Study on the climatic characteristics and classification of regional rainstorms caused by weakened tropical cyclones

By using objective separation method and its improved extraction algorithm, tropical cyclone precipitation is obtained. Based on tropical cyclones from 1965 to 2013, which caused rainstorms within 24 hours of TC weakening, research is carried out on the climatic characteristics and their corresponding classification of regional rainstorms. Results show that eastern Guangxi, Guangdong and southern Fujian are the main distribution areas of regional rainstorms within 24 hours of TC weakening (WTCR₂₄). WTCR₂₄ frequency has a slowly decreasing trend in the past 49 years and the frequency of WTCR₂₄ is correlated to the frequency of TC. In the three types of circulation patterns, i.e., high pressure dam in the North, the saddle, incorporated into the upper trough, whether TC crosses the subtropical high line and whether subtropical high is weakened are the key turning points for precipitation forecast. The weakening TC incorporated into the stronger TC circulation is the key to WTCR₂₄ for double-typhoon type.