Abstract:The heavy rainstorm resulting from depression circulation of typhoon Meranti is studied with the analysis of Doppler radar reflectivity, mesoscale observational data and the diagnosis of the simulation results from the mesoscale numerical weather research and forecasting model (WRF). The main results show that the remained cloud system of Meranti, the warm and moist flows in the border of subtropical high and the weaker cold air from higher altitudes are responsible for this rainstorm. The precipitation radar reflectivity consists of cumulus and stratus, which can produce more precipitation amounts than a unique kind cloud. The interaction among several meso and micro scale convective systems is advantageous to the development of local convective cloud cluster, and the wind velocity zone occurs with the enhancement in the intensity and area of wind velocity. During the period of rainfall, the moist condition for precipitation is satisfied with the moist transporting into the rainfall region. The configuration of the vertical helicity at mid and low levels, the strong ascending movement resulting from the invasion of the weak cold air into the air column where the negative moist potential vorticity is at low levels and the positive moist potential vorticity is at middle and upper levels, and the heating effect coming from the latent heat release made a sustained pumping action, which leads to the standing raining and forms the rainstorm in Hangzhou. This can be an index for forecasting tropical cyclone local rainstorm.