Attribution of extreme winds during 2022 post-tropical cyclone Fiona in Atlantic Canada

Hurricane Fiona, which made landfall as a post-tropical cyclone in Atlantic Canada, on the 24th of September 2022, became the costliest natural disaster in Atlantic Canada causing $900 million in insured losses in the region. Fiona set the new Canadian record for the lowest atmospheric pressure ever recorded on land, and caused extensive wind damage and coastal flooding, driven by large waves and destructive storm surge. In this study, we show that the maximum wind speeds observed on the 24th of September 2022 were roughly a once-in-a-century event for the hurricane season in Atlantic Canada, based on the ERA5 reanalysis data. Using the wind speed data obtained from HighResMIP (High Resolution Model Intercomparison Project) simulations, we assess whether human-caused climate change has influenced the probability of extreme winds comparable to those observed in Atlantic Canada following Fiona's landfall. We find that differences in how daily mean wind speed is derived across the CMIP6 models prevent this variable from being combined into a multi-model ensemble. Instead, we use daily maximum wind speed, which is more consistently derived. Our analysis indicates that HighResMIP models simulate a statistically significant increase in the likelihood of maximum wind speeds during the hurricane season (June-October) in Atlantic Canada in the current climate compared to the climate of 1950-1979.