As a hurricane’s winds spiral around and around the storm, they push seawater into a mound at the storm’s center. This mound of water becomes dangerous when the storm reaches land because it causes flooding along the coast. The water piles up, unable to escape anywhere but onto land as the storm moves towards the shore. A hurricane will cause more storm surge in areas where the ocean floor slopes gradually.
When high tide happens at the same time as a storm surge, the combination of the two is called storm tide. During a storm tide, the water level may be 20 feet or more above normal. This causes huge floods. Storm tide is especially dangerous for flat islands or coastal areas where the land is not much higher than sea level.
There are computer models that allow forecasters to predict the amount of storm surge that will affect a coastal area. A model called SLOSH takes into account a storm’s strength, its path, how the ocean shallows, and the shape of the land and calculates how much storm surge a hurricane will probably cause.