Abstract:In this article, the non hydrostatic WRF V3.6.1 (Weather Research and Forecast) model is used to simulate Typhoon Chan Hom at high resolution with three nests. The model can well simulate the development and evolution of Typhoon Chan Hom as well as the precipitation that it brought to the northeast of Zhejiang. Observation data indicate that the topographic friction convergence and lifting under northeast air flow make the strong convective systems gather in the northwest of the typhoon eye in the vicinity of Zhejiang, with a lot of convective cloud cluster in the convective systems. This is an important reason for the record breaking rainfall in northeastern Zhejiang. The control simulation also captures these features. The precipitation system is consistent with orientation of topography, i.e. the rainfall increases on the windward side. The sensitivity experiments show that topography in the northeast area of Zhejiang plays an important role in the increment of the typhoon rainfall. By lowering the terrain, the small scale convective systems get reduced apparently. Meanwhile, the rainfall in northeastern Zhejiang weakens as well. Thus, topography can impact the structure and evolution of these convective systems, causing the abnormal changes of precipitation. Of more importance is that Typhoon Chan Hom maintained the highly symmetric structure in the vicinity of Zhejiang, with the typical eyewall and warm core structure.