What is WW3?
WAVEWATCH III (WW3) (WW3DG, 2019) is a third-generation spectral wave model that integrates the latest advances in wind–wave dynamics. Originally developed at NOAA/NCEP, it is now maintained and further developed by the international WW3 Development Group.

WW3 solves the random phase spectral action density balance equation for wavenumber-direction spectra, including advanced parameterizations for wave growth, nonlinear interactions, dissipation, and interactions with bottom topography, sea-ice, and currents. The model also offers options for shallow-water applications, including the surf zone and wet&dry areas. Wave energy spectra are discretized using a constant directional increment covering all directions and a spatially varying frequency grid.

The model can run on regular and unstructured grids, individually or combined in nested multi-grid mosaics, enabling applications from global ocean simulations to high-resolution coastal studies. Unstructured grids allow seamless cross-scale transitions and enable high-order propagation schemes in global applications. They also support implicit time-integration in shallow-water areas, permitting larger timesteps and facilitating more efficient parallel domain decomposition through advanced partitioning algorithms.

WW3 is widely used for marine weather forecasting, research, and operational services,supports parallel computing and can be coupled with other Earth system components through OASIS or ESMF/NUOPC frameworks.

WW3 is open-source and freely available, including the source code and a range of test cases for training and functionality evaluation. The latest official release is version 6.07, available on GitHub, together with comprehensive documentation and online tutorial.

How does CMCC use WW3?

WW3 is used in several operational systems and national and international projects at CMCC, covering global, regional, coastal and urban scales.

At the global level, an unstructured WW3 configuration, UGLOB (Carvalho et al. 2025, in preparation), with a coastal resolution of around 2–4 km and 50 km offshore, has been used to investigate extreme events such as Hurricane Lorenzo (developed within the EDITO project). CMCC is currently working to integrate an unstructured wave component, based on WW3 and coupled via  NUOPC, into the next version of its Earth System Model, CMCC-CM. Recently, a large ensemble of global wave climate projections has been produced with an unstructured configuration at 15 km coastal resolution and 100 km offshore, covering four SSP scenarios and ten ensemble members (five ISIMIP primary and five ISIMIP secondary models).

At the regional scale, WW3 is applied in the Mediterranean Forecasting System (MedFS, 1/24°) and the Black Sea Forecasting System (BSFS, 1/40°). Both operational systems use regular grids in coupled hydrodynamic–wave configurations to deliver oceanic medium-term forecasts (Clementi et al., 2017; Coppini et al., 2023; Ciliberti et al., 2022; Causio et al., 2021, 2024), within the framework of the Copernicus Marine Service. In the Adriatic Sea, WW3 has also been implemented on a regular grid with 1/48° spatial resolution to produce long-term hindcasts and climate projections (Moulin et al., 2024), as part of the AdriaClim and AdriaClimPlus projects, aimed at advancing scientific knowledge on climate change and its impacts in the region.

For coastal applications, CMCC has developed and implemented around 20 forecasting systems aimed at investigating coastal processes, wave–current interactions (Causio et al., 2021), extreme events (Causio et al., 2025), climate variability (Pillai et al., 2022a; Causio et al., 2024) and urban and harbour scale.

A dedicated procedure for downscaling wave spectral models has been developed to reconstruct spectra at the boundaries from standard mean wave parameters. This approach eliminates the need to run a larger parent model to provide spectral boundary conditions and emphasizes the development of relocatable nested wave models, enhancing their portability and reusability. WW3 is planned to be included soon in CMCC’s SURF platform.

In addition, CMCC has implemented new formulations in WW3 for representing vegetation effects (Pillai et al., 2022b; Shirinov et al., 2025), extending the model’s capability towards coastal-oriented processes and the assessment of Nature-Based Solutions.

Several coastal forecasting applications are operational and serve project-specific objectives, such as AdriFS, Civitavecchia, and the Gulf of Taranto systems.

References

Carvalho et al. (2025). Unstructured-grid Global Coastal Waves: a hi-resolution global model for Extreme wave events (in preparation)

Causio, S., Ciliberti, S. A., Clementi, E., Coppini, G., & Lionello, P. (2021). A modelling approach for the assessment of wave-currents interaction in the Black Sea. Journal of Marine Science and Engineering, 9, 893. https://doi.org/10.3390/jmse9080893

Causio, S., Federico, I., Jansen, E., Mentaschi, L., Ciliberti, S. A., Coppini, G., & Lionello, P. (2024). The Black Sea near-past wave climate and its variability: a hindcast study. Frontiers in Marine Science, 11, 1406855. https://doi.org/10.3389/fmars.2024.1406855

Causio, S., Shirinov, S., Federico, I., De Cillis, G., Clementi, E., Mentaschi, L., & Coppini, G. (2025). Coupling ocean currents and waves for seamless cross-scale modeling during Medicane Ianos. Ocean Science, 21(3), 1105–1123.

Ciliberti, S. A., Jansen, E., Coppini, G., Peneva, E., Azevedo, D., Causio, S., et al. (2022). The Black Sea Physics Analysis and Forecasting System within the framework of the Copernicus Marine Service. Journal of Marine Science and Engineering, 10(1), 48. https://doi.org/10.3390/jmse10010048

Clementi, E., Oddo, P., Drudi, M., Pinardi, N., Korres, G., & Grandi, A. (2017). Coupling hydrodynamic and wave models: First step and sensitivity experiments in the Mediterranean Sea. Ocean Dynamics, 67, 1293–1312. https://doi.org/10.1007/s10236-017-1087-7

Coppini, G., Clementi, E., Cossarini, G., Salon, S., Korres, G., Ravdas, M., et al. (2023). The Mediterranean Forecasting System – Part 1: Evolution and performance. Ocean Science, 19, 1483–1516. https://doi.org/10.5194/os-19-1483-2023

Moulin, A., Mentaschi, L., Clementi, E., Verri, G., & Mercogliano, P. (2024). Projections of the Adriatic wave conditions under climate changes. Front. Clim. 6:1409237. https://doi.org/10.3389/fclim.2024.1409237

Pillai, U. P. A., Pinardi, N., Alessandri, J., Federico, I., Causio, S., Unguendoli, S., Valentini, A., & Staneva, J. (2022b). A Digital Twin modelling framework for the assessment of seagrass Nature Based Solutions against storm surges. Science of the Total Environment, 847, 157603. https://doi.org/10.1016/j.scitotenv.2022.157603

Pillai, U. P. A., Pinardi, N., Federico, I., Causio, S., Trotta, F., Unguendoli, S., & Valentini, A. (2022a). Wind-wave characteristics and extremes along the Emilia-Romagna coast. Natural Hazards and Earth System Sciences, 22, 3413–3433. https://doi.org/10.5194/nhess-22-3413-2022

Shirinov, S., Federico, I., Bonamano, S., Causio, S., Biocca, N., Piermattei, V., … & Pinardi, N. (2025). Modeling wave-vegetation interactions: the impact of seagrass flexibility and seasonal variability. Natural Hazards and Earth System Sciences (proofreading).

WW3DG, T. (2019). User manual and system documentation of Wavewatch III version 6.07. NOAA NWS NCEP MMAB Tech Note, 333, 465.