Abstract: The No. 0814 Typhoon Hagupit was weakened to a cyclone as soon as it made a landfall in Caobang, Vietnam, at 8 am on September 25th, 2008. With the development of meso-scale convective clouds (MCCs) that were generated outside the cloud system of the cyclone, a destructive rainfall was triggered in southwestern Guangxi, even much heavier than the one caused by a typical tropical storm. Analysis of the United States National Center for Environmental Prediction (NCEP) data indicated that negative vorticity extended to the middle and bottom of the troposphere as a result of westward retreat of the South Asia High; as a result, the western Pacific subtropical high at 500 hPa became weaker and retreated toward east to be the background condition of the standstill and the development of convective clouds in southwestern Guangxi. Four MCCs that caused the rainfall were generated in 100 - 200 km range of the right side of the warm shear; in other words, they were to the north of the warm shear, and moved from southeast toward northwest. The precipitation field showed a southeast–northwest quasi-zonal rainfall distribution. Warm shear, vertical pumping effect, neutral wet character of the lines of θ _se high value formed in funnel shape, and the wet Q vector’s activation of the secondary circulation helped to strengthen the MCCs. The wet tongue and wet Q vector convergence zone were good reflections of the region and the time of latter heavy precipitation emergence.

Key words: Hagupit;warm shear;wet Q vector;neutral wet structure, mesoscale convective