Hurricane Rapid Intensification in the Northern Gulf of Mexico: Recent Evidence of the Role of the Mississippi River Plume

The role of upper-ocean salinity stratification in hurricane rapid intensification (RI), through its impact on ocean mixing and sea surface cooling, has been recognized previously. However, the extent to which the Mississippi River plume plays a role in hurricane RI remains unclear, in part due to limited salinity observations historically over this region. Here we show, using satellite sea surface observations, ocean reanalyses and numerical experiments with an ocean mixed layer model, that the Mississippi River plume played a crucial role in the RI of Hurricane Sally (2020) in the northern Gulf of Mexico. Our analysis reveals that a Loop Current eddy advected low salinity river plume water directly into the path of the storm. Consequently, the enhanced salinity stratification and deepened thermocline reduced the sea surface cooling induced by Hurricane Sally and enabled its RI through a modulation of air-sea enthalpy fluxes. The analysis also indicates that the river plume may have played a role in the RI of other storms in the past besides Sally (2020). Further support for the role of the Mississippi River plume in hurricane RI comes from recent observations from a NOAA/Saildrone uncrewed surface vehicle that went through the eye of Idalia as it intensified in the eastern Gulf. Preliminary results will be presented. The findings for Sally and Idalia highlight the potential significance of the Mississippi River plume for RI predictability in the Gulf of Mexico and point to the operational value offered by increased upper-ocean monitoring in that region.