What is a storm surge?

As a hurricane approaches the coast, swirling winds push ocean water onto land; The storm’s atmospheric pressure also helps push water onto land. The shallower the continental shelf, the greater the threat of a dangerous wave. It may take a few days for the water to recede completely.

Water is heavy – about 770 kg to a cubic meter (0.76 cubic meters) – and it can move quickly in a wave, sweeping people to their deaths, overturning boats and vehicles and crushing structures. Eight inches of fast-moving water is enough to knock over an adult, the National Hurricane Center (NHC) says. Floods become even more dangerous as they coincide with high tides.

Hurricane Katrina caused storm surges of more than 25 feet on the Mississippi coast in 2005. The NHC says many of the 1,500 people who died died directly or indirectly as a result of the storm surges.

What will be the impact of Hurricane Milton?

Storm surge is often the greatest threat to life and property from a hurricane, according to the National Weather Service, which added that in the past, large death tolls from major hurricanes have often resulted from the rise of the ocean.

The National Weather Service is expecting life-threatening storm surges along Florida’s Gulf Coast this week, with storm surge as high as 8 to 10 feet above ground level forecast in some areas.

On Monday, officials in Sarasota County, Florida, issued evacuation orders and said the forecast storm surge there from Milton will be double that of Hurricane Helene.

Experts in Sarasota are predicting a storm surge of 10 to 12 feet for the area, which they say would be unsurvivable on the barrier islands.

According to the National Oceanic and Atmospheric Administration (Noaa), hurricane storms can cause extensive damage, “severely erode beaches and coastal highways” and destroy boats and buildings.

“If waters move inland, rivers and lakes could be affected, which could exacerbate rising flood rates,” the government said.

In 2022, Hurricane Ian caused catastrophic storm surge along the southwest and northeast coasts of Florida. In some areas the storm surge was as high as 5 meters.

How is the climate crisis a factor?

Because greenhouse gases help trap heat in the atmosphere, they also help charge the oceans with record temperatures. The heat in the Gulf of Mexico, where many of these storms develop, has been abnormally high and this extra heat acts as a kind of jet fuel for hurricanes, quickly turning them into major storms.

Researchers have found that since the 1970s, the number of storms escalating into Category 4 or 5 hurricanes, with winds of at least 130 miles per hour, has roughly doubled in the North Atlantic. “If you look back in time, storms have historically increased more slowly than they do today,” said Phil Klotzbach, a researcher at Colorado State University who specializes in hurricane forecasts.

What will the long-term costs be?

The costs of extreme weather due to the climate crisis continue to rise. Last year there were a record 28 disasters in the US, each costing at least $1 billion.

In the wake of Hurricane Helene, an estimate from private forecaster AccuWeather said damage could be between $225 billion and $250 billion.