Role of Intense Updrafts in Tropical Cyclone Formation

The role of intense updrafts (vertical velocity greater than 1 m s^-1) in tropical cyclone formation is examined in the cloud-resolving numerical model simulation of Tropical Storm Fay (2008). The simulation covers the tropical wave stage to the tropical storm stage. It was found that the intense updrafts, although occupying less than 5% of the area prior to genesis, make a significant contribution to net condensation and play an important role in moistening the middle troposphere. Intense vortices (with relative vorticity greater than 10^-3 s^-1), presumably associated with vortical hot towers, occupy about 5-10% of the area but account for 40-50% of the system-scale cyclonic vorticity. The development of tropical cyclone is characterized by amplification and more frequent occurrences of intense updrafts and intense vortices, which are modulated by diurnal cycle of tropical convection prior to genesis.