Why Hurricane Irma's Winds Are An Extreme Worry For Florida

Sep 8, 2017
Originally published on September 8, 2017 11:25 am

Hurricane Irma, which battered the Caribbean with winds up to 185 mph, has its sights on Florida with winds now around 150 mph. according to the National Hurricane Center.

Those are really strong winds. Imagine speeding down the highway at 70 miles an hour with your car window open. You stick your hand out and hold it in the wind.

"Do you have a sense of how the wind is going to push your hand back?" asks David Prevatt, a professor of civil engineering at the University of Florida.

Now imagine getting out of his old Mazda and getting into a Maserati going 185 mph.

"The force that I will feel on my hand in comparison to that 70 miles per hour is going to be almost seven times as strong."

This is Prevatt's way of saying Hurricane Irma's top winds are exponentially stronger than anything most people have ever experienced.

And, he says, you also have to consider the uplift or suction force of winds.

"The wind is going to try to pull the roof and roof components vertically up and away from the ground," he says.

How well structures hold up depends not just on the strength of building materials, but more importantly, the strength of the connections holding roofs, walls and foundations together.

What about high-rises? They may have a better chance of staying upright — until something flies into them, explains Northwestern University civil engineering professor Joseph Schofer.

"Tall structures are not particularly vulnerable except for damage from flying objects," he says, "and fairly large objects will be boosted into the air with wind speeds like this."

Wind isn't the only concern, Schofer says. So is flooding from rain and the storm surge, which he calls "a particularly threatening problem along the coast."

Schofer says a high storm surge could be stronger than wind and knock down buildings, bridges and other seaside structures.

And because sea levels are higher, any storm surge that comes ashore with Irma will be that much more damaging, adds Carol Considine, professor of engineering technology at Old Dominion University.

"We are definitely going to have roadways that may be undermined and damaged because from this type of storm," she says. "You're also going to have coastal flooding, which could inundate the stormwater systems in communities."

Dams and levees are vulnerable to a storm of Irma's strength, too, as is the electric power grid.

Many of these systems are more resilient today than they were in the past — building codes have improved since Hurricane Andrew 25 years ago. But, Considine says, we shouldn't just improve standards based on past storms.

"We need to start to think about what do we expect in the future and start changing the way we design to anticipate some of those future events," she says.

Afterall, she says, storms are getting worse, and Hurricane Irma is a prime example.

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DAVID GREENE, HOST:

Hurricane Irma is now a Category 4 hurricane. That is down from a 5. Still, maximum sustained winds of 155 miles an hour. This is slightly weaker from when Irma wiped most of the structures off of islands it passed over in the Caribbean. Now, as the storm heads towards the United States mainland, Florida Governor Rick Scott warned people in evacuation zones not to ride this out.

(SOUNDBITE OF ARCHIVED RECORDING)

RICK SCOTT: Based on what we now know, Miami-Dade will have major hurricane impacts with deadly storm surge - deadly storm surge - and life-threatening winds. We can expect this all along the entire East Coast.

GREENE: Well, Nancy Masry (ph) from Key West heeded this call. She was on the Florida Turnpike when we reached her. She said she was pressured by friends and family to evacuate.

NANCY MASRY: I just got back, about a week ago, from a two-week road trip and the last thing I really wanted to do was get back in a car and live out of a suitcase.

GREENE: And here's NPR's David Schaper on how bad this storm could be.

DAVID SCHAPER, BYLINE: Imagine speeding down the highway at 70 miles an hour with your car window open.

DAVID PREVATT: And you stick your hand out and you hold it in the wind. Do you have a sense of how the wind is going to push your hand back?

SCHAPER: David Prevatt, a professor of civil engineering at the University of Florida, says, now imagine getting out of his old Mazda and getting into a Maserati going 185.

PREVATT: The force that I will feel on my hand, in comparison to that 70 mile per hour, is going to be almost seven times as strong.

SCHAPER: This is Prevatt's way of saying Hurricane Irma's top winds are exponentially stronger than anything most people have ever experienced before. Prevatt says another element to consider is the uplift, or suction force, of the winds.

PREVATT: The wind is going to try to pull the roof and roof components vertically up and away from the ground.

SCHAPER: So how well structures hold up depends, not just on the strength of building materials, but, more importantly, the strength of the connections holding roofs, walls and foundations together. What about high rises? Northwestern University civil engineering professor Joseph Schofer answers that concern.

JOSEPH SCHOFER: Tall structures are not particularly vulnerable, except for damage from flying objects. And clearly, large objects are going to boosted into the air with a wind speed like this.

SCHAPER: And Schofer says wind isn't the only concern - so, too, is water.

SCHOFER: Flooding is going to be a problem because of the rain, but the storm surge is going to create a particularly threatening problem along the coast.

SCHAPER: Schofer says a high storm surge could be stronger than wind and knock down buildings, bridges and other seaside structures. And Carol Considine, a professor of engineering technology at Old Dominion University, adds that because sea levels are higher, any storm surge that comes ashore with Irma will be that much more damaging.

CAROL CONSIDINE: We're definitely going to have roadways that may be undermined and damaged from this type of storm. You're also going to have coastal flooding which could inundate the stormwater system in communities.

SCHAPER: Dams and levees are vulnerable to a storm of Irma's strength too, as is the electric power grid. Many of these systems are more resilient now. Building codes have improved since Hurricane Andrew 25 years ago. But, Considine says, we shouldn't just improve standards based on past storms.

CONSIDINE: We need to start thinking about, what do we expect in the future and start changing the way we design to anticipate some of those future events?

SCHAPER: After all, she says, storms are getting worse, and Hurricane Irma is a prime example.

GREENE: David Schaper. Transcript provided by NPR, Copyright NPR.