Oceanic and Atmospheric Controls on Tropical Cyclone Activity

Tropical cyclones (TCs) are among the deadliest and costliest natural hazards. Seasonal to centennial TC prediction requires understanding and modeling the physical relationships between TCs and climate variability on multiple spatial scales. One major source of TC predictability is sea-surface temperature (SST) - in both local and remote basins - which influences the thermodynamic and dynamic environment of TCs and can be predicted in advance of the TC season. I will discuss the compensating and constructive influences of Atlantic and Pacific SST variability on TCs. In addition, I will present the mechanisms by which TCs respond to various patterns of tropical Pacific warming during El Niño. Specifically, TC-permitting tropical channel model simulations indicate that Atlantic TC activity is more effectively suppressed by SST warming in the central, compared to eastern Pacific. This is because less warming is required near the West Pacific warm pool, compared to the East Pacific cold tongue, to satisfy the SST threshold for deep convection, which leads to Atlantic TC suppression via vertical wind shear enhancements associated with the Walker Circulation. Finally, I will show that Atlantic TCs are not limited by their typical precursor, African easterly waves (AEWs), on seasonal-climate timescales, using regional climate model experiments in which AEWs are prescribed in or filtered from the lateral boundary condition. This suggests that Atlantic TCs will generate by other mechanisms in the absence of AEWs. Altogether, this research highlights the importance of two considerations when interpreting the influence of SST anomalies on TC activity: 1) the background SST state, due to the non-linear response of deep convection to SST, and 2) across-basin SST patterns, due to combined local and remote influences.