What is a storm surge and what contributes to the deadly danger of hurricanes?

One of the most dangerous and deadly hazards of a hurricane is storm surge. How Hurricane Jan hit Florida’s west coast, FEMA warned it was expected to cause “life-threatening storm surge and widespread flooding.”

Some parts of the coast could see a storm surge of up to 18 feet, according to Ken Graham, director of the National Weather Service. The National Hurricane Center considers a storm surge of three feet to be life-threatening.

“We have to talk about water,” Graham said at a briefing Wednesday. “Ninety percent of all deaths in these tropical systems are from water,” he added, noting that this figure includes deaths from storm surge and flooding.

What is a storm surge?

A storm surge is an “abnormal rise of water caused by a storm” according to the NHC. As the storm moves toward the coast, water is pushed ashore and “builds up,” creating a surge.

If a storm surge occurs at the same time as high tide, the water level will be even higher. The combination of a storm surge and a high tide is known as a storm surge.

Storm surge and precipitation contribute to flooding during a hurricane.

A 15-foot storm surge combined with a 2-foot high tide creates a 17-foot storm surge.

NOAA/COMET Program


What factors contribute to storm surge?

The NHC says that “storm surge is a very complex phenomenon” because it depends on a number of factors, including wind speed, storm speed, storm size, angle of approach to the coastline, and the shape and characteristics of the storm. coast.

Here’s a breakdown of some of the factors according to the NHC:

Intensity: Higher wind speeds usually mean higher storm surge. However, even if a storm is below the Saffir-Simpson Hurricane Wind Scale, it can still cause devastating effects.

Forward speed: A storm moving quickly over the open ocean will produce more storm surge along the open coast, the NHC said. A slower-moving storm could create a “higher and wider storm surge inland.”

Size: Stronger storms will result in more storm surge.

Angle of approach: A storm making landfall perpendicular to the coast will have a larger storm surge than a storm passing parallel to the coast.

Width and slope of the continental shelf: Storm surge is likely to be greater over a broad, shallow slope, such as the Louisiana coast, than over a narrow, steep slope, such as along Miami Beach, Florida.

Hurricane Katrina, one of the most destructive storms in U.S. history, produced a storm surge of 25 to 28 feet above normal tide levels along the Mississippi coast and 10 to 20 feet above normal tide levels along the southeast Louisiana coast, the NHC said. .

In 2008, parts of the Texas coast received storm surges 15 to 20 feet above normal high tide levels from Hurricane Ike, which was considered a Category 2 storm when it made landfall, according to the NHC.

What areas are at risk of storm surge?

Communities along the eastern US and Gulf Coast are vulnerable to storm surge. NHC Storm surge risk maps “Make it clear that storm surge is not just a problem at the beach, in some areas the storm surge risk extends many miles inland from the immediate coastline,” the hurricane center said.

Risk maps are also provided for Puerto Rico, Hawaii, and Southern California.

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