The NOAA Climate Prediction Center updated its 2015 Atlantic Hurricane Season Outlook today and now calls for a 90 percent chance of a below-normal hurricane season, the highest confidence level given by NOAA since hurricane outlooks began in 1998. When the outlook was first released in May, there was a 70 percent chance of a below-normal season.
“Tropical storms and hurricanes can and do strike the United States, even in below-normal seasons and during El Niño events,” said Gerry Bell, lead seasonal hurricane forecaster with the Climate Prediction Center. “Regardless of our call for below-normal storm activity, people along the Atlantic and Gulf coasts should remain prepared and vigilant, especially now that the peak months of the hurricane season have started.”
The updated outlook also lowers the overall expected storm activity this season. The outlook now includes a 70 percent chance of 6-10 named storms (down from 6-11 announced in May), of which 1-4 will become hurricanes (down from 3-6 in May), and 0-1 will become major hurricanes (down from 0-2 in May). These ranges — which include the three named storms to date (Ana, Bill, and Claudette) — are centered well below the seasonal averages of 12 named storms, 6 hurricanes and three major hurricanes.
Forecasters attribute the likelihood of a below-normal season to three factors: El Niño has strengthened and is forecast to continue through the hurricane season; atmospheric conditions associated with a significant El Niño, such as strong vertical wind shear and enhanced sinking motion across the tropical Atlantic and Caribbean Sea, are predicted to continue through the remaining four months of the hurricane season; and tropical Atlantic sea-surface temperatures are predicted to remain below average and much cooler than the rest of the global tropics.
Two tropical storms already have struck the United States this year. Ana made landfall in South Carolina in May, and Bill made landfall in Texas in June. The Atlantic hurricane season runs from June 1 through Nov. 30.