Study on the Cause of Torrential Rain Associated with Landfalling Typhoon Vicente

By using conventional meteorological data,data from regional automatic weather stations,and NECP / NCAR 1° × 1° 6-hourly reanalysis data,a torrential rain in the Pearl River Delta and western Guangdong province which was under the influence of the landfalling typhoon Vicente( 1208) is analyzed.The circulation situation,convergence and divergence condition,Southwest Monsoon activities and water vapor transport are analyzed for the time after Vicente landed. The results are shown as follows: 1) As a West Pacific subtropical high pressure ridge was westward and strengthened and the ridge line position maintained,the typhoon's northward movement was restrained,being beneficial to its mild post-landing moving speed and providing a stable background field to the persistent rain in Vicente 's northwest-bound process. 2) The strengthening of two equatorial flows near 100°E and 108°E and a Somali jet caused the Southwest Monsoon to develop,adding abundant amount of water vapor,heat and momentum to the rainfall after landfall and being beneficial to the maintenance of the rainfall. Meanwhile,a band of high- value water vapor transportation passed through Indochina and supplied water vapor to typhoon circulation continuously. With the effect of the typhoon moving northwest after landing and a band of big values of the westerly moving northwards,a big- value area of water vapor flux and a big- value area of moisture flux divergence were correspondingly moving north,which had a certain role in the increase of heavy rain. 3) After landing,the upper divergence significantly strengthened. It was stronger than the low- level convergence. A jet stream flowing out of high levels had a strong sucking effect,which supplied dynamic lifting to the occurrence of heavy precipitation.