Climatological Characteristics of Rapidly Intensifying Typhoons

Abstract

The occurrence of rapid deepening of tropical cyclones(≥42 mb in 24 h) in the western North Pacific is examined to determine the statistics of these events and to identify features peculiar to their onset. Seventy-nine cases of rapid growth during the period 1956-76 were selected to study climatological characteristics. These data show that the majority (75%) of the deep central pressures(≤920 mb) in the region are attained through the rapid deepening process. The bulk (67%) of these pressure reductions occur over a time interval of 18 h or less with the first 6 h most likely to account for the steepest fall. The statistics reveal that development of a tropical cyclone to typhoon intensity over warm waters (temperature ≥28°C to a depth of 30 m) is a necessary (but not sufficient) prerequisite for rapid deepening. An eye dimension near 40 km also is a frequently observed feature at the onset of rapid deepening. The time of onset occurs most frequently at night. Investigation of typhoon track direction and speed (or changes of these two variables) in relation to abrupt intensificaion revealed little associaion.