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

This study examines the possible impact of tropical IndianOcean (TIO) sea surface temperature anomalies (SSTAs) on the proportion of rapidly intensifying tropical cyclones (PRITC) over thewestern North Pacific (WNP) during the extended boreal summer (July-November). There is a robust interannual association (r=0.46) between TIO SSTAs andWNPPRITC during 1979-2018. Composite analyses between yearswithwarm and cold TIO SSTAs confirma significant impact ofTIOSSTAonWNPPRITC, 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 themost important factors inmodulating the interannual change of PRITC over theWNP with a secondary role from midlevel moisture changes. Interannual changes in these large-scale factors respond to SSTA differences characterized by a tropics-widewarming, implying a possible globalwarming amplification onWNPPRITC. 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 ofGMSST andTIO SSTAs, and 2) an accompanying small difference of PRITC (similar to 8%) between years with detrended warm and cold TIO SSTAs compared to the difference of PRITC (similar to 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.