Characterizing and Understanding Tropical Cyclone Intensification Using HWRF Ensemble Data Assimilation System (HEDAS) Dataset

Environmental vertical wind shear (VWS) has long been recognized as a major inhibiting factor for tropical cyclone (TC) intensification. Yet, TCs do develop or even undergo rapid intensification (RI) in light to moderate VWS. It is still not fully understood how TC internal dynamical processes and energetics overcome the detrimental effect of VWS and lead to the TC intensification. In this study, we aim to understand the mechanisms underlying TC intensification in shear using the data generated by the Hurricane Weather Research and Forecast (HWRF) Ensemble Data Assimilation System (HEDAS). HEDAS comprises a version of HWRF and an ensemble Kalman filter with the capability of assimilating storm-relative observations, such as the dropsondes, flight-level measurements, tail Doppler radar data, etc., in the system. We classified the TCs in the HEDAS dataset in terms of different storm intensities and different environmental moisture and shear conditions and analyzed the data in the moist static energy (MSE) framework. The preliminary results show that the vertically integrated mass-weighted MSE (WMSE) exhibits a somewhat increasing trend with the storm intensity during the storm intensification period. The signal is particularly robust for major hurricanes and TS&TD, less apparent for a weak storm. No relationship between WMSE and storm intensity is found once a storm reaches its peak intensity. The results suggest the unique energetic processes underlying the rapid intensification of major TCs.