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Hurricane storm surge 

While hurricanes are associated with high winds that can cause significant damage, the most dangerous and damaging characteristic of a hurricane is its ability to create what is called storm surge.

Diagram courtesy of NOAA

Storm surge is simply water that is pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level 15 feet or more. In addition, wind driven waves are superimposed on the storm tide. This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Because much of the United States' densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level, the danger from storm tides is tremendous.

Storm surge damage from Katrina. Photo courtesy of Army Corps of Engineers.

Wave and current action associated with the tide also causes extensive damage. Water weighs approximately 1,700 pounds per cubic yard; extended pounding by frequent waves can demolish any structure not specifically designed to withstand such forces. The currents created by the tide combine with the action of the waves to severely erode beaches and coastal highways. Many buildings withstand hurricane force winds until their foundations, undermined by erosion, are weakened and fail.In estuaries and bayous, intrusions of salt water endanger the public health and send animals, such as snakes, to flee from flooded areas and take refuge in urban areas.

Hurricanes often also spawn tornadoes, which create additional and substantial damage.

For more on hurricanes, go here: www.nhc.noaa.gov/HAW2/english/intro.shtml