A Study on Sudden Intensification of Typhoon Sam at Hongkong coast area

Tropical cyclone 9908 (SAM) formed in evening of 19th August 1999. It intensified as a tropical cyclone at afternoon 20th August. It moves into South China Sea and moves to the northwest continually in the evening. It developed as the intensity of a typhoon at morning 22th.Typhoon SAM was landing in Hongkong and Shenzhenat area at 5:30 (Beijing time) 22th.

In this paper, an observed study on typhoon SAM (9908), which was landing in Hongkong and make a serious disaster. It is indicated that the interaction between meso-scale convective system inside of typhoon and large scale system in surrounding atmosphere is very important. It is found that the upper level jet steam was observed before typhoon was landing in. And upper lever jet stream, low level jet steam occurred just at the landing time. Because the bottom of clouds inside of typhoon pile up with strong winds at lower levels, the mechanism for down-transfer of momentum is one of the directive reasons for typhoon intensification suddenly. The weather structure for airliner accident in Hongkong international airport is also discussed. The situation of downburst due to the down-transform of momentum is given.