Comparison between Wave, Surge, and Inundation Models over Puerto Rico and the U.S. Virgin Islands

Operational storm surge and inundation modeling in U.S. Caribbean and Pacific island waters is challenging. In these reef-fringed island environments, wind waves play a more dominant role in driving storm surge than found for milder-sloped coastlines along the mainland. Since Puerto Rico and the U.S. Virgin Islands are frequented by hurricanes and are well-instrumented, it is an ideal region for model inter-comparison. This project, which forms part of U.S. IOOS’s Coastal and Ocean Modeling Testbed (COMT), has the purpose of evaluating coupled wave and surge models for potential operational implementation at NOAA’s National Hurricane Center and San Juan Weather Forecast Office. The coupled models compared are ADCIRC-SWAN and SLOSH-Wave, a coupling between SLOSH and a new efficient parametric wave model. To assess the development of infra-gravity waves over the fringing reef edge, the phase-resolving model XBeach was nested within the large-scale ADCIRC-SWAN model for a high-resolution domain in the coastal waters near San Juan. The field cases studied are Hurricane Georges (1998) and Hurricane Irene (2011). These are simulated using various representations of the atmospheric forcing, including parametric fields from ATCF data, and gridded output from the CFSv2 and WRF models. The results are first compared in terms of fields of water level, current and wave heights, to assess the impact of wave coupling and differences between the models. Second, the time series of model results are compared to water level and wave height observations at measurement stations. It is found that ADCIRC’s parametric wind forcing and output from the WRF model yield the best agreement with observed surge levels. In the cases considered, the CFSv2-forced simulations yielded poorer agreement to the observed water levels, mainly due to track errors in the atmospheric forcing. The phase-resolved model XBeach was found to capture the infra-gravity band of the wind-wave spectrum on the reef top, which is found in the observations, but absent in the phase-averaged coupled models.