Drivers of Coastal Flooding along South-Atlantic Bight during Hurricanes Dorian and Matthew

During the fall of 2016 and 2019, the Southeast coast of the United States experienced the passage of hurricanes Matthew and Dorian. While the tracks and intensities of these storms were comparable along South-Atlantic Bight, their impacts in terms of coastal flooding were dramatically different. Matthew produced significant flooding in excess of 1.5 meter above mean higher high water (MHHW) levels along the South-Atlantic Bight, while Dorian did not lead to any widespread flooding in the area. Using an unstructured 3-dimensional coastal model that is able to resolve the city-scale (~up to 10-meter resolution), we examine the relative roles of multiple drivers of coastal flooding and water level response along the Georgia coast and city of Savannah. Sensitivity analysis performed with the model show that the compounding effects of different sea level drivers (e.g. rainfall and river runoff, tides, winds, large-scale ocean circulation) played a key role in determining differences between Dorian and Matthew in terms of coastal flooding and water level. Specifically, the response and coastal impacts of the large-scale ocean circulation (e.g. Gulf Stream) was very similar during both hurricanes. However, low tides along the coast played a role in mitigating the impact of Dorian compared to Matthew. In contrast, during Matthew, the estuarine circulation dynamics had a significant impact on inland coastal flooding owing to the extreme precipitation and river runoff. By incorporating the multiple drivers of coastal flooding, the coastal sea level dynamical model is able to give accurate predictions of water level at the city scale beyond what is currently available from traditional coastal forecasting systems.