Hindcast

A hindcast is a model run that reconstructs past conditions by forcing the model with observed inputs over a historical period, then compared against observations the model did not assimilate to measure skill. Wave hindcasts force a spectral wave model with reanalysis winds (for example ERA5) to build multi-decadal wave climatologies for design and route studies. Seasonal and decadal forecast systems are validated by retrospective hindcasts before operational use. A hindcast differs from a reanalysis: a reanalysis assimilates the observations, while a free-running hindcast uses them only as forcing and as the verification target.