Storm Surge From Hurricane Irene: 4-8 Feet of Flood Waters

Aug. 27, 2011 — -- Hurricane Irene pushed a giant storm surge -- essentially a wall of water -- out of its way as it marched up the Atlantic Coast, threatening to flood cities from Norfolk, Va., to New York to Boston

In many places, forecasters warned, the storm surge could be as destructive as the hurricane itself, flooding low-lying areas before the storm even arrives with its winds and pelting rain.

"Storm surge will raise water levels by as much as 4 to 8 feet above ground level within the hurricane warning area from the North Carolina/Virginia border northward to Cape Cod, including southern portions of the Chesapeake Bay and its tributaries," said Daniel Brown, the warning coordination meteorologist for NOAA's National Hurricane Center, in a forecast this evening.

"Near the coast, the surge will be accompanied by large, destructive, and life-threatening waves," Brown said.

Near Kill Devil Hills, N.C., on the Outer Banks of North Carolina, water in Pamlico Sound was reported as much as 13 feet above normal, though precise numbers were hard to verify.

"The Manteo Causeway was 5 feet under water by the time it was too dark to observe," said Scott Summers of local radio station WCXL. "Water is chest high at the docks in Manteo."

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A storm surge is, in its simplest terms, a bulge of water that a hurricane pushes out in all directions as it passes over the ocean. It can add several feet to the height of floodwaters created by the storm; in extreme cases, such as Hurricane Katrina in 2005, it can be more than 20 feet.

But the effect can vary tremendously from one place to another, especially along the nooks and crannies of the coast of the eastern United States. Some places may, in fact, see the eight-foot surges that NOAA warned about today; others may see very little.

Complicating matters is, of all things, the moon, whose gravity has such a powerful effect on high and low tides.

There is a new moon just after 9 p.m. on Sunday -- with the likely result that tides, shifting rhythmically, could be especially high during the daytime Sunday as the moon passes overhead.

"Higher than normal astronomical tides are occurring this weekend," Brown said. "Coastal and river flooding will be highest in areas where the peak surge occurs around the time of high tide."