Updated outlook calls for 90 percent probability of below-normal season
August 6, 2015
(Credit: NOAA)
The NOAA Climate Prediction Center’s updated 2015 Atlantic Hurricane Season Outlook calls for a 90 percent chance of a below-normal hurricane season. A below-normal season is now even more likely than predicted in May, when the likelihood of a below-normal season was 70 percent.
“Tropical storms and hurricanes can and do strike the United States, even in below-normal seasons and during El Niño events,” said Gerry Bell, Ph.D., lead seasonal hurricane forecaster with NOAA’s 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.”
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 90 percent probability of a below-normal season is the highest confidence level given by NOAA since seasonal hurricane outlooks began in 1998.
“Tropical storms and hurricanes can and do strike the United States, even in below-normal seasons and during El Niño events,” said Gerry Bell, Ph.D., lead seasonal hurricane forecaster with NOAA’s 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.”
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 90 percent probability of a below-normal season is the highest confidence level given by NOAA since seasonal hurricane outlooks began in 1998.
Satellite image of Subtropical Storm Ana forming off the East Coast. This image was taken by GOES East on May 8, 2015. (Credit: NOAA)
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 (from 6-11 in the initial May Outlook), of
which 1-4 will become hurricanes (from 3-6 in May), and 0-1 will become
major hurricanes (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 high likelihood of a below-normal season to three primary factors:
Forecasters attribute the high likelihood of a below-normal season to three primary factors:
- El Niño has strengthened as predicted, and NOAA’s latest El Niño forecast calls for a significant El Niño to continue through the remainder of the hurricane season;
- Atmospheric conditions typically associated with a
significant El Niño, such as strong vertical wind shear and enhanced
sinking motion across the tropical Atlantic and Caribbean Sea, are now
present. These conditions make it difficult for storms to develop, and
they 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.
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