Hurricane Isidore 1996

Preliminary Report
Hurricane Isidore
24 September - 02 October 1996


Tropical Storm Arthur (TS)
Hurricane Bertha (3)
Hurricane Cesar (1)
Hurricane Dolly (1)
Hurricane Edouard (4)
Hurricane Fran (3)
Tropical Storm Gustav (TS)
Hurricane Hortense (4)
Hurricane Isidore (3)
Tropical Storm Josephine (TS)
Tropical Storm Kyle (TS)
Hurricane Lili (3)
Hurricane Marco (1)

a. Synoptic History

Hurricane Isidore formed from a tropical wave that had a well-defined cyclonic circulation of clouds and was clearly marked at mid-levels in the Dakar sounding data when it crossed the west coast of Africa on 22 September 1996. Deep convection increased and satellite analysts provided the first Dvorak scale T-numbers on the 23rd, while the circulation passed to the south of the Cape Verde Islands. Thunderstorms became more concentrated, T-numbers from the NOAA Tropical Analysis and Forecast Branch (TAFB) increased to 2.0, and ship reports suggested the formation of a surface circulation by 1200 UTC on the 24th. The "best track" begins at that time, indicating the start of the tropical depression stage of Isidore.

The tropical cyclone was initially located to the south of a deep-layer anticyclone. It moved toward the west-northwest at 17-23 mph and intensified. An intense convective band wrapped around the center and the system became a tropical storm on the 25th. Further intensification ensued, an eye began to appear intermittently, and Isidore reached hurricane intensity on the following day.

The mature and dissipating stages of Isidore were influenced by a well-defined mid- through upper-level low that was quasi-stationary near 25°N 45-50°W through the 25th. The low then weakened and lifted northward to near 35°N, but was reinvigorated there by its interaction with a mid-latitude short-wave trough which passed by to the north on the 27-28th. The steering currents on the east side of the low gradually turned Isidore in a general northward direction. The forward speed slowed to about 12 mph during the turn on the 28th, but then increased to 23 mph on 1 October. During this period, Isidore reached its estimated maximum intensity of 115 mph winds. The eye disappeared on the 29th and upper-level westerly to southwesterly winds of around 69 mph contributed to a shearing and weakening of Isidore, down to a tropical storm with an exposed low-level cloud center on the 29th, and then to a tropical depression on the 1st. Deep convection dispersed and Isidore transformed to extratropical status on the 2nd.

b. Meteorological Statistics

The ship Magnific reported southeast (140°) winds of 67 mph at 1200 UTC on the 30th of September, while located at 25.1°N 37.2°W, about 175 nautical miles from the center of Isidore. The reliability of that measurement is in doubt because the estimated maximum surface wind near the center was 58 mph at that time. This was the only surface sustained wind report of 39 mph or higher to be possibly associated with Isidore.

c. Casualty and Damage Statistics

No reports of casualties or damages were received.

Maximum Intensity For Hurricane Isidore
24 September - 02 October, 1996

Position Pressure
Wind Speed
Lat. (°N) Lon. (°W)
28/0000 15.8 42.9 960 115 Category 3 Hurricane