An operational regional wave forecasting system has been established to fulfill the demands of maritime engineering applications in the northeastern coast of Taiwan. The man-machine mix system is used to obtain valid forecasts. This system consists of sophisticated numerical models and moreover, experienced marine meteorologists are located at the construction site as the predictors to improve the forecasting accuracy. The aim of this paper lays on investigation of the role of in-situ predictors. In present paper, yearly records of daily forecasts that issued by predictors as well as the direct outputs from numerical models are used as the data base for comparative study. The issue of how much would the performance of the whole system be benefited from in-situ predictors will be discussed. These information could give us hints on the shortcomings as well as the direction of further improvement of present operational numerical wave models.