An Abrupt Slowdown of Late Season Tropical Cyclone over the Western North Pacific in the Early 1980s

Translation speed is an important factor determining locally accumulated disasters induced by tropical cyclones (TCs). We found that the basin wide TC translation speed over the western North Pacific (WNP) in the late season (October–December) experienced an abrupt decrease in the early 1980s. However, this slowdown cannot be explained by the previously proposed deceleration in large-scale steering. In this study, we demonstrated that this slowdown results from the decreased proportion of subtropical TC track frequency in the early 1980s. Because late-season large-scale steering flow in the subtropical WNP is much greater than that in the tropical WNP, TCs influencing the subtropical WNP generally hold greater translation speed than that of TCs staying in the tropical WNP. Thus, a decrease in the ratio of subtropical TC track frequency can lead to a notable decrease in the basin wide TC translation speed. The decreased ratio of subtropical TC track frequency results from the strengthened southwestward steering and the reduced ratio of TC genesis in the tropical eastern WNP, which is linked to a WNP anticyclonic circulation that appears to be driven by the Atlantic Multi-decadal Oscillation. The result introduces the crucial role of TC track shift in the basin wide TC translation speed and has important implications for understanding the effects of climate change on TC translation speed.