INFLUENCE OF TYPHOON MOVING SPEED ON MAXIMUM STORM SURGE HEIGHT IN A BAY FACING THE OPEN OCEAN

Storm surges may bring catastrophic damage to coasts by the abnormal increase in sea level. In semi-enclosed, shallow water areas such as Tokyo Bay, the increase of sea level due to wind tends to be significant. Due to this characteristic, the fast-moving typhoon can be regarded as a potential candidate for possible maximum storm surge in Japan. The moving speed of Super Typhoon Vera in 1959 (i.e. 73 km/h), which caused the worst storm surge in Japan, is about two times faster than the average around Japan (Yamaguchi et al. 2020) but is typically used in storm surge simulation by parametric typhoon models (e.g. assessing the risk of storm surge inundation at coasts (MAFF and MLIT 2023), designing coastal defence structures (OCDI 2020)). However, this may not be true in bays facing the open ocean. High waves are likely to enter such bays, and storm surges due to wave setup can be predominant, meaning that fast-moving typhoons do not necessarily cause significant storm surges. The relationship between the moving speed and maximum storm surge height in such bays, however, seems not to be well studied. Therefore, the authors examined this relationship through the hindcast of storm surges induced by super Typhon Jebi in 2018 and numerical experiments. Typhoon Jebi brought catastrophic damages to the coastal areas of the Kansai region (Mori et al. 2019).