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The Met Office operational wave forecasting modelling system runs four times a day to provide global and regional forecasts up to 7 d ahead. The underpinning model uses a recent development branch of the third-generation spectral wave model WAVEWATCH III® (version 7.12) that includes several updates developed at the Met Office. These include the spherical multiple-cell (SMC) grid, a rotated pole grid formulation for mid-latitudes, enhancements to OASIS coupling and updates to the netCDF postprocessing. Here we document the technical details behind the system with a view to further developments. The operational system includes a global forecast deterministic model (GS512L4EUK) and two regional models nested one-way covering the Northwest (NW) European shelf and UK waters (AMM15SL2, where AMM is for Atlantic Margin model) in addition to an Atlantic wave ensemble (AS512L4EUK). GS512L4EUK and AS512L4EUK are based on a multi-resolution four-tier SMC 25-12-6-3 km grid. The regional AMM15SL2 configuration uses a two-tier SMC 3-1.5 km grid and is run operationally both as a standalone forced model (includes wave–current interactions) and as the wave component of a two-way ocean–wave coupled operational system. Model evaluation is focused on the global and regional baseline configurations. Results show evidence of resolution-dependent differences in wave growth, leading to slightly overestimated significant wave heights in coastal mid-range conditions by AMM15SL2 but an improved representation of extremes compared to GS512L4EUK. Additionally, although a positive impact of the surface currents is not always shown in the overall statistics of the significant wave height due to a larger spread in the observation–model differences, wave–current effects help to better capture the distribution of the energy in terms of frequency and direction near the coast (>20 % improvement), which has implications to beach safety, coastal overtopping risk and shoreline evolution. Future system developments such as the use of sea point wind forcing, the optimisation of the models in line with model resolution and the utilisation of SMC multi-grids are discussed. [ABSTRACT FROM AUTHOR]

The Met Office operational wave modelling system is an operational forecast system run four times daily at the Met Office to provide global and regional forecasts up to 7 days ahead. The underpinning model uses a recent development branch the spectral wave model WAVEWATCH III® (version 7.12) that includes a number of updates developed at the Met Office. Code contributions include the Spherical Multiple-Cell (SMC) grid, rotated pole grid formulation for mid latitudes, enhancements to OASIS coupling and updates to the netCDF postprocessing. Here we document and describe the technical details behind the Met Office operational system of WAVEWATCH III® configurations with a view to further development. These include a global forecast deterministic model (GS512L4EUK) and two regional models nested one-way covering the Northwest (NW) European shelf and UK waters (AMM15SL2) as well as an Atlantic wave ensemble (AS512L4EUK). GS512L4EUK and AS512L4EUK are based on a four-tier SMC 25-12-6-3km grid refinement where currents are not included. AMM15SL2 is run operationally both as a standalone forced model and as the wave component of a two-way ocean-wave coupled operational system FOAM-AMM15. The AMM15SL2 baseline configuration is based on a two-tier SMC grid that focuses on the shelf seas around the United Kingdom (3km resolution) where coastal cells have 1.5km resolution and wavecurrent interaction is included. Results from a 2-year hindcast demonstrate the ability of the baseline configurations to reproduce both in-situ and satellite wave observations. Model-observations correlation is above 0.94-0.96 with standard deviations of differences that correspond to maximum 13-25% of the observed mean bulk wave diagnostics, demonstrating quality and accuracy of the system. Evidence of resolution dependent differences in wave growth was observed, leading slightly overestimated significant wave heights when replicating coastal mid-range conditions by AMM15SL2, and better suited to replicate the extremes. Additionally, the inclusion of wave-current interaction in AMM15SL2 tends to larger spread the observation-model differences. Hence, although a positive impact of the surface currents is not always shown in the overall statistics of the significant wave height, the addition of currents helps to significantly improve the prediction of the wave direction and period near the coast (>20% improvement), which has implications in beach safety, risk to coastal overtopping and shoreline evolution. Future system developments such as the use of sea point wind forcing, the optimisation the models in line with model resolution, the utilisation of SMC multigrid and data assimilation are discussed. [ABSTRACT FROM AUTHOR]

Headland bypassing is the transport of sediment around rocky headlands by wave and tidal action, associated with high-energy conditions and embayment circulation (e.g., mega-rips). Bypassing may be a key component in the sediment budget of many coastal cells, the quantification of which is required to predict the coastal response to extreme events and future coastal change. Waves, currents, and water levels were measured off the headland of a sandy, exposed, and macrotidal beach in 18-m and 26-m depths for 2 months. The observations were used to validate a Delft3D morphodynamic model, which was subsequently run for a wide range of scenarios. Three modes of bypassing were determined: (i) tidally-dominated control during low–moderate wave conditions [flux O (0–102 m3 day−1)]; (ii) combined tidal- and embayment circulation controls during moderate–high waves [O (103 m3 day−1)]; and (iii) multi-embayment circulation control during extreme waves [O (104 m3 day−1)]. A site-specific bypass parameter is introduced, which accurately (R2 = 0.95) matches the modelled bypass rates. A 5-year hindcast predicts bypassing is an order of magnitude less than observed cross-shore fluxes during extreme events, suggesting that bypassing at this site is insignificant at annual timescales. This work serves a starting point to generalise the prediction of headland bypassing. [ABSTRACT FROM AUTHOR]