What is hurricane surge, and what contributes to the risk of deadly hurricanes?

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

According to Ken Graham, director of the National Weather Service, some parts of the coast can see storms of up to 18 feet. The National Hurricane Center considers a storm surge of three feet to be fatal.

“We have to talk about water,” Graham said at a briefing on Wednesday. “Ninety percent of your deaths in these tropical systems come from water,” he said, noting that the figure includes deaths from storm surges and rain floods.

What is a storm?

According to the NHC, a hurricane wave is an “abnormal surge of water generated by a storm”. As the storm moves towards the coast, the water is pushed to the shore and “piles up”, creating buoyancy.

If the storm is accompanied by high tide, the water level will be even higher. The combination of a storm wave and a tide is known as a storm tide.

Storm surge and precipitation both contribute to flooding during storms.

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 states that “storm surge is a very complex phenomenon” because it depends on many factors, including wind speed, forward speed of the storm, the size of the storm, the angle of approach to the coastline, and the size and characteristics. Are included. Coast.

Here’s an analysis of some of the factors, according to the NHC:

Intensity: Higher wind speeds usually mean more storm surge. However, even if a hurricane is low on the Saffir–Simpson hurricane wind scale, it can still cause devastating effects.

forward motion: The NHC said a fast moving storm in the open ocean would create more storms along the open coast. A slowing storm can produce “high and widespread storm surge inland.”

Shape: Big storms will generate more storms.

Angle of Approach: A hurricane that hits the coast vertically will have a greater storm surge than a storm that is parallel to the coast.

Width and Slope of Continental Shelf: Hurricane surges will be more likely to occur on a wide and shallow slope such as the Louisiana shoreline than on a narrow and steep slope along Miami Beach in Florida.

One of the most devastating storms in US history, Hurricane Katrina produced storm surges of 25 to 28 feet above normal tide levels in parts of the Mississippi coast and 10 to 20 feet above normal tide along the southeastern Louisiana coast. , NHC said. ,

In 2008, Hurricane Ike hit parts of the Texas coast 15 to 20 feet above normal tidal levels, which according to the NHC were considered a Category 2 hurricane when it made landfall.

Which areas are at risk of storm surge?

Storm surge is expected in all communities in the US East and Gulf Coast. The Hurricane Center said NHC’s Storm Surge Risk Maps “make it clear that storm surge is not just a coastline problem, there is a risk of storm surge in some areas several miles from the immediate coastline.”

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

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