Basin-constrained Hurricane Wave Growth: Simulation of Post-tropical Hurricane Fiona Over the Gulf of St. Lawrence

Post-tropical Hurricane Fiona (2022) crossed the Gulf of St. Lawrence in Atlantic Canada, generating large waves and strong wave-driven currents in this semi-enclosed coastal sea. In this study, surface waves and circulation conditions were simulated using a dynamically coupled wave-circulation model revealing significant wave heights Hs ≤ 9.4 m and current speeds >1.0 m s−1. Good agreement was obtained for bulk wave statistics (r2 > 0.86 for Hs), and broad-scale validation was achieved over a large area using observations from seven satellite altimeters. Higher resolution modelling of wind-generated waves in Malpeque Bay, a back-barrier bay connected to the Gulf, used a nested grid to simulate the waves in sheltered areas with short fetch. Significant wave heights ≤ 2.2 m in back-barrier regions, and current speeds ≤ 1.5 m s−1 in coastal areas around the barrier islands were simulated. Limitations to wind-wave growth were examined through comparison of stationary and nonstationary simulations (time constraints) and analysis of the ratio of storm translational speed to wave celerity (spatial constraints). The results indicate that despite extreme winds, the wave field remained dominated by locally generated young wind sea. Because the storm footprint was comparable to the horizontal basin scale, translating-fetch resonance and sustained swell development were spatially constrained and stationary simulations overpredicted peak wave heights (by up to ∼25%) under rapidly evolving wind conditions. These findings demonstrate how basin geometry can fundamentally limit hurricane wave growth in marginal seas, even during extreme events.