The applications of UFS-Coastal v1.0.0b01: wave-current coupling of SCHISM and WAVEWATCH III

Abstract. Accurate prediction of coastal flooding and nearshore processes requires a coupled modeling framework that resolves interactions among ocean circulation, surface waves, ice, and atmospheric forcing across complex coastal geometries. To address this need, we present Unified Forecast System Coastal model (UFS-Coastal), a coupled coastal modeling framework extending the Unified Forecast System Weather Model (UFS-WM). The UFS-Coastal was developed to address this need by disentangle extending the prior infrastructure (called CoastalApp), and combining CaostalApp and UFS-WM, and byintegrating four different coastal hydrodynamic models: SCHISM, ADCIRC, FVCOM, and ROMS, along with the spectral wave model WAVEWATCH III (WW3) and CICE within a unified coupled framework. Here we introduce UFS-Coastal to the community, and focus on one particular aspect, the wave-current coupling between SCHISM and WW3 with two methods: the Longuet-Higgins radiation stress formulation and a three-dimensional (3D) vortex approach. We provide a comprehensive description of UFS-Coastal’s infrastructure, coupling methodologies, and its automated regression testing framework. The system’s performance is demonstrated through experiments in the Duck, North Carolina (NC) region against Field Research Facility observations. Both wave-current coupling schemes between the SCHISM and WW3 could successfully reproduce observed coastal hydrodynamics and wave conditions; notably, the 3D vortex coupling improved simulations of wave-induced mixing in shallow and stratified environments. Overall, UFS-Coastal offers a robust framework for accurate prediction of coastal flooding, storm surge events, and wave-current interactions, supporting both research and operational forecasting applications.