Rapid Intensity Change in Hurricane Lili (2002)

Hurricane Lili (2002) developed in the western Caribbean Sea and intensified rapidly from a Category 2 to a Category 4 hurricane within 18 hr in the Gulf of Mexico and rapidly weakened to a Category 1 storm before making landfall at the Gulf coast. Lili intensified in the wake of Hurricane Isidore (2002) when the SST was relatively cooler than its “normal” conditions. The internal dynamics, i.e., the eye and eyewall structure may have played an important role in the rapid intensification in Lili. It was observed that Lili had a relatively small eye when it reached the maximum intensity. Most major hurricanes intensify as the eye and eyewall contract. However, some maintain a relatively larger eye than others. The question is what determines how far an eye can contract and how rapidly a storm can intensify? In the case of Hurricane Lili, the vertical wind shear asscociated with a through of the Texas/Lousiane coast prevented further intensification of the storm and played an important part in the rapid weakening of the storm. In this study, we use a high-resolution model to investigate some aspects of the physical processes responsible for the rapid contraction/intensification of Hurricane Lili (2002) and the following weakening. Based on the current analysis and previous studies from Schubert and Hack (1982), we hypothesize that the conversion from heating to warming at the edge of the eye-eyewall region, is particularly efficient. The model simulation shows that during the intensification stage the warming in the eye expands vertically from the lower levels (about 3km height) to the upper levels (about 15 km height) and reaches 3°C throughout this entire column in 18 hours. As showed by Shapiro and Willoughby 1982, this warming will cause the isobaric surface to fall rapidly (slowly) inside (outside) the radius of maximum winds (RMW). The largest gradient of isobaric height fall will be located inside of the RMW and supported a peak of the tangential wind tendency. The maximum of tangential wind propagates inward in response to warming in the eye. During Lili's weakening phase the vertical wind shear is shown to create asymmetries in the storm and to dissipate the warm temperature anomaly in the eye. Budget analyses of key dynamic and thermodynamic variables are currently underway to understand the sequence of events involved in the rapid intensification and weakening of Hurricane Lili (2002).