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The actions of wind and atmospheric pressure associated with tropical cyclones (e.g. typhoons) are considered the primary factors behind the generation of storm surges, though the fields used in meteorological models can sometimes deviate from observations. To improve these, the direct modification method (DMM) has been previously proposed, though this only modifies the wind field of a typhoon, and further development is necessary for applying it to storm surge hindcasts. The present work describes the development of a semi-empirical gradient wind balance-based method (GWB-M) for modifying both the wind and pressure fields in meteorological models, based on the dynamic relationship between the wind and pressure in typhoons (i.e. gradient wind balance). The applicability of GWB-M was assessed through a storm surge hindcast based on Typhoon Faxai in 2019, which generated powerful waves and a storm surge at Tokyo Bay. GWB-M improved the time series of 10 m wind speed and sea level pressure, with their spatial distributions being more realistic than those in DMM and blending parametric typhoon models (BM), which cannot take into account the influence of the complex topography around Tokyo Bay. Further, the maximum sea level anomalies after the typhoon made landfall were also captured by GWB-M with a higher accuracy than DMM. [ABSTRACT FROM AUTHOR]

A field survey of Fukuura Coast (in Tokyo Bay, Japan) revealed during the passage of Typhoon Faxai in 2019 waves with considerable momentum caused significant wave overtopping, resulting in structural damage to coastal defenses and localized flooding. The hindcasted wave height using a third-generation wave model was not high enough to explain the extent of the local damage at Fukuura Coast, likely due to such methods failing to take into account the strong gust-winds recorded during the passage of the typhoon. To solve such problems the authors developed a new numerical model that takes into account the dynamic interaction of air and water, based on the finite volume method (FVM) and the volume of fluid method (VOF). Although this model still slightly underestimates the measurements in the experiments previously conducted by different authors, it is better than existing methods when estimating the overtopping rates under strong winds. The model was then applied to a real-scale model of Fukuura Coast, where by taking into account strong gust-wind speed of 41 m/s the authors were able to explain the phenomena that took place. [ABSTRACT FROM AUTHOR]

The object of the present study is to numerically evaluate the characteristics of future potential typhoons and storm surges around Tokyo Bay under a RCP8.5 scenario usinga simple one-way model system composed of ARW-WRF and FVCO. In order to evaluate the effect of the expected future increase in sea surface temperature (SST), air temperature (AT) and relative humidity (RH) four types of cases were considered in the 2041–2060 and 2081–2100 horizons. The results show how higher SST will likely lead to more intense typhoons and storm surges, though higher AT in troposphere and tropopause will somehow moderate this effect. In addition, a simple method to estimate the most influential wind direction that can generate surge elevations in Yokohama, Tokyo and Funabashi was examined by using the results of a numerical simulation. Finally, a simple methodology to calculate the required design height of sea walls and dykes in Tokyo Bay was developed, which shows how current design levels will be insufficient to maintain the present acceptable risk levels in the area. [ABSTRACT FROM AUTHOR]