Role of the Upper Ocean Structure on the Intensification of Hurricane Bret From Satellite Altimetry

During 18-24 August 1999 hurricane Bret intensified twice when its path crossed over two warm rings in the southwestern Gulf of Mexico which were shed by the Loop Current several months earlier. Warm anticyclonic rings such as the ones found during this episode are characterized by larger sea height than their surrounding waters. Satellite altimetry, which measures the sea height anomaly in the ocean and a two-layer reduced gravity ocean model are used to to track these rings and study their physical properties. A recently developed methodology allows to estimate the depth of the main thermocline and of the 26° C isotherm from altimeter data. This information, along with the climatological shape of the vertical ocean temperature profiles is used to estimate the hurricane heat potential. This parameter is proportional to the integrated vertical temperature in the ocean from the surface to the depth of the 26° C isotherm, and is an index of the thermal energy available in the upper ocean that can be transferred to a tropical cyclone. Initial results suggest that the altimeter-derived hurricane heat potential of these two rings exceeded 90 KJ cm^-2. These results are compared against AXBT-derived estimates as well as prestorm measurements from AXCTDs and AXCPs over the central Gulf of Mexico in the Loop Current.