Tracing Oceanic Sources of Heat Content Available for Atlantic Hurricanes

In the Main Development Region (MDR) for Atlantic hurricanes, the volume of water warmer than 26.5 degrees C quantifies the potential source of energy for major storms. Taking a Lagrangian perspective, this warm water is backtracked on seasonal timescales in an eddy-resolving ocean model hindcast spanning 1988-2010. Being confined near the surface and assuming a mixed layer depth of 50 m, net heat fluxes into or out of water parcels advected toward the MDR are inferred from along-trajectory temperature tendencies. To first order, these heat fluxes match surface net heat fluxes during the months over which water advects into the region. Contributions to this warm water in the preceding 6 months include water resident in the MDR (20%-40%), arriving via the North Brazil Current (NBC, 5%-15%), or via Ekman drift across 10 degrees S. In relative terms, decreased contributions from the NBC and Ekman drift and more in situ warming within the MDR lead to warmer, more active hurricane seasons. Plain Language Summary More and stronger hurricanes can be maintained by a larger quantity of warm ocean water in the North Atlantic. This water can be tracked backwards through time in high resolution model data to see where it originated. While some of the warm water is already in the tropical Atlantic 6 months before the hurricane season, some moves into the area via ocean currents or is pushed northwards by local winds. More and stronger hurricanes are more likely to occur in years where there is less movement of water into the tropical North Atlantic, along with more local heating of the region in the months leading into the hurricane season.