Thursday, June 29, 2006

Storm surge

A storm surge is an onshore rush of water associated with a low pressure weather system, typically a tropical cyclone. Storm surge is caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea level. Low pressure at the center of a weather system also has a small secondary effect, as can the bathymetry of the body of water. It is this combined effect of low pressure and persistent wind over a shallow water body which is the most common cause of storm surge flooding problems.

Storm surges are particularly damaging when they occur at the time of a high tide, combining the effects of the surge and the tide. This increases the difficulty of predicting the magnitude of a storm surge since it requires weather forecasts to be accurate to within a few hours.The most extreme storm surge events occur as a result of extreme weather systems, such as tropical cyclones, but storm surges can also be produced by less powerful storms.

Nine out of ten people who die in hurricanes are killed by storm surges. The Galveston Hurricane of 1900, a category 4 hurricane that struck Galveston, Texas on 8 September, drove a devastating surge ashore; between 6,000 and 12,000 lives were lost, making it the deadliest natural disaster ever to strike the United States (Hebert, 1990). The second deadliest natural disaster in the U.S. was the storm surge from Lake Okeechobee in the 1928 Okeechobee Hurricane which swept across the Florida Peninsula during the night of September 16. The lake surged over its southern bank, virtually wiping out the settlements on its south shore. The estimated death toll was over 2500; many of the bodies were never found. Only two years earlier, a storm surge from the Great Miami Hurricane of September 1926 broke through the small earthen dike rimming the lake's western shore, killing 150 people at Moore Haven (Will, 1978).

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