Confidence that 2018 will experience a below normal hurricane season increased substantially this week as global forces align to temper tropical activity.
An updated forecast released Thursday by the federal Climate Prediction Center is now calling for a 60 percent chance of a less active storm season, a hefty jump from a May forecast that predicted only a 25 percent probability of below normal activity.
Gerry Bell, the center’s lead seasonal hurricane forecaster, said the growing likelihood that a storm-thwarting El Nino will form in the fall combined with tropical Atlantic water temperatures that are the coldest since the 1990s were key factors in making the new prediction.
The forecast comes as Florida enters the peak of hurricane season between mid-August through October when 95 percent of hurricanes form. Already four named storms – Alberto, Beryl, Chris and Debby – have spun up this season. Beryl and Chris both mustered hurricane strength.
As of Thursday afternoon, Tropical Storm Debby was still churning harmlessly in the northern Atlantic.
And hurricane experts warned Thursday there will be more storms.
“It’s not dead,” said Stanley Goldenberg, a meteorologist with the Hurricane Research Division of the National Oceanic and Atmospheric Administration. “Storms can pop up quickly and we do expect more storms.”
An average hurricane season has 12 named storms, six hurricanes and two major hurricanes.
The hyperactive 2017 storm season produced 17 named storms, 10 hurricanes and six major hurricanes.
Bell said when the May forecast was released the chances an El Nino would form were only 45 percent.
An update this week puts the odds of an El Nino forming in the fall at 65 percent and up to 70 percent of a winter El Nino that could last into 2019. Bell compared this season to 2015, which had 11 named storms and 4 hurricanes.
“Please remember the hurricane seasonal outlooks are a general guide and do not predict landfalling storms,” Bell said. “Whether or not a storm strikes land is determined by the weather patterns in place when the storm approaches and those are generally not predictable until five to seven days in advance.”
Earth was put on an El Niño watch in June, but it’s not officially declared present until ocean temperatures in the equatorial Pacific are more than 1 degree above normal and are expected to maintain that temperature for six months.
After that, it can take 30 to 60 days for the atmosphere to respond.
The onset of El Niño occurs in tandem with the relaxation of the trade winds — those Earth-skimming easterlies that have guided sailing ships across the world’s oceans for centuries.
With the trade winds reduced, warm water that has piled up in the western Pacific Ocean and around Indonesia rushes back toward the east. That movement of warm water shifts rainfall patterns and the formation of deep tropical thunderstorms. The exploding storms whose cloud tops can touch the jet stream disrupt upper air patterns so winds come more out of the west.
The west winds create shear in the Atlantic, which can be deadly to budding hurricanes.
“The main message should be that no matter what this or any other prediction says that people must treat this like the peak of hurricane season and be prepared,” Goldenberg said. “Remember, 1992 was overall a very slow year.”
Category 5 Hurricane Andrew – the first named storm of the 1992 season – devastated areas of South Florida when made landfall Aug. 24.
At least 20 research groups, private companies and universities churn out annual hurricane forecasts, including the University of Arizona, The Weather Co. and Pennsylvania State University’s Earth System Science Center.