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Explainer: What is 'storm surge'

Explainer: What is 'storm surge'
Posted at 3:11 PM, Aug 26, 2020
and last updated 2020-08-26 15:11:34-04

Hurricane Laura is expected to create an “unsurvivable storm surge,” of up to 15 feet in some places, according to the National Hurricane Center.

Here is an explanation of what storm surge is, and why it can be so deadly.

“Storm surge is the rise in seawater level caused solely by a storm,” says NOAA. It is measured as the height of the water above the “normal predicted astronomical tide,” caused by the storm’s winds pushing water onshore.

A “storm tide” is the total observed water level during a storm that includes storm surge and astronomical tide. Astronomical tides are caused by the gravitational pull of the sun and moon.

According to NOAA, the National Oceanic and Atmospheric Administration, the highest storm tides are often observed during storms that coincide with a new or full moon.

storm surge graphic
A graphic showing storm surge.

Although many coastlines have barriers in place to protect against high tide or even small surges, a major hurricane can bring storm surges of several feet.

This can send waves of water into coastal towns, washing out roads, buildings and other infrastructure.

The NHC says that many of the deaths from Hurricane Katrina, which made landfall in Louisiana in 2005, were the direct or indirect result of storm surge.