Observational Analysis on the Evolution Features of Severe Convective Rainbands of the Torrential Heavy Rain Producing Typhoon Rumbia (2018)

In August 2018, Typhoon Rumbia made landfall in Zhejiang Province, China. It brought extremely heavy rainfall to Jiangsu, Anhui, Henan, Shandong and Liaoning provinces. The most extremely heavy rainfalls were located around the boundaries among Anhui, Henan and Shandong provinces, with the maximum daily rainfall of 505.6 mm recorded in Henan Province. Based on intensive surface and radar observations and NCEP reanalysis data as well as the best track data from Shanghai Typhoon Institute, this work examines the structure and evolution of the rain bands of Typhoon Rumbia that caused torrential heavy rain in East China. The results showed that the rain bands twice manifested evolutions from multiple short rain bands into a single long rain band respectively in the two torrential heavy rainfall areas. In the inverted trough area of the tropical cyclone, multiple short rain bands first produced wide area of rainfall. Then with the increase of the convergence between the southwesterly flow on the east side of the tropical cyclone circulation and the southeasterly wind on the west side of the subtropical high, a long quasi-stationary rain band formed with apparent back-building features. Wth the intensification of low-level vertical wind shear, the rain bands displayed apparent convective features with embedded bow echo, supercell, and even tornadoes. The environmental features that favored the evolution of those convective rainfall bands were examined. Results showed that the maintenance and evolution of the rain bands were determined mainly by the sustaining of typhoon circulation and intensity and its interaction with the stagnation and westward extension of subtropical high.