Operational National-Scale 3D Hydrodynamic Forecasting for New Zealand Using SCHISM

Over the past years, Calypso Science has been developing high-resolution hydrodynamic representations of New Zealand’s coastal and shelf waters. Early work focused on a national hindcast, which provided a 3D baroclinic reconstruction of currents, temperature, salinity, and tides across the country (National data cube). Building on that work, thanks to PredictWind, we have now deployed a fully operational, national-scale forecast using SCHISM, capable of delivering hourly 3D fields of velocity, temperature, and salinity across the entire New Zealand domain.

The operational SCHISM model is defined on an unstructured horizontal grid, with high resolution in narrow sounds and channels while maintaining coarser resolution offshore, providing the necessary flexibility to capture fine-scale coastal processes without prohibitive computational cost. Vertically, the model employs a LSC grid, allowing detailed representation of stratification and baroclinic processes, critical for reproducing thermoclines, density-driven currents, and tidal interactions. Tidal forcing is included through a comprehensive set of harmonic constituents, including M2, S2, N2, K2, K1, O1, P1, Q1, MM, MF, M4, MN4, MS4 and 2N2 components, applied at the open boundaries to reproduce both elevations and tidal currents across the domain.

Daily GLORYS Copernicus analysis of 3D temperature, salinity, and velocity fields are provided at the open boundaries, while atmospheric forcing from the GFS 0.25° forecast supplies surface wind stress, solar radiation,and atmospheric pressure. Within the model, nudging is applied for temperature and salinity near the boundaries to maintain consistency with global forecast, with carefully chosen distances and strengths to avoid abrupt gradients.

Once computed, the hourly outputs are integrated into SeaScope, where users can explore temperature fields in direct comparison with real-time drifters, moorings, and coastal profilers, as well as GLORYS analysis. This allows operational forecasts to be interpreted in the context of ongoing observations, providing both validation and a consistent view of New Zealand’s complex coastal and offshore environment.