Decadal changes in tropical cyclone activity over the western North Pacific in the late 1990s

Abstract

A pronounced decadal change in tropical cyclone (TC) activity over the western North Pacific (WNP) in the late 1990s was identified. Based on a comparison of the two epochs that occurred before and after the late 1990s, the TC genesis number exhibited an evident decrease over the southern WNP (S-WNP: 5°–20°N, 105°–170°E) and an increase over the northern WNP (N-WNP: 20°–25°N, 115°–155°E), which partly corresponded to a significant northward migration in the seasonal mean latitudinal location of TC genesis, i.e., from 17.2°N to 18.7°N. After the late 1990s, the northwestward-moving track became the most dominant track mode, accompanied by the weakening of both the westward-moving track and the northeastward-recurving track. Meanwhile, the TC occurrence frequency (TCF) experienced evident increases over southeastern China and the Okinawa islands, while prominent decreases occurred over the South China Sea, the Philippine Sea, Japan and east of Japan. Changes in the TCF were determined by TC genesis changes, TC track shifts and variations in regional TC durations, which were all ascribed to the decadal change in tropical Indo-Pacific sea surface temperature. The full picture on the decadal changes in the WNP TC activity revealed in this study may provide useful guidance for regional TC seasonal forecasts and future projections.