Triple jeopardy: The Tonga tsunami, a storm surge, and a meteotsunami simultaneously hit the US East Coast on 16-17 January 2022

The eruption of the Tonga–Hunga underwater volcano in the Central Pacific on 15 January 2022 generated pronounced atmospheric pressure waves that circumvented the globe several times during the next five days. Propagating with a sound speed of ~10 spherical degrees/hour, the pressure waves forced substantial tsunami waves in the Atlantic Ocean that impacted the East Coast of the United States. Almost simultaneously, on 16-17 January 2022, a deep midlatitude cyclone crossed the East Coast. The cyclone, which formed over the northern part of the Gulf of Mexico, began to rapidly intensify as it moved northward. When it reached 40° N, the system produced a pressure change of 36 hPa/24 hours, classifying the cyclone as a “bomb cyclone”. Strong high-frequency (period <4 h) atmospheric pressure disturbances accompanied the cyclone. Both the large-scale atmospheric low and the markedly enhanced pressure disturbance reached their full strengths during the early morning of 17 January 2022 in the proximity of Atlantic City. As a consequence, three hazardous events - storm surge caused by the midlatitude cyclone, a tsunami caused by the Tonga air pressure waves and a meteotsunami caused by the HF atmospheric pressure disturbance struck the US East Coast on 16-17 January 2022, producing cumulative devastating effects in the coastal zone. Severe coastal flooding affected the Atlantic City region, where sea level heights were increased by as much as 150 cm. This unique joint event is examined in detail and the properties of the atmospheric processes and associated sea level response are thoroughly analysed. The contributions from the various sea level components are assessed and their interaction evaluated.