The size of the model domains considered often requires the use of relatively loose meshes (generally from 1° to 0.25°) in order to keep acceptable the computation time. A succession of nested models allows to reach finer resolutions, from the global scale to the regional scale (a few kilometers) and the local scale (a few hundred meters). Another technique to reach high resolutions at the coast while avoiding model nesting is the use of unstructured grids.

The models are regularly compared with observations made by the in-situ wave buoy networks (Cerema).

The sea state model outputs available on data.shom.fr provide, for each run, a forecasts from day D to day D+2/D+3/D+4, depending on the configuration.

At the global and regional scales, forecasts are produced by Météo-France’s global MFWAM model (GLOB01, 0.1° resolution), forced by the ARPEGE meteorological model from Météo-France. To optimize visualization, spatial downsampling is applied based on GLOB01 configuration:

- GLOB05: MFWAM model, global 0.5° resolution grid;

- EURAT01: MFWAM model, European 0.1° resolution grid;

- ANGUY01: MFWAM model, 0.1° resolution grid for Antilles-Guyane area;

- MASCA01: MFWAM model, 0.1° resolution grid for Indian Ocean area.

At coastal scales, sea state forecasts are produced using the Wavewatch III ®model (configurations developed by Shom in partnership with Météo-France):

- NORGAS-UG, MENOR-UG, ANGUY-CG and INDIEN-UG: unstructured grid from the WW3 model, with a resolution ranging from 10km offshore to 200m at the coast. On data.shom.fr, these irregular grids are reprojected onto regular grids with different resolutions: 2', 500m and 200m. The closer to the coast the area is, the more refined the resolution is (for example: NORGAS-2MIN -> MANCHE-NORD-500M -> NORMANDIE-200M). For metropolitan France, WW3 is forced by the Météo-France ARPEGE weather model; in the Antilles-Guyane and the Réunion-Mayotte areas WW3 is forced by the Météo-France AROME Outre-Mer model.