Weather Blog

What is a hurricane's "storm surge"?

What is a hurricane's "storm surge"?
You've been hearing the term a lot with Hurricane Gustav tearing into Louisiana. While wind usually grabs the headlines with hurricanes, it's the "storm surge" that can do the most damage.

The surge is just basically what happens when you blow a lot of water in one direction.  When the hurricane is out in the water, you have those 100+ mph winds pushing the water in the same direction the wind is blowing.  The stronger the wind, the greater the surge potential. You can see this by getting a big glass of water -- blow really hard on the surface and watch the water get pushed up against the far edge of the glass.

This surge of water is carried along with the hurricane, but in the open sea, the water has a change to spread out a bit under the storm since there are no constrictions. But when the storm nears land, the water is pushed ashore -- sometimes catastrophically, and almost like a localized tsunami.

It was a storm surge of 25 feet or so with Hurricane Katrina that did the vast majority of the damage -- the water overwhelmed New Orleans' levies and pushed a wall of water very far inland along the Mississippi and Alabama coast.

The surge is greatest on the eastern edge of the storm. That's because the way the hurricane spins -- counterclockwise -- that is the side of the storm with the strong south winds that push the water ahead of the storm.  On the west side of the storm, you have north winds which push the water away from the coastline and that actually greatly mitigates storm surge problems.

The eastern edge of the storm is also the stronger side, helping to enhance storm surge potential.

(I should also add that the storm surge is also aided a bit by the storm's intense low pressure at its center. That pulls water toward the center of the storm and adds a bit to the depth of the surge.)

With Gustav, the storm surge was expected to be between 8-14 feet, so not as bad as Katrina.