 UTC 1 September. A swirl of low clouds associated with Genevieve's remnants persisted for a couple of days.

The "best track" chart of Genevieve's path is given in Figure 1 with the wind and pressure histories shown in Figure 2 and Figure 3, respectively. The best track positions and intensities are listed in Table 1.

a. Meteorological Statistics

Observations in Genevieve (Figure 2 and Figure 3) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), the Satellite Analysis Branch (SAB) and the U. S. Air Force Weather Agency (AFWA). Infrared satellite estimates from TAFB and SAB indicated that Genevieve was a hurricane by 1200 UTC 28 August. However, visible satellite images a couple of hours later showed a disrupted cloud pattern indicating that the T-numbers were overestimated and Genevieve was not a hurricane.

c. Casualty and Damage Statistics

There were no reports of damage or casualties associated with Genevieve.

d. Forecast and Warning Critique

Average official track errors (with the number of cases in parentheses) for Genevieve were 36 (12), 63 (10), 74 (8), 85 (6), and 142 (2) n mi for the 12, 24, 36, 48, and 72 h forecasts, respectively. With the exception of the 12 and 24 hour periods, these errors are much lower than the average official track errors for the 10-yr period 1992-2001 of 36, 67, 97, 125, and 182 n mi, respectively). However, several of the numerical track guidance produced even lower errors than the official forecast at all times as indicated in Table 2.

Average official intensity errors were 7, 15, 17, 22, and 30 kt for the 12, 24, 36, 48, and 72 h forecasts, respectively. For comparison, the average official intensity errors over the 10-yr period 1992-2001 are 7, 12, 16, 18, and 21 kt, respectively.

Figure 1: Best track positions for Tropical Storm Genevieve, 26 August- 1 September, 2002.

Figure 2: Selected wind observations and best track maximum sustained surface wind speed curve for Tropical Storm Genevieve, 26 August- 1 September, 2002.

Figure 3: Selected pressure observations and best track minimum central pressure curve for Tropical Storm Genevieve, 26 August-1 September, 2002.