The response of Georges Bank to the passage of Hurricane Edouard

Abstract

On September 2, 1996, Hurricane Edouard passed directly over Georges Bank moving generally northeastward. The center of the hurricane passed close to an instrumented mooring site (SF) located on the southern flank of the bank at 76 m. High winds were observed at SF over a 2.5-day period. The maximum wind speed at the SF site at 3 m above the sea level was about 22 m/s, which corresponded to a surface stress of about 1.5 Pa. This occurred just prior to the rapid veering of the wind as the center of the hurricane passed. The net surface heat flux at SF decreased to about 27 W/m 2, primarily due to the reduced solar radiation through the hurricane cloud cover. The maximum wind-forced currents observed at SF due to Hurricane Edouard were about 50 cm/s, as large as the dominant semidiurnal tidal flow. A 35-m-deep mixed layer at SF was created as the hurricane approached, which then varied between 15 and 45 m deep until restratification began on September 4. The evolution of this mixed layer was complex due to the spatially varying stratification in this region and its advection past the mooring site by the tidal- and subtidal-frequency flows. The initial forcing of the baroclinic wake appeared to be present in the detided currents as strong opposing on- and off-bank flows of the upper and lower layers observed immediately after the center of the hurricane had passed. However, this flow quickly decayed and the near-inertial waves of the baroclinic wake, generally observed in the deep ocean, were not present. We suggest that the lack of any distinct baroclinic wake and the rapid decay of the hurricane-driven flows were due to the high-frictional damping, which occurred over Georges Bank due to its shallow topography and strong tidal currents.