Global and Regional Characteristics of Tropical Cyclone Rapidly Intensifying Events

Accurate prediction of tropical cyclone (TC) intensity still faces great challenges, and rapid intensification (RI) imposes the largest uncertainty in forecasting the TC intensity change. TC RI has been extensively studied, but most studies considered RI during an 24h period, but not the whole life cycle of the RI event. This study investigates the characteristics and environmental factors of ~1500 full lifecycle RI events from 1980 to 2020 in global TCs and compare their regional difference. Our results show that most RI events actually initiate at the tropical storm stage (30-40 kts) preferentially in the early morning, which is consistent across basins. The  locations of RI onsets in the southern hemisphere are generally limited  between 9°S and 20°S, while in the northern hemisphere, they occur at higher latitudes, particularly in the North Atlantic, reaching above 30°N. Nearly half of the RIs last longer than 42h, and RIs in the western North Pacific last significantly longer than RIs in the North Atlantic and South Indian. It is interesting that no matter the initial intensity, RI events with longer duration have higher intensification rate (INTRATE), except for extremely lasted events. Also, the total intensification amplitudes of RIs are more determined by the duration than the INTRATE. Overall, the duration and INTRATE of RIs have a positive relationship with maximum potential intensity (MPI), SST and mid-level relative humidity, and a negative relationship with vertical wind shear. Of course, the initial environmental conditions for RIs are more favorable than regularly intensifying events. It is intriguing whether environments of extreme RIs (extremely high INTRATE) differ from normal RIs, which will be further investigated.