On both occasions, tropical storms moved rapidly across the Grand Banks of Newfoundland, with a translation speed of approximately 30 m/s. A significant, non-isostatic response to atmospheric pressure forcing can be expected over the shallow water of the Banks, since the translation speed of the storms is comparable to the local shallow water gravity wave speed. We speculate that the atmospheric pressure forcing associated with the storms generated a barotropic wake, and use a numerical model to argue that as the storm moved back over the deep ocean, the wake was refracted and/or reflected by the variable bathymetry at the edge of the Banks, and that it was the refraction of the wake towards the coast that led to the unusual sea level events in southeastern Newfoundland.
The numerical model results are in general agreement with the eyewitness reports. The model-computed wave activity hits the southeast coast of Newfoundland at about the right time and in the right areas for both events, although for the 1999 event the model response is weaker than observed at one location. The reason for the poorer model performance in the 1999 case is not known, although we do find that the model results are sensitive to uncertainty in the exact track taken by the storm across the Banks. The model results demonstrate that the period and wavelength of the gravity waves comprising the wake are, in general, proportional to the length scale of the pressure forcing, an exception being the model response in Conception Bay, Newfoundland, where a resonant seiche response is found to dominate.
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