If this year’s hurricane season has seemed quiet so far, it will likely continue to do so. In an update to the Atlantic Hurricane Season Outlook, the National Oceanic and Atmospheric Administration predicts there is a now a 70 percent chance of a below-normal season. There is only a five percent chance of an above-normal season.
The updated hurricane season outlook, which includes the activity to-date of hurricanes Arthur and Bertha, predicts a 70 percent chance of the following ranges: 7 to 12 named storms (top winds of 39 mph or higher), including 3 to 6 hurricanes (top winds of 74 mph or higher), of which 0 to 2 could become major hurricanes (Category 3, 4, 5; winds of at least 111 mph).
These ranges are centered below the 30-year seasonal averages of 12 named storms, six hurricanes and three major hurricanes. The initial outlook in May predicted 8 to 13 named storms, 3 to 6 hurricanes and 1 to 2 major hurricanes.
According to Gerry Bell, lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center, the environment over the North Atlantic remains hostile for tropical cyclone development. “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,” he said in a NOAA press release.
A big reason for those unfavorable conditions, of course, is the El Nino event that has been brewing in the equatorial Pacific since the beginning of 2014. Sea surface temperatures in the region are warmer than average, but all of the factors that lead to an El Nino being declared haven’t quite fallen into place. In its update on Thursday, the Climate Prediction Center was giving El Nino a 65 percent chance of developing this year, which is down from earlier forecasts.
El Nino suppresses tropical cyclone development by increasing wind shear over the North Atlantic. High wind shear, which is the change in wind speed with height, tends to tear hurricanes apart, often before they’ve even had a chance to develop.
In addition to the hostile winds, sea surface temperature has also been running cooler than average in the tropical Atlantic. Models predict that these cool waters will likely persist throughout the hurricane season.
Three tropical cyclones have formed in the Atlantic so far in 2014. Hurricane Arthur made landfall in North Carolina in early July as a category 2. Tropical Depression Two, the season’s weakest storm so far, never made it to the Lesser Antilles. Hurricane Bertha, which (surprisingly) lasted as a tropical cyclone until Wednesday, maxed out at a category 1.