The structure of Hurricane Irene over South Florida

On October 15, 1999, Hurricane Irene made landfall on the southwest coast of Florida, tracked to the northeast across the peninsula before emerging into the Atlantic Ocean north of Palm Beach. Irene was a Category 1 hurricane at landfall with maximum sustained surface winds estimated at 65 kts and a central pressure of ~ 982 mb. A NOAA WP-3D aircraft conducted a landfall research mission during the time Irene was crossing Florida. The aircraft, operated by the Aircraft Operations Center (AOC) and staffed by scientists from HRD, flew at an altitude of 8,000 feet and completed a flight track that provided coverage over the South Florida Peninsula and adjacent coastal waters in the Gulf of Mexico, Florida Bay, and Atlantic Ocean. In addition to the in-situ wind and thermodynamic measurements at flight-level, observations from the airborne Doppler tail radar, lower-fuselage radar, GPS dropsondes, and step-frequency microwave radiometer (SFMR, surface wind speeds) were collected by the AOC and HRD crew.

A detailed description of the wind and thermodynamic structure of Irene while over South Florida will be presented. Of particular interest is comparisons of flight-level wind measurements with surface observations from regular observing sites over land and from C-MAN and buoy measurements, and those from the GPS dropwindsondes and the SFMR. Satellite imagery showed that intense, deep convection was occurring over the center of Irene, obscuring the eye and eyewall that was visible on radar displays beneath the high clouds. An unusual aspect of Irene was the extremely dry air that was entraining into the west side of the storm and that may have contributed to some of the observed asymmetries and to the clear-air turbulence encountered by the P-3 aircraft.