Though Hurricane Irene’s winds weakened slightly, to 75 knots, as the storm passed over North Carolina’s Outer Banks, the destructive power of Irene’s storm surge is already coming into full view. For Rhode Islanders, understanding the dynamics of storm surges is of particular interest, as the latest forecasts call for an up to eight-foot storm surge in parts of Narragansett Bay and Buzzards Bay. Coming on top of already higher than average tides on Saturday, August 27, and Sunday, August 28, the surge could lead to water levels of three to five feet above ground level.
A storm surge is created when a hurricane’s winds literally blow water onto the shore and create an abnormal rise in the water level above predicted astronomical tides (the storm’s low atmospheric pressure also contributes slightly to storm surge, though it only accounts for about 5 percent of the rise). When the height of the storm surge is added to the astronomical tides, the total is referred to as the storm tide.
The topography of the coast has a significant impact on the size of the storm surge. A shallow slope will produce a greater storm surge than a steep shelf, while a steeper slope will see less storm surge. In the case of Hurricane Irene, current predictions are for more significant storm surges along the coasts of Rhode Island and Massachusetts than along the Maine coast, which has a steeper coastal shelf than southern New England and is currently predicted to see a one- or two-foot storm surge. Regardless, any storm surge is likely to produce significant coastal erosion and lead to significant property damage along the coast. (In Hurricane Katrina, the 25- to 28-foot storm surge was what produced much of the destruction in New Orleans.)
For the latest watches, warnings and advisories for Rhode Island, click here.
For a graphic explanation of storm surge, click here.
For the latest updates on Hurricane Irene, click here.