Observations of Coastal Ocean-Atmosphere Interactions From Three Tropical Cyclones During the Fall Transition of 2017 in the Mississippi Bight, Northern Gulf of Mexico

Abstract

Overlap between peak hurricane (i.e., strong tropical cyclone) activity and the fall transition represents a period when coastal ocean-hurricane interactions can be highly variable due to rapid changes in seasonal hydrographic conditions. However, understanding of the response of the coastal ocean to tropical cyclone passage is limited due to the difficulty of collecting observations during such extreme events. Here, observations on the shelf were used to investigate coastal ocean-atmosphere interactions during the passage of three tropical cyclones in the northern Gulf of Mexico during the fall of 2017. Tropical depression conditions associated with Hurricanes Harvey and Irma and Hurricane Nate impacted the Mississippi Bight region within a 6-week span (late August–early October) when the fall transition typically begins. Despite large impacts from Harvey and Irma, which pushed the system into a marine cold spell, a rewarming event changed the trajectory of the fall transition, extending the period when the shelf temperature remained favorable for hurricane intensification. In contrast, Nate, the most direct storm hitting the study area, had minimal impacts on shelf conditions, even at sites within the inner core of the storm. All storm responses were linked to moisture disequilibrium and direction of the across-shelf wind where southward offshore (northward onshore) winds generated higher (lower) vertical gradients in humidity. Overall, these events show the impact that even distant hurricanes can have on the fall transition as well as highlight the need for improving the understanding of factors that influence thermodynamic disequilibrium in the coastal zone.