EFFECTS OF SST, VWS, AND DCC UPON RAPID INTENSIFICATION OF OFF-SHORE TYPHOONS IN CHINA SEAS

In this study, we employed National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data and records from the China Meteorological Administration (CMA) Yearbook of Tropical Cyclones to investigate three factors: sea-surface temperature (SST), vertical wind shear (VWS), and the density of the core convection (DCC), which are responsible for the rapid intensification (RI) of 1949-2013 offshore typhoons. Our analysis results of these composite factors show that in the environmental wind field the typhoons are far away from the outer strong VWS; in the SST field they are in the high SST area; and the core convective activity is robust and takes a bimodal pattern. The difference in RI between typhoons over the East China Sea (ECS) and the South China Sea (SCS) is a smaller VWS for the ECS typhoons, which may be one of the reasons why typhoons in the ECS are more intense than those in the SCS. Our study results indicate that SST, VWS, and DCC can result in an RI after a certain time interval of 36 h, 24 h to 30 h, and 24 h, respectively. The RI indicates a lag in the atmospheric response to oceanic conditions. This lag characteristic makes it possible to predict RI events. In summary, where the SST is high (≤28 °C), the VWS is small, and the DCC is high, an RI will occur. Where mid-range SSTs occur (26≥"SST"28≥), with small VWS, and high DCC, the RI of typhoons is also likely to occur.