Tropical cyclones intensify mesoscale eddy variability and accelerate Western Boundary Current instability

Yongfei Deng , Tianning Wu, Scott Glenn, Ruoying He

Tropical cyclones strongly disrupt the upper ocean, yet their influence on mesoscale variability in western boundary current systems remains poorly quantified. The Gulf of Mexico, where the Loop Current regularly sheds large warm-core eddies, offers an ideal setting to examine how hurricanes reshape mesoscale dynamics. Using a high-resolution ocean model and hurricane-denial experiments, we analyze the 2024 passage of Hurricanes Helene and Milton and their impacts on the Loop Current Eddy (LC/LCE) mesoscale variability. Hurricane Helene generated pronounced surface cooling by ~0.3°C, weakened the Loop Current, and strengthened the Tortugas cyclonic eddy (CE). Hurricane Milton further enhanced these anomalies and coincided with the detachment of LCE Edison. The combined effect of the two storms was nonlinear: Helene’s cold wake and eddy intensification preconditioned the response to Milton and accelerated eddy separation. Here we show that sequential tropical cyclones can amplify cyclonic vorticity by up to 28%, enhance baroclinic instability through upwelling within the CE, and help boost the LCE shedding by ~6 days earlier, with important implications under a warming climate with more intense storms.