The highly asymmetric structure of Hurricane Earl (1998) near landfall

Tropical cyclones (TC) sometimes interact with mid-latitude troughs resulting in a "hybrid" structure not typical of a classic TC. This may cause the storm to have an extremely asymmetric wind field and have a satellite signature which can lead to an underestimate of the storm's intensity. One such TC, Hurricane Earl, made landfall near Panama City, FL as a category one system at 0600 UTC 3 September 1998. Dvorak estimates of Earl's intensity peaked in the 25 m/s range yet the minimum surface level pressure reached 985 mb, supporting a much higher wind speed than the satellite-based estimate. Observations from a NOAA P-3 research flight and Air Force reconnaissance missions showed a highly asymmetric wind field with wind speeds greater than hurricane force confined to a large rainband ~150 km east of the center. Radar observations from the NOAA aircraft also indicated an asymmetric structure with convection limited to rainbands north and east of the eye. A quasi-eyewall was also observed but flight-level (~3 km) winds indicated that the wind center was actually within the high-reflectivity region of the northern eyewall. This is suggestive of a sheared and tilted vortex with possible baroclinic influences. A combination of data from USAF reconnaissance sorties and A NOAA research flight, including airborne radar and GPS dropwindsondes are used to investigate the thermodynamic and kinematic fields of Hurricane Earl near landfall. A discussion of the hybrid structure of this TC will be presented.