Influence of sea surface temperature patterns and mean warming on past and future Atlantic hurricane activity

Emma Lilly Levin, Gabriel Vecchi, Wenchang Yang 

This study investigates the relative contributions of large-scale thermodynamic and dynamic processes to multidecadal changes in Atlantic tropical cyclone (TC) activity, spanning the historical record since the late 19th century, and extending to 2100 projections. We employ a framework that decomposes TC counts into precursor disturbances that transition into fully developed storms, applied to multi-ensemble simulations of two TC-permitting atmospheric models forced with observationally-constrained and projected sea surface temperatures (SSTs). This design allows us to isolate the effects of patterns of SST change from global mean warming on Atlantic TC activity. Our results show that multidecadal trends in TC frequency are primarily governed by two thermodynamic variables: potential intensity and moist entropy deficit. In the historical record, these variables reinforced one another, producing more robust trends in TC activity. In contrast, future projections suggest opposing influences, with one variable (potential intensity) becoming more favorable for TCs while the other (moist entropy deficit) becomes less favorable, leading to increased uncertainty in TC projections. We trace this shift to differences in relative warming between the tropical Atlantic and the broader tropics, underscoring that regional SST patterns—rather than the global mean warming rate—control both past variability and projected future changes in TC activity. Constraining future patterns of warming is therefore essential for improving the reliability of TC projections.