Investigation of Extreme Weather, Ocean Current, Wave, and Coastal Flooding during Hurricane Florence (2018) Using the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) Model

Hurricane Florence (2018) was a devastating storm that brought record-setting rainfall and flooding to the Carolinas. Hurricanes are intrinsically connected to the coastal environment they transit, and methods of incorporating ocean and surface-wave feedback are essential for accurate prediction of atmosphere and ocean dynamics before, during, and after landfall. We utilize a suite of coupled and uncoupled model simulations to investigate the impact of a fully-resolved ocean and surface wave environment on storm characteristics (e.g., strength, intensity, track, precipitation, among others).

Several ocean surface roughness parameterizations based on wave height, length, period, and direction have been implemented. These modify the fluxes of heat, freshwater, and momentum between the Weather Research and Forecasting (WRF) atmospheric model, the Regional Ocean Modeling System (ROMS) ocean model, and the Simulating WAves Nearshore (SWAN) model, as implemented in the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system. We demonstrate that the roughness parameterizations are important to the fluxes of sensible heat, latent heat, and momentum, ultimately leading to changes in the storm wind field and storm surge.

We have also developed methods to incorporate hindcast wave fields from the WaveWatch 3 surface-wave model into the suite of WRF Preprocessing System (WPS) utilities for ingestion into the WRF model. We examine the impacts of utilizing WaveWatch 3 hindcast surface wave fields versus fully-coupling the ocean, atmosphere, and surface waves within the COAWST modeling system. In order to provide the most direct comparison, we use the same routines as built into COAWST but transfer the fields from the WaveWatch 3 hindcast, rather than from a coupled SWAN model. Our results show improvement through addition of the hindcast WaveWatch 3 model fields while adding little computational expense to our simulations. The improvement demonstrated in our coupled and uncoupled simulations are completed with the aim of further coupling to the WRF-Hydro hydrological model for use with the National Water Model to deliver accurate, real-time flood and storm surge forecasting for stakeholders in coastal communities.