An Extension to NOAA's Global Multi-Grid WAVEWATCH III Model with Unstructured Coastal Meshes: Development and Validation

The demand for high-resolution forecasts of coastal processes, including wind, water levels, currents and waves has been steadily increasing in recent years. At present, the global operational multi-grid WAVEWATCH III wave model, run by the National Oceanic and Atmospheric Administration's (NOAA) National Centers for Environmental Prediction (NCEP), features a mosaic of regular grids nested in a two-way fashion, from global to shelf scales. At the global scale the grid resolution is 0.5 deg., and in coastal regions it increases to a resolution of up to 4 arc-min (approx.7.5 km at the equator). The latter resolution is insufficient to capture many of the relevant physical process occurring in the coastal zone, and hence does not provide sufficient guidance to NWS forecasters. In this study, a new unstructured version of WW3 is applied to replace the shelf-scale regular grids of NOAA's Global WW3 Multi_1 model with variable-resolution unstructured meshes with cell sizes of down to 1 km. This new system is being developed in order to construct a two-way, wave-surge coupling with NOAA's ADCIRC-based ESTOFS extra-tropical tide and surge model. For this reason, the two models apply the same set of unstructured coastal meshes, atmospheric input, and will run concurrently on NCEP's production machine. This paper discusses the applied meshes, input sources and model settings, and presents the results of a validation study that compares the results of the new system to that of the current regular grid model and observations.