Cascading Weather Events Amplify the Coastal Thermal Conditions Prior to the Shelf Transit of Hurricane Sally (2020). Issue 12 (13th December 2021)

• Record Type: Journal Article
• Authors: Dzwonkowski, B.; Fournier, S.; Lockridge, G.; Coogan, J.; Liu, Z.; Park, K.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 12(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-13
• Subjects: tropical cyclones -- coastal ocean -- cascading events -- temperature -- downwelling -- Hurricane Sally; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017957
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Changes in tropical cyclone intensity prior to landfall represent a significant risk to human life and coastal infrastructure. Such changes can be influenced by shelf water temperatures through their role in mediating heat exchange between the ocean and atmosphere. However, the evolution of shelf sea surface temperature during a storm is dependent on the initial thermal conditions of the water column, information that is often unavailable. Here, observational data from multiple monitoring stations and satellite sensors were used to identify the sequence of events that led to the development of storm‐favorable thermal conditions in the Mississippi Bight prior to the transit of Hurricane Sally (2020), a storm that rapidly intensified over the shelf. The annual peak in depth‐average temperature of >29°C that occurred prior to the arrival of Hurricane Sally was the result of two distinct warming periods caused by a cascade of weather events. The event sequence transitioned the system from below average to above average thermal conditions over a 25‐day period. The transition was initiated with the passage of Hurricane Marco (2020), which mixed the upper water column, transferring heat downward and minimizing the cold bottom water reserved over the shelf. The subsequent reheating of the upper ocean by surface heat flux from the atmosphere, followed by downwelling winds, effectively elevated shelf‐wide thermal conditions for the subsequent storm, Hurricane Sally. The coupling of climatological downwelling winds and warm sea surface temperature suggest regions with such characteristics are at an elevated risk for storm intensification over the shelf. Plain Language Summary: Changes in tropical cyclone intensity prior to landfall represent a significant risk to human life and coastal infrastructure. Such changes can be influenced by sea surface temperatures as they provide the energy to tropical cyclones. However, the changes in sea surface temperatures during a storm depend on heat content in the coastal ocean before the storm arrives and the relevant information is often unavailable. Measurements from multiple monitoring stations and satellite sensors were used to identify the events that led to the development of favorable temperatures in the Mississippi Bight prior to the arrival of Hurricane Sally (2020), a storm that rapidly intensified. A sequence of two warming periods transitioned the coastal ocean from below average to above average temperatures over a 25‐day period. The transition was initiated by Hurricane Marco (2020) which pumped heat from the ocean surface to deeper waters. This was followed by a reheating of the upper ocean and the offshore transport of warm coastal waters across the bottom of the shelf which packed the shelf with thermal energy that could feed the subsequent storm. The results suggest that coastlines with certain ocean and wind conditions may have an elevated risk of storm strengthening before landfall. Key Points: Annual peak in depth‐average temperature occurred prior to shelf transit of Hurricane Sally providing favorable intensification conditions Depth‐average temperature was set up by a distinct cascade of weather events including persistent downwelling conditions Coupling of climatological downwelling winds and warm ocean temperatures suggests an elevated risk of storm intensification over the shelf