What is a storm surge and what danger does Hurricane Milton pose? | Hurricane Helene

What is a storm surge?

When a hurricane approaches a coast, the turbulent winds push seawater onto land; The storm's atmospheric pressure also helps push the water onto land. The flatter the continental shelf, the greater the risk of dangerous flooding. It may take a few days for the water to subside completely.

Water is heavy — about 1,700 pounds or 770 kg per cubic yard (0.76 cubic meters) — and it can move quickly in a torrent, sweeping people to their deaths, tossing boats and vehicles, and pulverizing buildings. Six inches of fast-moving water is enough to knock over an adult, says the National Hurricane Center (NHC). Flooding becomes even more dangerous when it coincides with high tide.

Hurricane Katrina in 2005 caused storm surges of over 25 feet along the Mississippi coast. According to the NHC, many of the 1,500 people killed died directly or indirectly as a result of the storm surges.

What impact will Hurricane Milton have?

According to the National Weather Service, storm surge is often the greatest threat to life and property from a hurricane. In the past, severe hurricanes have often resulted in high fatalities due to rising ocean levels.

The National Weather Service is expecting life-threatening storm surges along Florida's Gulf Coast this week, with storm surges as high as 8 to 12 feet above ground level predicted in some areas.

On Monday, officials in Sarasota County, Florida, issued evacuation orders, saying the forecast storm surge from Milton there was twice that of Hurricane Helene.

Experts in Sarasota are predicting a storm surge of 10 to 12 feet for the area, which they say is not survivable on the barrier islands.

According to the National Oceanic and Atmospheric Administration (NOAA), hurricane storm surges can cause significant damage and “severely erode beaches and coastal roads,” as well as destroy boats and buildings.

“As water moves inland, rivers and lakes may be affected, contributing to an increase in flooding,” the administration said.

In 2022, Hurricane Ian caused catastrophic storm surge on the southwest and northeast coasts of Florida. Storm surge was up to 18 feet in some areas.

What role does the climate crisis play?

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

Researchers have found that the number of storms escalating into Category 4 or 5 hurricanes with winds of at least 131 miles per hour (210 km/h) has roughly doubled in the North Atlantic since the 1970s. “Historically, if you look back, storms have strengthened more slowly than they do today,” said Phil Klotzbach, a researcher at Colorado State University who specializes in hurricane forecasting.

What will the long-term costs be?

The costs of extreme weather events related to the climate crisis continue to rise. There were a record 28 disasters in the U.S. last year, each costing at least $1 billion.

According to an estimate by private meteorologist AccuWeather following Hurricane Helene, damage could be between $225 billion and $250 billion.