The development of a numerical wave prediction model incorporating a parametrical wind-sea model and a characteristic swell model is described. The parametrical model is an extension of an earlier two-parameter model to the full five Jonswap spectral parameters. An application is presented in which the model is used to hindeast severe wave conditions in the North Sea as part of an engineering study to define long-term extreme wave statistics for the area. The limitations of the model and the needs for future research are discussed.