Contrasting mechanisms of two rapid intensifications in Typhoon Hinnamnor (2022) under marine heatwave conditions

Contrasting mechanisms of two rapid intensifications in Typhoon Hinnamnor (2022) under marine heatwave conditions

Kai Liu¹, Xiaojiang Song¹, Xingrong Chen¹

^1.National Marine Environmental Forecasting Center, Beijing 100081, China

Previous studies indicate that tropical cyclone (TC) rapid intensification (RI) predominantly occurs between 8°N and 20°N in the Northwest Pacific. However, under ongoing global warming, the increasing frequency of marine heatwaves (MHWs) at mid to high latitudes and the poleward shift of peak TC intensity suggest that MHWs may increasingly facilitate RI beyond this traditional latitude range. Super Typhoon Hinnamnor (2022) provides a unique example, being the only TC during 1982-2023 to maintain strong intensity north of 25°N while undergoing two RI events under pronounced MHW conditions.

This study reveals distinct roles of MHWs modulated the two RI events of Hinnamnor through fundamentally different upper-ocean vertical structures. The first RI, lasting 18 hours and intensifying the storm from a strong tropical storm to a super typhoon, was primarily ocean-driven. The MHW penetrated into the subsurface, deepening the warm layer and sustaining high upper-ocean heat content (UOHC). A thick barrier layer, preserved by relatively fast storm motion, enabled a subsurface “heat pump” effect that supported sustained intensification. In contrast, the second RI was short-lived (6 hours) and involved only a one-category intensification. A shallow mixed layer confined warming to the surface, enhanced vertical mixing and cold-water upwelling, prematurely terminating the second RI.