Hurricane season of 2018 ends: How accurate were forecasters?
PALM BEACH, Fla.—The 2018 hurricane season began like a lazy river, a handful of circles spinning in an atmosphere still sleepy from spring.
Only Subtropical Storm Alberto made contact with the U.S., splashing into Laguna Beach, Fla., at the end of May before the calendar even noted the official June 1 start date of storm season. Through August, it was called the “season of slop,” seemingly confirming forecasts for below average cyclonic activity.
But then September came, the Atlantic basin caught fire, and two coasts would face the terrifying power of wind and water.
By the last day of the 2018 hurricane season on Friday, the cyclone scoreboard included 15 named storms, including eight hurricanes and two major hurricanes of Category 3 or higher. A normal season typically has 12 named storms, including six hurricanes and two major hurricanes.
“It’s not that things didn’t develop the way we thought they would,” said Colorado State University hurricane researcher Phil Klotzbach, whose August forecast called for 12 named storms. “Things played out exactly like we thought they would, and the storms came anyway.”
Both Klotzbach and the federal Climate Prediction Center had predicted higher activity in their early-season forecasts, but reduced the numbers as the chances of a storm-quelling El Nino increased.
At the same time, a persistent northeasterly trade wind blowing over the Atlantic led to cooler water and drier air— conditions less conducive for tropical formation.
But El Nino was a no-show, the winds quieted, and nature turned to the periphery of the tropics, cooking up storms farther north in the Atlantic basin where water temperatures were record warm.
On Sept. 10, there were three hurricanes churning simultaneously—Florence, Helene and Isaac. That’s only the 11th time on record that the Atlantic has had three hurricanes at the same time, according to Klotzbach.
“It was a bit of a surprise that the season was as active as it was,” said Gerry Bell, lead seasonal hurricane forecaster for the National Oceanic and Atmospheric Administration’s Climate Prediction Center. “Conditions were warming as we went through August.”
Florence’s growth shocked forecasters
Another key ingredient not forecast well by the models was the potent West African monsoon season, Bell said. Storms that form during the continent’s monsoon season from the southwesterly winds off the Atlantic mixing with a turbulent area north of the equator known as the Inter-Tropical Convergence Zone form the seeds for the tropical waves that can grow into fearsome Cape Verde hurricanes.
That’s where National Hurricane Center forecasters first saw an area of storminess that would become Florence.
Hurricane Florence spent 16 days in the Atlantic from its formation 425 miles east-southeast of the Cabo Verde Islands Aug. 30 to a Sept. 14 landfall in North Carolina as a Category 1 storm. It was the first major hurricane of the season, strengthening to a Category 4 Sept. 6 in an intensification NHC forecasters called “remarkable.”