The environmental impact assessment is becoming very important with increased public awareness to the environmental issues. In many cases, future conditions of water environment are evaluated referring to the results obtained from numerical simulations that are carried out based on the possible scenario. However, it is quite difficult to set some computational conditions in detail. In this study, to predict the tidal currents at coastal area, firstly, the numerical simulation model has been developed. This model was calibrated using global optimization technique named ACCO. Its accuracy of predicted result related to the tidal motion in Shimabara Bay was shown. Following, the tidal current simulation was curried out using weather data forecasted by mesoscale model, MSM. The calculated results show that the tidal motion of this bay is changed strongly affected by the wind blowing on the water surface, and temporal and spatial variation of meteorological condition should be adequately taken into account for the precise prediction of material transportation. Furthermore, from the results obtained by simulations regarding the uncertainty of forecasted weather data, it seems that uncertainty analysis will be required to evaluate the accuracy of predicted results.