What is a hurricane storm surge, and why is it so dangerous?

Of all the hazards that hurricanes bring, storm surge is the biggest menace to everyday living and assets alongside the coastline. It can sweep homes off their foundations, flood riverside communities miles inland, and break up dunes and levees that usually safeguard coastal areas from storms.

This week, forecasters had been warning yet again about the potential for a daily life-threatening storm surge as Hurricane Sally headed toward Louisiana.

But what precisely is storm surge?

What storm surge appears to be like like from shore

As a hurricane reaches the coast, it pushes a substantial volume of ocean drinking water ashore. This is what we get in touch with storm surge.

This surge seems as a gradual increase in the h2o stage as the storm approaches. Dependent on the dimensions and track of the hurricane, storm surge flooding can very last for many hrs. It then recedes right after the storm passes.

Water stage heights all through a hurricane can attain 20 feet or much more above normal sea level. With strong waves on leading of it, a hurricane’s storm surge can result in catastrophic harm.

What establishes how high a storm surge receives?

Storm surge commences more than the open up ocean. The strong winds of a hurricane push the ocean waters all around and result in h2o to pile up beneath the storm. The low air pressure of the storm also performs a compact role in lifting the water degree. The height and extent of this pile of drinking water depend on the power and measurement of the hurricane.

As this pile of h2o moves towards the coastline, other aspects can transform its peak and extent.


The depth of the sea flooring is a single issue.

If a coastal spot has a sea ground that carefully slopes away from the coastline, it is a lot more probable to see a better storm surge than an region with a steeper fall-off. Mild slopes alongside the Louisiana and Texas coasts have contributed to some devastating storm surges. Hurricane Katrina’s surge in 2005 broke levees and flooded New Orleans. Hurricane Ike’s 15- to 17-foot storm surge and waves swept hundreds of houses off Texas’ Bolivar Peninsula in 2008. Both were being significant, effective storms that hit in vulnerable destinations.

The shape of the coastline can also form the surge. When a storm surge enters a bay or river, the geography of the land can act as a funnel, sending the water even bigger.

Other variables that shape storm surge

Ocean tides – brought on by the gravity of the moon and sun – can also reinforce or weaken the impression of a storm surge. So, it is crucial to know the timing of the regional tides compared to the hurricane landfall.

At high tide, the h2o is now at an elevated top. If landfall takes place at higher tide, the storm surge will bring about even higher drinking water degrees and carry far more drinking water even more inland. The Carolinas saw people consequences when Hurricane Isaias hit at close to high tide on Aug. 3. Isaias brought a storm surge of about 4 ft at Myrtle Beach, South Carolina, but the water level was far more than 10 ft higher than ordinary.

How a storm surge and significant tide include up to coastal flooding.
The COMET Plan/UCAR and Countrywide Weather Services

Sea degree rise is an additional growing concern that influences storm surge.

As drinking water warms, it expands, and that has slowly lifted sea level as world temperatures have risen since the begin of the industrial period. Freshwater from melting of ice sheets and glaciers also adds to sea stage rise. With each other, they elevate the qualifications ocean height. When a hurricane comes, the larger ocean suggests storm surge can bring water even more inland, to a a lot more unsafe and popular result.

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