A storm surge or tidal surge is an offshore rise 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. The term "storm surge" in casual (non-scientific) use is storm tide; that is, it refers to the rise of water associated with the storm, plus tide, wave run-up, and freshwater flooding. When referencing storm surge height, it is important to clarify the usage, as well as the reference point. National Hurricane Center tropical cyclone reports reference storm surge as water height above predicted astronomical tide level, and storm tide as water height above NGVD-29.

In areas where there is a significant difference between low tide and high tide, storm surges are particularly damaging when they occur at the time of a high tide. In these cases, 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. Storm surges can be produced by extratropical cyclones, such as the "Halloween Storm" of 1991 and the Storm of the Century (1993), but the most extreme storm surge events occur as a result of tropical cyclones. Factors that determine the surge heights for landfalling tropical cyclones include the speed, intensity, size of the radius of maximum winds (RMW), radius of the wind fields, angle of the track relative to the coastline, the physical characteristics of the coastline and the bathymetry of the water offshore. The SLOSH (Sea, Lake, and Overland Surges from Hurricanes) model is used to simulate surge from tropical cyclones. The Galveston Hurricane of 1900, a Category 4 hurricane that struck Galveston, Texas, drove a devastating surge ashore; between 6,000 and 12,000 lives were lost, making it the deadliest natural disaster ever to impact 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 2,500; 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, Florida (Will, 1978). The storm surge that accompanied the New England Hurricane of 1938 killed as many as 700 people when it hit Long Island, New York and southeastern New England.