Warm core ocean features in the central and eastern Gulf of Mexico

A pair of NOAA P-3 research flights were made early in the 1999 North Atlantic hurricane season into the Gulf of Mexico. The goal of the flights was to determine the upper-ocean environment over which a tropical cyclone might pass later in the season. Prior to the mission, a combination of AVHRR SST analyses and altimetry data from TOPEX-POSEIDON and ERS showed anomalous positive sea-heights in the vicinity of the "loop current" west of the Florida peninsula, suggesting the presence of a deep warm water within the region. It is beleived that under the right conditions this "oceanic heat reservoir" can act to intensify tropical cyclones that move into the region. A total of 47 Airborne Expendable Bathythermograph (AXBT) profiles were made during the two NOAA flights. Area coverage was approximately a 5 deg X 5 deg region between 24-29 N latitude and 86-91 W longitude. AXBTs provide ocean temperature as function of time, and the depth is inferred assuming a constant fall rate. Profiles consistently reached a depth of at least 300 m. By assuming steady-state ocean conditions between flights over the two day period, the temperature data is interpolated objectively to a three-dimensional grid in order to assess the structure of the warm water pool, both horizontally and as a function of depth. Via graphical visualization of the gridded temperature data, two key features were noted: the existence of a strong upper ocean thermal gradient (front) along the western wall of the loop current (which was later validated by altimetry sea height anomaly data); as well as a "weakness" in the warm core structure itself, indicating that an eddy-like feature may have been in the process of "cutting off" from the main flow. While there have been no realizations of storms crossing the sampled region during the 1999 season, recent (October 1999) TOPEX-POSEIDON/ERS analyses have indicated the existence of a "cutoff eddy" located in the central Gulf. These data suggest that the "weakness" identified in the early season AXBT analyses may now be a distinct warm core eddy feature. A multi-dimensional graphical description of the region sampled will be presented.