Possible Influence of Tropical Indian Ocean Sea Surface Temperature on the Proportion of Rapidly Intensifying Western North Pacific Tropical Cyclones during the Extended Boreal Summer

Abstract

This study examines the possible impact of tropical Indian Ocean (TIO) sea surface temperature anomalies (SSTAs) on the proportion of rapidly intensifying tropical cyclones (PRITC) over the western North Pacific (WNP) during the extended boreal summer (July–November). There is a robust interannual association (r = 0.46) between TIO SSTAs and WNP PRITC during 1979–2018. Composite analyses between years with warm and cold TIO SSTAs confirm a significant impact of TIO SSTA on WNP PRITC, with PRITC over the WNP basin being 50% during years with warm TIO SSTAs and 37% during years with cold TIO SSTAs. Tropical cyclone heat potential appears to be one of the most important factors in modulating the interannual change of PRITC over the WNP with a secondary role from midlevel moisture changes. Interannual changes in these large-scale factors respond to SSTA differences characterized by a tropics-wide warming, implying a possible global warming amplification on WNP PRITC. The possible footprint of global warming amplification of the TIO is deduced from 1) a significant correlation between TIO SSTAs and global mean SST (GMSST) and a significant linear increasing trend of GMSST and TIO SSTAs, and 2) an accompanying small difference of PRITC (~8%) between years with detrended warm and cold TIO SSTAs compared to the difference of PRITC (~13%) between years with nondetrended warm and cold TIO SSTAs. Global warming may contribute to increased TCHP, which is favorable for rapid intensification, but increased vertical wind shear is unfavorable for TC genesis, thus amplifying WNP PRITC.