Friday, October 11, 2013

What is Storm Surge?

With the hurricane approaching India, I've seen a number of people ask about "storm surge." I thought this illustration would be helpful.

The line at bottom labeled "mean sea level" is the normal height of the water. If there happens to be a two-foot astronomical tide at the time of the storm surge, the water will rise by that height. In this example, the storm surge is 15 feet. That would bring the total height to 17 ft. Then, there are the waves. Let's say the waves are an extra 5 ft. So,

2' tide + 15' surge + 5' waves = water reaching 22 ft. above sea level. 

A record storm surge is predicted to occur along the northeast India coast. Some are predicting it will be as much as 20 ft. (to which tide and waves must be added).

From Eric Holthaus:

In India and Bangladesh, where so many live only a few meters above sea level, the sheer size of Phailin nearly guarantees that hundreds of thousands of homes will be inundated. A storm surge of 1 to 3 meters could extend for hundreds of kilometers northeast of where the storm makes landfall. In short, Phailin is a humanitarian disaster in the making.

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