Ocean-Atmosphere Observations from Uncrewed Saildrones during the 2023 Atlantic Hurricane Season: Summary and Initial Results

During the 2023 Atlantic hurricane season, 12 Saildrone uncrewed surface vehicles (USVs) were deployed in the western Atlantic Ocean, Caribbean Sea, and Gulf of Mexico with the goal of collecting ocean-atmosphere data within hurricane eyewalls. Nine different USVs intercepted tropical storms and hurricanes a total of 19 times, all with sustained wind measurements of at least tropical storm force (34 kt). Two USVs measured sustained hurricane-force winds (64+ kt) in the eyewalls of Hurricanes Idalia and Lee. This presentation gives an overview of the 2023 mission and initial results, focusing on the interaction of Hurricane Idalia with the Mississippi River plume as it rapidly intensified in the eastern Gulf of Mexico in August. Saildrone observations and ocean model experiments show that strong salinity stratification associated with the Mississippi plume reduced sea surface temperature cooling under the core of the hurricane by 0.6-0.8C, aiding its intensification. Historical surface salinity data from satellites going back to 2010 reveal three other occurrences of the Mississippi plume extending far southward into the eastern Gulf in August (2014, 2015, 2019), emphasizing the need for continued monitoring of ocean conditions in that area during future hurricane seasons.