Water Budget and Intensity Change of Tropical Cyclones over the Western North Pacific

Three satellite observational data sets and a reanalysis data set during the period 2001–2009 are used to examine four water budget components (total precipitable water, surface evaporation, precipitation, and column integrated moisture flux convergence) associated with western North Pacific tropical cyclones (TCs) of different intensity change categories: rapidly intensifying, slowly intensifying, neutral, and weakening. The results show that surface evaporation plays an important role in storm rapid intensification (RI) and the highest evaporation associated with rapidly intensifying TCs is associated with the highest sea surface temperature. Total precipitable water in the outer environment, where moisture is mainly provided by surface evaporation, is also vital to storm RI because RI is favored when there is less dry air intruded into the storm circulation. The roles of surface evaporation and total precipitable water in storm RI are related to the enhanced convective available potential energy by moistening and warming the boundary layer. The largest amount of column integrated moisture flux convergence associated with weakening TCs, which results in the heaviest precipitation, are because their strongest mean intensity promotes moisture transport. It is suggested that different water budget components play different roles in TC intensity change. The results agree with the notion that TC intensity change results from a competition between surface moisture and heat fluxes and low-entropy downdrafts into the boundary layer.