There is a higher likelihood of a below-normal hurricane season, according to an update to the Atlantic Hurricane Season Outlook issued by the National Oceanic and Atmospheric Administration.
The prognostication calls for a 70 percent chance of a below-normal season, a 25 percent chance of a near-normal season, and only a five percent chance of an above-normal season for the season, which runs through November 30.
“We are more confident that a below-normal season will occur because atmospheric and oceanic conditions that suppress cyclone formation have developed and will persist through the season,” said Gerry Bell, Ph.D., lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center, a division of the National Weather Service.
The update, which accounts for hurricanes Arthur and Bertha, predicts seven to 12 named storms (top winds of 39 miles per hour or higher), including three to six hurricanes (top winds of 74 miles per hour or higher). Of the hurricanes, zero to two could become major (Category 3, 4, or 5, with winds of at least 111 miles per hour).
The specific factors influencing the change to the forecast include:
Overall atmospheric conditions are not favorable for storm development. This includes strong vertical wind shear, a weaker West African monsoon, and the combination of increased atmospheric stability and sinking motion. These conditions mean fewer tropical systems are spawned off the African coast, and those that do form are less likely to become hurricanes. These conditions are stronger than originally predicted in May and are expected to last mid-August through October, the peak months of the hurricane season;
Overall oceanic conditions are not favorable for storm development. This includes below-average temperatures across the Tropical Atlantic, which are exceptionally cool relative to the remainder of the global Tropics. This cooling is even stronger than models predicted in May and is expected to persist through the hurricane season; and
El Niño is still likely to develop and to suppress storm development by increasing vertical wind shear, stability and sinking motion in the atmosphere.
But forecasters caution that the outlook does not predict how many storms will strike land.
“Nonetheless, tropical storms and hurricanes can strike the U.S. during below-normal seasons, as we have already seen this year when Arthur made landfall in North Carolina as a category-2 hurricane. We urge everyone to remain prepared and be on alert throughout the season,” Bell said.