Plain Language Summary

Rapid intensification (RI) is commonly recognized as a sharp increase in tropical cyclone (TC) intensity over a short duration, posing a significant challenge for operational TC forecasting. Given concerns about climate change and its impacts on TC activity, there has been an increasing focus on temporal variations of RI. Unlike most previous publications investigating changes in RI occurrence, this study focuses on the interannual variability of RI magnitude, defined as the TC intensity increase during the 24-hr RI stage. There is a significant interannual correlation between basin-averaged RI magnitude over the western North Pacific during July–November and the simultaneous Western Pacific (WP) teleconnection index from 1982 to 2021. During a positive WP, RI magnitude significantly increases over the southwestern quadrant of the basin because of significantly reduced 850–200-hPa vertical wind shear. RI magnitude weakly decreases over the northern part of the basin, likely linked to slightly enhanced vertical wind shear. These vertical wind shear changes can be further linked to WP-induced circulation anomalies at lower and upper levels. Our results highlight the dominant (lesser) role of vertical wind shear (850-hPa relative vorticity) in controlling the interannual variation of RI magnitude over the western North Pacific.

Abstract

Abstract This study investigates the interannual variability of rapid intensification (RI) magnitude of western North Pacific (WNP) tropical cyclones. There is a significant correlation between basin-averaged RI magnitude during July–November and the simultaneous Western Pacific (WP) teleconnection index from 1982 to 2021. RI magnitude is, on average, larger (smaller) in positive (negative) WP phases. During a positive WP, RI magnitude changes exhibit a southwest-northeast dipolar pattern, with significant increases over the southwestern quadrant of the WNP and weak decreases over the northern part of the WNP. The WP teleconnection relates to RI magnitude primarily through modulation of 850–200-hPa vertical wind shear, with less influence from 850-hPa relative vorticity. The changes in these two dynamic conditions can be linked to WP-induced circulation anomalies at lower and upper levels. Our results highlight that different contributors may be responsible for changes in WNP RI occurrence and RI magnitude.