Wednesday, April 25, 2018
Tampa Bay Weather

2017 Hurricane Season: El Niño will decide how active this storm season will be

If forecasters get it right, the 2017 hurricane season will see fewer storms than normal. Those storms will be of lesser intensity. And there will be less chance they'll make landfall.

But if forecasters get it wrong, blame El Niño.

The Pacific weather phenomenon could once again determine how rough the Atlantic hurricane season gets. Will we see a repeat of a very active 2016 storm season, when two destructive storms lashed Florida? Or a return to the sedate decade that preceded last year?

"It's still quite uncertain," said Michael M. Bell, a Colorado State atmospheric sciences professor and coauthor of the university's annual storm forecast. "The ocean temperatures off the coast of South America are already warm, but we have a lot of difficulties predicting whether or not an El Niño will form when we're looking at it in the spring."

El Niño is what scientists call the weather phenomenon of warmer-than-average water temperatures in the eastern and central Pacific. The warmer water creates high-altitude winds that move across the tropical Atlantic Ocean, where most Atlantic hurricanes form, making it harder for storms to form and strengthen.

If El Niño performs as expected in the Pacific, it should tamp down on storm formations in the Atlantic.

Colorado State University's Tropical Meteorology Project has predicted that there will be 11 named storms this year, four hurricanes and two major storms — hurricanes that are Category 3 or higher. Under the Saffir-Simpson measure of wind strength, those are hurricanes with wind s in excess of 111 mph.

Eleven named storms is fewer than the median from the years 1981 to 2010, during which there were 12 named storms, 6.5 hurricanes and two major hurricanes.

The storm season doesn't officially start until June 1 and runs until Nov. 30, yet the Atlantic has already seen its first storm. In April, Tropical Storm Arlene formed east of Bermuda, lasted only three days and did not impact land.

Last year saw an out-of-season hurricane, too, when Hurricane Alex formed in January.

Is that because of climate change? Bell said it's too soon to tell if rising water temperatures are making oceans more conducive to hurricanes forming outside of the traditional June-to-November window. Historically, about 97 percent of cyclones occur during hurricane season, Bell said, meaning roughly one out of every 33 happen out of season.

Florida underwent an unprecedented 11-year hurricane drought, from 2005 to 2016, during which no hurricanes made landfall in the Sunshine State.

That ended in 2016. In September, Hurricane Hermine made landfall in Apalachee Bay as a Category 1 storm, causing an estimated $550 million in damage up and down the Gulf Coast and two deaths.

Weeks later, Hurricane Matthew churned through the Caribbean and zeroed in on the Florida coast as a powerful Category 5 storm, unleashing devastating winds of up to 165mph.

While it never officially made landfall in Florida, it spent several days in October damaging the east coast as a weaker storm. Total U.S. damage was estimated to be roughly $10 billion. There were 585 deaths directly linked to the storm, including 546 in Haiti alone and 34 in the United States, according to the National Hurricane Center.

This year's Colorado State report forecasts a lower-than-average probability of a storm making landfall this year. The chance of a hurricane coming ashore along the U.S. East Coast, including Florida, is 51 percent, according to the forecast. That coast has been struck at least once by a hurricane in 61 of the last 100 years.

The chances of a hurricane striking the Atlantic side of the U.S. coastline — from the Texas-Mexico border to Maine — is 75 percent. Historical data suggests the probability of landfall over the last century was 84 percent.

The reason the predicted landfall probabilities are lower this year, Bell said, is that there are fewer storms forecast.

Another reason for the reduced numbers is the cooler-than-normal water in the northern Atlantic. Like El Niño, Bell said, lower northern Atlantic temperatures contribute to wind sheer, which can also prevent storms from strengthening into hurricanes.

The mild winter, which resulted in warmer temperatures in the Gulf of Mexico, shouldn't have much impact, said Phil Klotzbach, a Colorado State research scientist and Bell's coauthor. The gulf is always warm, he said, so storms that enter it are likely to strengthen anyway. And, Klotzbach said, most storms don't form in the gulf.

Yet the below-average storm forecast doesn't mean much to local officials. They must prepare the same way every year, Pasco County Emergency Services director Kevin Guthrie said.

There's more to worry about during storm season than just hurricane-force winds. Much of Pasco has found itself under water over the last two summers: in 2015, during record rainfall in the Tampa Bay region and last year because of Hurricane Hermine.

"It doesn't matter how many storms you have in a season, it only takes one," Guthrie said. "We could have a hurricane season with only three named storms, but if just one of those storms comes into the Tampa Bay area, that's a bad day."

The 2015-16 rain events also contributed to sewage spills in Pinellas County and especially in St. Petersburg. The city's overburdened and outdated sewer system released about 200 million gallons of wastewater into neighborhoods and into Tampa Bay.

Guthrie said Florida residents cannot fall into the trap of thinking a below-average forecast means they don't need to prep for storm season.

He recalled 1992, an otherwise below-average season with the huge exception of Hurricane Andrew, a Category 5 storm that caused $24 billion in damage in 2015 dollars. It is the third-costliest catastrophe in U.S. history, according to Florida International University's International Hurricane Research Center. Hurricane Katrina in 2005 was No. 1, and the Sept. 11 terrorist attack was second.

Guthrie outlined three steps people should take to get ready for hurricane season:

First, do the research: Do you live in a flood zone, a storm surge zone or an evacuation zone?

Second, prepare a hurricane kit whether hunkering down for a storm or evacuating to a shelter. You should be prepared to take important paperwork, prescriptions and irreplaceable valuables like family photos with you. You and your family will also need enough food and water to last up to five days until help or more supplies arrive in your area.

Hopefully, the third step doesn't come to pass: Heed evacuation orders and seek shelter. But steps one and two will prepare you for that.

"When we say disasters are local, we don't mean local government," Guthrie said. "We mean the local citizen.

"So it starts with that individual having a plan.

Contact Josh Solomon at (813) 909-4613 or [email protected] Follow @josh_solomon15.

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