African Easterly Wave Evolution Pre- and Post-tropical Cyclogenesis

The evolution of African Easterly Waves (AEWs) up until the time of tropical cyclogenesis has been given significant attention. However, the transition from tropical wave to a tropical cyclone has received relatively less attention. Many numerical simulations begin with a vortex to initiate tropical formation. As a result, few of these modeling studies examine how this wave and incipient vortex interact during tropical cyclogenesis. The purpose of the current study is to examine the fate of AEWs leading to tropical cyclogenesis and the process of wave-tropical cyclone decoupling. This will provide tropical meteorologists with a better understanding of the role of the wave in the actual process of tropical cyclogenesis.

The primary dataset utilized in this study is GFS reanalysis data. Based on this observational study, three types of fates of AEWs involved in tropical cyclogenesis are observed. The waves leading to “type A” storms quickly become wrapped up in the vortex. “Type B” waves split during the processes of tropical cyclogenesis. Part of the wave becomes wrapped up in the tropical cyclone's circulation, while the remaining part continues propagating to the west following the wave packet phase speed. A third “type C” case is a hybrid case. The wave neither becomes wrapped up or splits from the mean tropical circulation. Rather, it continues propagating within the tropical cyclone, retaining its wavelike characteristics.

One storm from each of these types of AEW fates are then initialized into the Weather Research and Forecasting Model (WRF). This modeling study aid in better understanding of the dynamics of the wrap-up, splitting, and hybrid cases.