Analysis of an Unusually Heavy,Flood-Causing Rain at Gaotan,Huizhou

Using the 0. 5 × 0. 5 gridpoint data of CFSR and records from automatic watch stations from August 16- 17,2013,this work studies an unusually heavy,flood-causing rain that took place in the town of Gaotan,Huidong county,Huizhou city. The results are shown as follows. Typhoon Utor left behind a pattern of circulation that stagnated and maintained for extended time,constantly supplying( generally) southerly flows to Gaotan and its adjacent area to feed the zone of heavy rain with abundant amount of warm and humid water vapor. A southwesterly converged with a southerly to form mesoscale fronts of energy and dew point that helped the heavy rain to generate and develop. During the rain,there were unstable stratification and intense ascending motion as well as a favorable allocation of low-level convergence and upper-level divergence in the region. Besides,a counterclockwise rotating vertical wind field was also present in the zone of heavy rain and the area to its west. The local U-shaped and trumpet-shaped terrain as well as near-surface convergence of a surface wind field played an essential role in enhancing the rain in the studied region.