What is Storm Surge?
Storm surge is the abnormal rise in sea level generated by a hurricane or other intense storm, over and above the predicted or normal astronomical tide. It is caused mainly by hurricane winds shoving the ocean water up over the coast, although low pressure in the eye also contributes a much smaller amount.
The height of water level rise due to storm surge is the difference at the coast between the observed level of the sea surface and the level that would have occurred in the absence of the tropical cyclone. So, as shown in the example below, the storm surge at the coast would be 20 feet (6 m) above normal tide levels. As the elevation increases, the depth of the water decreases, but land areas up to 20 feet in elevation (in this case) would be vulnerable to flooding.
"Storm tide" is the water level rise due to the combination of the storm surge and the astronomical tide, so water levels will be especially high when the storm surge occurs at the same time as high tide. As an example, during Hurricane Katrina (2005) the storm tide along the Mississippi coast was higher than 20 feet in most places, and the water was able to penetrate inland as far as 6 to 12 miles from the coast.
As the surge comes in, prior to the eye making landfall, the rising water often acts as a "bulldozer", destroying homes and leveling property along the coast. Beaches, cars, trees, and anything in the path of the rising water are washed away. Low lying areas are inundated and severe flooding occurs as the water from the ocean travels inland.
Beach erosion and destroyed seawall in Florida after Hurricane Jeanne (2004)