We've all seen the intrepid TV weatherman, hanging on to a wind-whipped lamppost for dear life — and, perhaps, for dear ratings — during a hurricane. But as we've probably all heard, it's not the wind that'll get you when a high-category storm heads your way: It's the water.
As residents of Florida and the Gulf Coast brace for Hurricane Michael, they'll hear lots about storm surge, a bulge of seawater that accompanies hurricanes. It is, statistically, the biggest culprit when it comes to death and destruction in a hurricane. Though to give credit where credit is due, storm surge is largely the result of high winds pushing the water along.
Either way, wind or water, the point remains: With hurricanes, it's best not to mess around.
What Is Storm Surge?
Crashing surf and rising rivers are signs of storm surge, which the National Oceanic and Atmospheric Association defines as the "abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide."
"Typically, there are two factors," says Steve Weagle, the chief meteorologist for WPTV in West Palm Beach, Florida, explaining what causes storm surges. "One is lower atmospheric pressure, the other is wind blowing across a water body, the friction piling the water up against the coastline."
Lots of other factors come into play to determine the size of the surge, such how big and how strong the storm is, and something that meteorologists call "fetch," or how far winds travel across the water. Combine those with things like the height of the tide, the slope of the sea floor as it approaches the shore, how the storm hits the coast (a glancing blow, straight on), where the prevailing winds are as it lands in a particular area ... all can create a surge that can push water levels 20 feet (6 meters) higher than normal or more, according to the National Hurricane Center. In 2005, Hurricane Katrina pushed a surge more than 30 feet (9 meters) high in parts of Louisiana. The world record, set in Australia in 1899, is believed to be over 42 feet (12 meters).
These are not tsunamis, in which a killer wave comes out of nowhere. (Tsunamis are caused by physical disturbances, like earthquakes or volcanic eruptions.)
"Usually, it's a gradual increase. Over hours and hours as the storm approaches, the water slowly gets higher and higher," Weagle says. "And that's what catches people off guard. Typically, the peak for the storm surge is right at landfall or shortly after."
How Dangerous Are We Talking?
It is the water, not the wind, that causes the most damage in hurricanes. And don't think just because you might live a little inland that storm surge can't get to you. Water pushed by wind can flow up rivers and streams, too, and cause them and other bodies of water to overflow in often catastrophic flooding.
"We saw that during Florence and we'll see it again during Michael, where people who live 10, 15, 20 miles [16, 24, 32 kilometers] away from the coastline think they're not susceptible to storm surge. If they live along a tidal river, they are susceptible," Weagle says. "That water level will increase as the surge flows up the river." Even people around Lake Okeechobee, west of Palm Beach, Florida, in the middle of the state, will evacuate when a big storm is due, he says.
A report earlier this year estimated that 2018 hurricane storm surge could endanger 6.9 million homes and cost a potential $1.6 trillion in reconstructions costs. Storm surge costs, of course, can be even worse, as history has shown.
Hurricane Katrina killed more than 1,800 people in 2005. Some 40 percent died by drowning, according to a 2008 study, associated with a storm surge that breached 53 levees and swamped some 80 percent of the city and its surroundings.
"With Katrina, a lot of people, I think, were caught off guard with how high that surge got, given the fact that, 'Oh, since the storm weakened to a [Category] 3, the surge is not going to be as high,'" says Derek Beasley, the chief meteorologist at WFTX TV in Cape Coral, Florida. "The problem was, before that it was a 4 and a 5. So even though it dropped down to a 3, that momentum was still there. And it was a huge storm. So you have a big storm with a big wind like that, even if it weakens, it can lead to a big surge."
How to Avoid the Worst
One problem that coast-dwellers run into, Beasley says, is that they think they know hurricanes too well sometimes. Especially if they've been through a few of them.
"People feel like they can compare storms. There's this false sense of security, that, 'Oh I went through this storm, this one isn't as bad, so I think I'll be fine,'" says Beasley, who saw Katrina's effects when he worked at a station in Mississippi. "It's a perilous way of thinking. You can't compare storms."
The key to weathering surge is simple, Weagle says. Pay attention. And be prepared.
"Well, there's an old saying; run from water, hide from wind. So if you live along the coast, get away from the coast. And if you're inland, get in a well-protected home," he says. "People just need to get a plan. Most people don't have any idea if they're in an evacuation area and they have to leave. They don't do any planning. And that causes a lot of unnecessary stress."