Enhanced Sea Surface Cooling and Suppressed Storm Intensification During Slow-Moving Track-Turning Stage of Tropical Cyclones

Abstract

Tropical cyclones (TCs) often undergo track turning when moving over the ocean. However, the influence of track turning on TC-ocean interactions remains little explored. This study systematically investigates sea surface temperature (SST) cooling and TC intensification during TC track-turning stages in global TC-active basins during 1998–2022. Globally, turning TCs induce stronger SST cooling than straight-moving TCs (e.g., −1.53°C vs. −1.08°C for categories 1–2), expand cooling area by 40%–110%, and greatly reduce cooling asymmetry for left-turning (right-turning) TCs in the Northern (Southern) Hemisphere. The translation speed of turning TCs is 1.5 m s⁻¹ slower compared to straight-moving TCs. Numerical experiments demonstrate that the enhanced cooling is attributed to the combined effect of track turning and accompanying slow translation speed. The enhanced cooling effectively suppresses storm intensification of turning TCs. The intensification rate for straight-moving versus turning TCs is 2.98 versus 0.06 m s⁻¹ per 24 hr for categories 1–2. As turning angle increases, cooling magnitude increases and intensification rate decreases. The probability of rapid intensification for turning TCs is about one-third lower than that for straight-moving TCs. Consequently, TCs with smaller turning angles are more likely to develop into intense TCs. Operational forecast models underforecast turning angles of turning TCs and thus overforecast TC intensity with forecast errors increasing with turning angle. This study demonstrates that TC track-turning stages play a crucial role in modulating TC intensification via an oceanic pathway, highlighting that improving track turning forecast will contribute to enhancing TC intensity forecast accuracy.