Role of tropical cyclones and salinity stratification in the expansion of a coastal marine heatwave

Marine heatwaves (MHWs) during peak hurricane season can impact storm intensification, posing a significant threat to coasts and ecosystems. However, understanding of salinity stratification in the evolution of MHWs in river-dominated, hurricane-prone coastal regions is limited. Here, the event sequence leading to a large-scale coastal MHW in the Gulf of Mexico during the 2019 hurricane season was investigated. Both atmospheric and oceanic events coupled to drive the shelf-wide evolution of this full water-column MHW with surface heat fluxes, vertical mixing, and advection all contributing. In particular, several tropical cyclone events modified the vertical structuring of the MHW, and none intensified over the study region. During the decay phase, low salinity from freshwater discharge resulted in temperature inversions, leaving the bottom layer MHW preserved for an extended period. This study highlights the importance of salinity dynamics on MHWs and nearshore environmental conditions in intensity forecasting of landfalling storms.