Generally a wave model and a storm surge model have been conducted independently, however the wave height and the storm surge in west Suo-nada Bay by Typhoon 9918 might be underestimated by neglect of the interaction between wave and current as well as the underestimation of the marine wind speeds.
　For such a background, in this study the wave model (WAM cycle 4) is improved to take water surface elevations and currents of astronomical and meteorological tides into the calculation of wave generation and refraction. On the other hand, the storm surge model based on the non-liner long wave theory is improved to introduce the surface friction coefficients in the wave model and astronomical tides into the calculation of storm surges. Then the wave model and the storm surge model are mutually combined each other. The marine wind for the combined model is estimated by considering the distortion of typhoon pressure field and the existence of super gradient wind.
　The waves and the storm surges in Suo-nada and Yatsushiro-kai Bays by Typhoon 9918 are hindcasted by the combined model. The wave height may increase by the rise of the water level in their shallow regions, while the surface friction coefficients in the wave model may affect the storm surge in their innermost regions. Therefore, the mutual interaction between wave and current should be taken into the estimation of waves and storm surges in closed bays.