More autumn tropical cyclone genesis in the South China Sea during El Niño to La Niña transition

Abstract

Previous studies focused on the spatial diversity of ENSO’s influence on tropical cyclones (TCs) in the western North Pacific (WNP), with less emphasis on temporal evolution. This study examines the variability of TC genesis in the WNP during boreal autumn (September-November) across three types of La Niña transitions: cyclic, multi-year, and episodic. The findings highlight significant differences, particularly in the South China Sea’s (SCS) role within the WNP region. During a cyclic La Niña, the SCS TC frequency is approximately 2.6 times greater than those of the other two types due to higher local humidity from increased water vapor transport from the Indian Ocean and convergence in the SCS, driven by an anomalous cyclone in the SCS and Maritime Continent. Observations and model simulations revealed that a warmer sea surface temperature in the Philippine Sea, a delayed effect of the preceding El Niño, triggered this cyclonic circulation and moisture influx.