Upper ocean mixing, surface heat fluxes, and heat content variability in the upper 150 m during Hurricane Laura (2020)

This study integrates thermistor observations, hurricane glider measurements, and model-derived temperatures to examine the oceanic processes influencing Hurricane Laura’s rapid intensification, the role of the preexisting warm mixed layer at Stone Mooring (StM) in modulating cooling of the mixed layer, and the processes governing mixed layer heat evolution during and after storm. Prior to the storm’s passage, StM featured a 31°C warm mixed layer and elevated heat content (60–80 kJ/cm2), which strongly preconditioned the upper ocean. Thermistor data showed that Hurricane Laura produced a mixed layer cooling of 1.2°C on 26 August, compared with a model-estimated cooling of −1.04°C. A 1D shear-driven mixed layer model experiment indicates that, without the warm preexisting mixed layer, temperatures could have cooled down to 28.53°C, supporting the hypothesis that thermal structures associated with Loop Current warm core eddies rarely experience substantial cooling during hurricane passage. We also show that relatively small surface heat fluxes (5.04 kJ/cm2) sustained Hurricane Laura during intensification at StM. Mixed layer heat budget analysis shows that entrainment and surface heat fluxes were the primary drivers of the observed temperature tendency. These results improve understanding of upper ocean processes and demonstrate that observations from StM provide valuable constraints for operational hurricane models in the Gulf of Mexico.