Water Vapor Budget in a Developing Tropical Cyclone and Its Implication to Tropical Cyclone Formation

The water vapor budget has not been well studied for a developing tropical cyclone at the pre-genesis stage. In this study, a high-resolution numerical model simulation of Tropical Storm Fay (2008) is used to examine the water vapor budget and respective changes in the overall moisture contribution before and after genesis in the marsupial framework. Analysis shows that the vertically integrated inward moisture flux accounts for a majority of the total condensation (especially for small radii) and its fractional contribution increases from the tropical wave to the tropical cyclone stage, while the fractional contribution of local evaporation is much smaller and decreases from the tropical wave to the tropical cyclone stage, suggesting the importance of the positive feedback between the primary circulation and the secondary circulation to tropical cyclone development. It was also shown that the radial moisture flux above the PBL is rather weak prior to genesis but increases significantly after genesis due to the deepening of the inflow layer.