Increase in western North Pacific tropical cyclone intensification rates and their northwestward shifts

Abstract

The tropical cyclone intensification rates (TCIRs) over the western North Pacific (WNP) are investigated on the basis of 6-hourly atmospheric and oceanic reanalyses and TC best track data from 1982 to 2020. Results indicate that 24-h-TCIRs over the WNP have increased remarkably by ∼17.2% in the past four decades. A remarkable difference before and after the changepoint 2004 is detected in 24-h TCIRs over the WNP basin. The correlation between the TCIR and sea surface temperature (SST) during 2005–2020 shows a significant positive correlation over the western Pacific. Composite analyses of atmospheric and oceanic environments between P1 (1982–2004) and P2 (2005–2020) suggest greater contributions of the underlying SST and relative vorticity (VORT) than those of vertical wind shear (VWS) and mid-tropospheric relative humidity (RH) to TCIR increase. The maximum potential intensity (MPI) has increased since the 1980s, with a significant change from P1 to P2, which further demonstrates that the environmental fields since 2004 are more favorable for TC intensification. At the same time, TCIR geolocation shows a northwestward shift over the TC-active region bounded by 10° ∼ 25°N, 125° ∼ 150°E since 2004, which is possibly modulated by the interdecadal difference of steering flow and ocean state. This study may provide inspirations to clarify the mechanisms of WNP-TCIR interdecadal increase for general TC intensity forecast.