Abstract:Based on the best track data of Tropical Cyclone (TC) in the western North Pacific during 1970-2012 from the Joint Typhoon Warning Center (JTWC) and the ERA-Interim reanalysis data, the extreme weather method was used to determine 30 kt as the threshold of Rapid Intensification (RI), moreover, the temporal and spatial distribution features in RITCs were analyzed. In addition, nine cases from RI samples were selected to conduct comparative analysis on the environmental field of TCRI process by using dynamic composite analysis technique. Results show that (1) RI occurs most frequently in the ocean about 5° east of the Philippine Islands (130°E, 10-15°N), while rarely happens in the South China Sea. (2) RI occurred most possibly in 1972, while least in 2005, and the possibility fluctuation was larger after 1997. (3) The transportation of westerly and southwesterly water vapor associated with the divergence of anticyclone at 150 hPa promotes TCRI activity because of suction effect. (4) During the 24 h before RI and 6 h after RI, the vertical zonal wind shear of the easterly strengthens gradually near the central region of TC, whose value increases from 0.5 m·s-1 to 2.5 m·s-1, then varies between 2.0-3.0 m·s-1, which provides a moderate vertical zonal wind shear near the center of TC to make TCRI conduct.