Preliminary Report
Tropical Storm Isaac
28 September - 01 October 1988

1988 PRELIMINARY REPORTS

Tropical Storm Alberto (TS)
Tropical Storm Beryl (TS)
Tropical Storm Chris (TS)
Hurricane Debby (1)
Tropical Storm Ernesto (TS)
Hurricane Florence (1)
Hurricane Gilbert (5)
Hurricane Helene (4)
Tropical Storm Isaac (TS)
Hurricane Joan (4)
Tropical Storm Keith

a. Synoptic History

Tropical Storm Isaac can be traced back to a weak disturbance that was near the west coast of Africa on 23 September. This low latitude disturbance quickly merged with the intertropical convergence zone and moved westward in an undistinguished manner. On the 27th, satellite imagery showed a concentration and organization of convective activity in the mid Atlantic. On the 29th, the system was identified as Tropical Depression Sixteen while centered about 900 nautical miles east southeast of of Barbados, based on an interpretation of satellite imagery.

Depression Sixteen moved westward at 16 mph. On the 30th, it shifted two degrees of latitude northward, possibly as a result of the formation of a new center. It then continued continued westward, crossing through the southern Lesser Antilles and into the southeastern Caribbean on 1 and 2 October. Also, its forward speed increased to 21 mph during this period.

Satellite imagery showed that the low level cloud circulation center was exposed to the west of the deep convection on the 29th and early 30th, indicating a westerly vertical shearing of the horizontal wind. However, late on the 30th, an Air Force plane measured a 1500 feet wind speed of 59 mph to the north of the center and a central surface pressure of 1005 millibars and the depression was upgraded to Tropical Storm Isaac. The storm center was a little over 200 nautical miles east southeast of Barbados at this time and a tropical storm warning was issued for the islands of Barbados, the Grenadines, St. Vincent, St. Lucia, Dominica and Martinique at 2200 UTC on the 30th. Trinidad, Tobago, and Grenada and its dependencies were placed under a tropical storm watch at 0400 UTC on 1 October.

The intensification to tropical storm status didn't last long becasue of the shearing environment and Isaac was downgraded to a depression on the morning of the 1 October, while it was centered in the Windward Islands and less than 18 hours after it was named. The depression's circulation completely dissipated shortly thereafter.

b. Meteorological Statistics

The maximum 1-minute surface wind speed and the minimum surface pressure curves as a function of time are shown in Figures 2 and 3, along with the observations on which these are based. The short time that Isaac's surface winds were 39 mph or higher is reflected in the sharpness of the peak curve. The maximum 1-minute surface wind speed during Isaac's existance is estimated to be 46 mph, which is 80% of the highest aircraft flight level wind. The National Hurricane Center (NHC) satellite wind speed estimates appear to have a slight positive bias. That is, the center passed about 60 nautical miles south of Barbados at the time of the 0600 UTC. NHC satellite wind speed of 52 mph and barbados' surface winds were only 12 mph at the time.

c. Casualty and Damage Statistics

There were no reports of casualties or damage.