An Observational Study of Hurricane Georges (1998) as a Mature Tropical Cyclone

An observational study of Hurricane Georges (1998) is carried out using dropsondes and in situ flight-level data collected during its peak intensity in the north Atlantic. There were four reconnaissance missions flown into the storm that covered a 15-h period while it was a strong Category 4 tropical cyclone. The dropsonde analysis reveals that the peak azimuthally-averaged storm-relative tangential wind speed occurs persistently within the boundary layer and indicates significant supergradient winds are prevalent near and just within the radius of maximum tangential winds. Additionally, all 18 eyewall dropsondes indicated that the maximum tangential wind speed is located within the boundary layer. The gradient wind analysis is at odds with a previously peer-reviewed article on Hurricane Georges, which concluded there were no significant supergradient winds present in the storm. The findings in this study lend additional credence to a recent theory on the tropical cyclone intensification process from a system-scale framework, where the peak tangential wind is located within the boundary layer and then becomes supergradient prior to the air ascending into the eyewall updraft. In addition, these results are similar to newly published observations from Supertyphoon Jangmi (2008) and Hurricane Earl (2010).