Unexpected meteotsunamis prior to Typhoon Wipha and Typhoon Neoguri

Two meteotsunamis were unexpectedly observed along the eastern coast of Japan coincidentally with atmospheric pressure disturbances prior to two typhoons, respectively. The maximum wave height of meteotsunamis was up to ~ 0.5 m in Aburatsubo Bay with the pressure fluctuation of ~ 2 hPa before Typhoon Wipha. This study reveals the causes of the unexpected meteotsunamis in association with atmospheric forcings of the typhoons. The possible origin is identified from typhoon activities at the outer circulation that produced traveling pressure disturbances as a driving force to generate meteotsunamis. The causality of meteotsunamis is revealed by time–frequency analysis of sea level, atmospheric pressure, and wind speed. Results show that a combination of atmospheric forcings, pressure and wind stress, is responsible for the onset of meteotsunamis. The pressure fluctuation is found to be an indicator to determine the origin of atmospheric forcings and the formation of corresponding meteotsunamis when the meteorological condition is relatively calm before a typhoon.