Local and Remote Storm Surge Contributions to Total Water Levels in the Gulf of St. Lawrence During Hurricane Fiona

Post-tropical Hurricane Fiona generated a large storm surge that resulted in pronounced flooding and coastal erosion in Atlantic Canada in September 2022. In this study we apply a regional barotropic storm surge model in the Gulf of St. Lawrence, a semi-enclosed sea, to demonstrate a method of evaluating different contributions to the total water levels. These include the surge generated over the ocean, the surge generated by the cyclonic winds over the gulf, and the tides. The results indicate that the highest storm surge occurred in the southeastern region, a combination of locally and remotely generated components. The surge that entered from the ocean was greater than the surge generated over the gulf; however, these were not in phase. To investigate the case where the local and remote surges are coincident, we shift the wind field relative to the timing of the boundary conditions and find the near "perfect storm" with significantly higher storm surge elevations. These findings highlight the importance of basin morphology and storm conditions in controlling the interactions of surge components, and this approach can be applied to simulate a range of storm-driven hazard outcomes for future extreme events.