How Does a Storm Surge Form?

Formation

Hurricane winds are extremely powerful. Sometimes, gusts of wind can reach speeds of 190 mph. These forceful winds move in a circular pattern and push on the water much like the winds that generate the waves breaking on a beach. On the ocean side of the storm, the water can flow "downhill" and thus, any increase in sea level is minimal. The landward side, however, is a different story. As the hurricane approaches land, the wind piles the water into a hill, just ahead of the eye of the storm.

The storm surge is created by hurricane winds, but the shape of the coastline also helps to determine its height. A steeper slope and narrower continental shelf allow the water in the mound to dissipate to a greater degree, whereas a shallower slope and broader continental shelf encourage the formation of larger surges. The Gulf Coast of the United States features shallower slopes along its coastline, so it is more likely to see large storm surges than deep-water coastlines.

Another important consideration is the tide. If the arrival of the storm surge happens at or near high tide, the sea level is even greater still. The combination of the normal high tide and the storm surge is called the storm tide. Storm surges also tend to be stronger near the right of the eye, because the winds in the hurricane move in a circular pattern. To the right of the eye, they blow directly toward the shore, so they tend to pile up more water here. To the left of the eye, on the other hand, they blow away from the shore.

When Hurricane Katrina hit New Orleans in 2005, it came along with storm surges ranging from 25 to 28 feet. Large storm surges like these cause serious flooding and damage. They bring violent hurricane waves in contact with structures not designed to withstand them, and they can erode foundations below buildings, roads and other structures. By flooding coastal land and estuaries, they can also introduce large quantities of seawater into sensitive ecosystems, causing damage not only to human life and property but wildlife as well.