Increasing trend in rapid intensification magnitude of tropical cyclones over the western North Pacific

Rapid intensification (RI) refers to a significant increase in tropical cyclone (TC) intensity over a short period of time. A TC can also undergo multiple RI events during its lifetime, and these RI events pose a significant challenge for operational forecasting. The long-term tendency in RI magnitude of TCs over the western North Pacific is investigated in this study. During 1979-2018, a significant increasing trend is found in RI magnitude, which primarily results from the significant increasing number of strong RI events, defined as 24 h intensity increases of at least 50 kt. Furthermore, there are significantly more (slightly fewer) strong RI occurrences west (east) of 155 degrees E in 1999-2018 than in 1979-1998. Significant increases in strong RI occurrences are located over the region bounded by 10 degrees similar to 20 degrees N, 120 degrees similar to 150 degrees E. These changes are likely induced by the warming ocean but appear uncorrelated with changes in the atmospheric environment. By contrast, there are slight decreases in strong RI occurrences over the region bounded by 12.5 degrees similar to 22.5 degrees N, 155 degrees similar to 170 degrees E, likely due to the offset between RI-favorable influences of the warming ocean and RI-unfavorable influences of increasing vertical wind shear (VWS).