Hurricane-induced differential mixed layer cooling over strong oceanic background flows

Strong horizontal advection and isotherm topography in mesoscale oceanic features of the Gulf of Mexico (GOM) have been previously shown to impact the efficiency of hurricanes to cool the ocean mixed layer (OML), affecting the hurricane energy source and inducing storm intensity fluctuations. Understanding the degree of hurricane-induced OML cooling over strong oceanic background flow has important implications for oceanic feedback to hurricane intensity.

To illustrate the point above, three-dimensional measurements acquired in the GOM during the interaction of Hurricanes Katrina and Rita (2005) with the strong geostrophic flow in the Loop Current System, and idealized numerical experiments of hurricane-induced OML entrainment over mesoscale oceanic eddies, underscore the importance of the OML topography and circulation on hurricane intensity changes. Both storms deepened to category 5 status during interaction with warm oceanic features, then weakened after encountering a cold eddy prior to making landfall. Profiler measurements indicated that during both storms, increased cooling (4 to 5 ^oC) was associated with shallower OML in cold eddies, while reduced cooling (<2 ^oC) occurred in thicker OML in warm oceanic features. Froude numbers larger than 1 over the cold eddies indicated a stronger baroclinic response with increased vertical shear-driven cooling. The storms' cold wake was confined and advected by the strong oceanic background flow. The spatial variability of the oceanic background flow, often not captured by satellite-derived sea surface temperature distributions that prevail in the GOM during the hurricane season, must be accounted for in 3-D coupled models to improve hurricane-induced OML cooling and intensity forecasting.