Atlantic Ocean "primed" to develop series of powerful hurricanes

By PBS Newshour, adapted by Newsela staff 09/11/2017

Two weeks ago, Hurricane Harvey tore through Texas and Louisiana, causing at least 60 deaths and billions of dollars in damages. Then, Hurricane Irma came along.

Last week Irma grew into a Category 5 storm — with wind speeds exceeding 156 miles per hour — as it moved toward the Caribbean and southern Florida. It downgraded on Friday to a powerful category 4, but if the storm maintains course and gains more ferocity, it will rewrite the history books. And there are more storms coming.

“The U.S. has never been hit, since we started collecting records in 1851, by two Category 4 or stronger hurricanes in the same season,” said Jeff Masters, a meteorologist, and co-founder of Weather Underground. Now, "that could happen.”

Here’s what to expect from the storm — plus an explainer on why this hurricane season is churning out so many extreme storms.

Will Cuba 'Save' Florida?

Friday, Hurricane Irma hit the Turks and Caicos islands and downgraded to a Category 4, but was still packing strong 150 mph winds. Computer models indicated it would move towards Cuba before hitting southern Florida. What happens there would largely determine what happens to the Florida Keys, Miami, and the rest of south Florida, Masters said.

“Cuba is a big island, with a lot of mountains. It could definitely destroy the inner core of Irma, if the storm were to spend more than 12 hours over Cuba,” he said. “That’s kind of Florida’s best hope right now.”

If the storm squeaks through these islands, then it’s likely to be a Category 4 or Category 5 hurricane when it hits, Masters had said.

But Irma did hit Cuba and was downgraded to a Category 2 on Sunday as it hit the Florida coast.

A Category 5 hurricane has not hit the mainland U.S. since Hurricane Andrew in 1992, and such an event has only happened to the nation three times since record-keeping began in 1851. Because of the rarity, Masters and other meteorologists are not calling for a Category 5 landfall in the U.S. at the moment.

Conditions Rife For Major Damage

Masters said, “The Atlantic is primed for making major hurricanes” right now due to three major ingredients.

First, and most important, is weak wind shear, says Philip Klotzbach, who studies the atmosphere at Colorado State University. Hurricanes lose power when winds near the ocean surface blow at one speed and direction while winds in the upper atmosphere blow another. This difference — or shear — causes a hurricane to physically tilt, like a spinning top, which dampens the force of the winds coming from it.

The other two ingredients are warm Atlantic ocean temperatures and high levels of moisture in the air. Irma is brewing in ideal sea temperatures of around 85 degrees Fahrenheit; such high ocean temperatures fuel intensification.

Irma followed on the heels of Harvey because of a change in air pressure along the East Coast, Klotzbach said.

“Over the last 10 to 12 years, we tend to have a ridge of low pressure along the East Coast, which has helped steer the storms away,” Klotzbach said. But this invisible ridge has pushed westward this year, leaving the eastern seaboard, the Caribbean, and the Gulf of Mexico exposed to hurricanes.

Dire Predictions Made In July

Some saw this coming. In early July, Klotzbach’s team at Tropical Meteorology Project predicted the Atlantic Ocean would experience an above-average hurricane season because of the El Niño-Southern Oscillation (ENSO) — or rather because of its absence this year.

El Niño creates extremely warm temperatures in the Pacific Ocean, which pushes strong winds into the Atlantic, creates high levels of wind shear, and stops hurricanes. When Pacific sea temperatures reverse and cool, it creates La Niña, which tends to drive hurricanes.

Here’s the strange thing. ENSO is neutral this year, so you might expect an average year of Atlantic storms.

But 2017 has behaved much like 2005. Back then, ENSO was neutral, but the U.S. still experienced many colossal storms, including Hurricanes Katrina, Rita, and Wilma.

Harvey and Irma appear to be replicating that legacy. Harvey dumped a record 24 trillion tons of water onto Texas and Louisiana. Meanwhile, when Irma’s wind speeds reached 180 miles per hour Tuesday, it became one of the strongest Atlantic storms in history.

Irma's Power Is A Rarity

“We’ve only had 16 other hurricanes on record that have been as strong as Irma is right now,” Klotzbach said. Its 3.5 days and counting as a major hurricane trail only Hurricane Luis in 1995, too.

Florida is afraid to see damages on par with Hurricane Donna of 1960, Masters said.

Residents of the Florida Keys experienced 13-foot storm surges before Donna slashed up the East Coast. It became the only storm to produce hurricane-force winds in Florida, the Mid-Atlantic states, and New England. If a hurricane of this magnitude hit Florida today, it could cause between $50 billion to $100 billion in damages.

Klotzbach urged people to pay attention to whether hurricane watches or warnings have been issued for their communities. He does not expect Irma to dump as much rain as Harvey, but even if a storm doesn’t track directly over Miami, its storm surge could have a huge impact on south Florida, he said. Heavy rains, storm surge, and flooding will likely hit Georgia and the Carolinas.

Listen To Safety Officials

“Follow the advice of the local emergency management. They’ll tell you whether you should evacuate or shelter in place,” Klotzbach said.

A fake news story garnered more than 2 million shares on Facebook last weekend. It asked if Hurricane Irma and its 180-mile-per-hour winds could be considered a Category 6 storm?

No, said Masters.

There will never be a Category 6 storm, Masters says, "because Category 5 is already catastrophic." But climate change is expected to intensify the winds and rains of major storms over the next century.

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