Hurricane wind-driven surface waves on a narrow continental shelf and exposed coast

Abstract

Tropical cyclones, including hurricanes, have high winds that can generate strong ocean surface circulation and large surface waves and numerous hurricanes that form and propagate over the Atlantic Ocean interact with the continental shelf. Hurricane Florence (2018) impacted the east coast of North America after moving across the narrow shelf and made landfall in Onslow Bay, North Carolina, USA. In contrast, Hurricane Isaias (2020) moved generally parallel to the continental shelf, making landfall in Onslow Bay along a very different track compared to Hurricane Florence. These hurricanes provide an opportunity to understand the waves generated by large storms that move across the open ocean to the coastal environment on the shelf. In this study, the coupled Delft3D-SWAN modelling system is applied to numerically simulate the wind and wave conditions during both Hurricane Florence and Hurricane Isaias. The simulations are analyzed to understand the source terms that control the generated and dissipation of the surface wave field. The model results for Hurricane Florence, indicated that the deep water terms (wind input, whitecapping and quadruplet wave interactions) governed wave action balance on the shelf and in Onslow Bay (10–100 m depths), with negligible contributions from the shallow water dissipation terms such as bottom friction. Hurricane Isaias followed the same trend, but with lower values corresponding to lower wind speeds and smaller wave heights. In addition, Hurricane Florence crossed the shelf and approached the bay from the open ocean with larger waves that were not limited by fetch. In contrast, since Hurricane Isaias followed the coast along the shelf, the wave conditions were fetch-limited on the west side of the track near the coast and not limited by fetch on the east side on the open shelf. The results of this study underscore how hurricanes with different tracks with respect to the orientation of the shelf and coast generate different wave fields and impact coastal environments in different ways.