Interbasin Analysis of the Poleward Expansion of Tropical Cyclone Potential Intensity

Abstract Favorable thermodynamic environments for tropical cyclone (TCs), as measured by potential intensity (PI), expand to higher latitudes in a warming climate, in both observations and future simulations. However, this expansion rate has yet to be compared systematically between hemispheres and across basins. This work quantifies the poleward expansion of PI globally and compares it across basins using ERA5 reanalysis and an ensemble of CMIP6 historical and future climate scenarios. We quantify trends in the latitude of PI thresholds associated with TC intensity and directly decompose PI trends into thermodynamic drivers using a novel PI budget equation that distinguishes Clausius‐Clapeyron response to warming from other effects. Our results show that PI consistently expands strongly poleward near Western Boundary Currents (WBCs) in the Western North Pacific, North Atlantic, South Indian, and South Pacific. It expands slowly near EBCs in the Eastern North Pacific and South Indian basins. Basins with WBC outflow exhibit enhanced coastal PI trends linked to SST warming, outflow cooling, and poleward ocean heat transport. Southern Hemisphere basins display weaker expansion, except near strong WBCs. CMIP6 models capture this east‐west asymmetry in PI trends across basins, but underestimate the magnitude of poleward expansion rates due to misrepresenting changes in outflow temperature and near‐surface air temperature and humidity. Our analysis suggests that ocean circulation plays a critical role in shaping regional PI trends and future increases in TC risk at higher latitudes will be unevenly distributed and may depend locally on the orientation of the coastline relative to oceanic boundary currents.