Hurricane Isabel became a powerful category five storm on the Saffir-Simpson scale on September 11th, 2003 and maintained this intensity over a four day period. The NOAA Hurricane Hunters flew multiple missions into Isabel from September 11th to September 14th, collecting a multi-platform dataset that includes dropsonde, step-frequency radiometer, lower-fuselage surveillance radar and tail Doppler radar data, in situ measurements, and video footage. High-resolution rapid scan satellite imagery was also recorded during this time period. These instruments show several unique features, including the presence of extremely high wind speeds, multiple mesovortices, and a polygonal eyewall.

This paper will present a composite view of Isabel at maximum intensity from these multiple data sources, and will explore the thermodynamic and azimuthal mean wind structure of the vortex derived from the in situ, dropsonde and Doppler measurements. A preliminary two-dimensional stability analysis of the vortex structure has been performed using the flight-level winds indicating potential growth of higher-order wavenumber instabilities, and will be compared with the observed polygonal eyewall and mesovortex structure. The diagnosed thermodynamic structure is consistent with previous hurricane studies, and the mechanisms that may have contributed to the unusually high wind speeds and possible "superintensity" of Isabel during this time period will be discussed.