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Hurricane forecasters predict a strong El Niño weather pattern this year will likely lead to another quiet Atlantic hurricane season, but there's a caveat: Similar conditions prevailed in 1992, which was the last time a Category 5 storm struck the United States.
Still, if early predictions for a quiet storm season prove true, it would be the third straight year of limited hurricane activity and insured losses.
In light of that prospect, a researcher at Colorado State University's respected Tropical Meteorology Project is investigating whether a third consecutive below-average season indicates that the U.S.-Atlantic Basin is entering a period where atmospheric conditions will be less likely to lead to hurricane formations.
Tropical Storm Ana, which affected the Carolinas in May, began the season before its official June 1 start. But experts say this has zero predictive value for the rest of the Atlantic hurricane season, which ends Nov. 30 and in which an average of 12 named storms form.
CSU researchers project there will be seven named storms this year, citing a moderate to strong El Niño weather pattern that limits hurricane formations in the Atlantic Ocean. The projection includes three storms becoming hurricanes and one becoming a major hurricane with winds of 111 mph or more.
There is a 28% probability that the U.S coastline north of Florida will see a landfall, probabilities that decline to 15% for the East Coast including the Florida peninsula and the Gulf Coast from the Florida panhandle to Brownsville, Texas, the forecast predicts.
It's possible the projection for total named storms may be revised to eight, including Ana, said Phil Klotzbach, a CSU researcher and lead author of the Tropical Meteorology Project forecast.
A forecast from Coastal Carolina University in Conway, South Carolina, sees seven to 10 named storms with three to six of those hurricanes, said Len Pietrafesa a Burroughs & Chapin Scholar at the university. The U.S. National Oceanic and Atmospheric Administration is to make its inaugural 2015 hurricane forecast this week.
In a May briefing after Tropical Storm Ana, James Franklin, chief of the hurricane specialist unit of NOAA's Miami-based National Hurricane Center, said though it is unusual for a named storm to form in May, it does happen every six or seven years and has occurred 23 times since 1851.
“There's always as tendency to want to draw conclusions from what happens early in the season,” Mr. Franklin said. “It's usually pretty hard to do that.”
Mr. Klotzbach agreed. “It doesn't really relate at all to what the rest of the season will bring,” said the researcher who is working on a paper about whether a third straight below-normal year would indicate that the U.S. is entering a longer period of less favorable hurricane conditions. “I would say at this point it is an unanswered question,” Mr. Klotzbach said.
Several experts said quiet and active hurricane periods become clear only in retrospect.
Because Ana formed outside the tropics, “it doesn't really tell us what's going to happen in the tropics at all,” said Tim Doggett, assistant vice president and senior principal scientist at catastrophe modeling firm AIR Worldwide Corp., referring to where the stronger storms form.
The return of El Niño is a factor in this year's forecasts, said NOAA's Mr. Franklin. “We are in an El Niño, and El Niño seasons typically have below-normal amounts of activity in the Atlantic,” he said.
In a mid-May report, NOAA's Climate Prediction Center and the International Research Institute for Climate and Society said there's a roughly 90% chance that El Niño will continue through the summer and a more than 80% chance that it will last through the year for the Northern Hemisphere.
Aside from producing warmer water in parts of the Pacific Ocean, El Niño also increases wind shear, which inhibits formation of hurricanes in the Atlantic, Mr. Pietrafesa said.
“It does certainly look like El Niño conditions are setting up for the Pacific, so that particular climate scenario is indicating that we're probably looking at below-average activity for the season,” said Mr. Doggett.
“The Atlantic is a lot cooler than it has been for the past five to 10 years,” Mr. Klotzbach said. That also keeps storms from forming. “Even in an El Niño year, there still can be periods of time when devastating storms can form,” Mr. Franklin said, pointing to Hurricane Andrew.
Andrew, which devastated Southern Florida and is one of only three Category 5 hurricanes to hit the U.S coast since 1900, came during an inactive hurricane season, said Karen Clark, co-founder and president of catastrophe modeling firm Karen Clark & Co. in Boston.
Andrew, the third-costliest U.S. hurricane and fourth-costliest natural disaster since 1950 according to Aon Benfield's Impact Forecasting (see chart, page 1), was the first named storm of 1992, but did not form until late August.
“This shows you that a Category 5 storm can happen at anytime,” Ms. Clark said.
Insured losses are driven by storm intensity and landfall location rather than storm frequency, she said. When considering expected average annual hurricane losses of $12 billion to $15 billion since 1900, “80% of those losses come from the top 20% of loss producing storms,” Ms. Clark said.