2013: the Hurricane Season that wasn’t

The National Oceanic and Atmospheric Administration released its 2013 forecast on May 23, which called for an active or extremely active hurricane season, predicting that there was a 70 percent chance of having 13 to 20 named storms, of which seven to 11 could become hurricanes, including three to six major hurricanes (categories 3-5).

However, when the 2013 season concluded on November 30, it had not produced a single land-falling hurricane in the U.S. Instead of having above-average storm activity, as the seasonal hurricane outlooks unanimously called for, the season had been quiet — notable for its inactivity.

Overall, 13 systems spun up in the basin since June 1, one more than average for the season, Accuweather reported.

Hurricanes, however, were in short supply. Only two, Ingrid and Humberto, formed during the 2013 season, compared to the average of six. Of those two, neither became major hurricanes. A major hurricane is defined as a storm that reaches Category 3 or higher. Typically, the Atlantic yields three major hurricanes per season.

While pre-season outlooks rarely, if ever, have pinpoint accuracy, they don’t usually miss by such a large margin, noted Climate Central. Forecasters say that three main features loom large for the inactivity: large areas of sinking air, frequent plumes of dry, dusty air coming off the Sahara Desert, and above-average wind shear. None of those features were part of their initial calculations in making seasonal projections. Researchers are now looking into whether they can be predicted in advance like other variables, such as El Niño and La Niña events.

Brian McNoldy, a senior research associate at the University of Miami, said that across the Atlantic this season “you had air sinking through a pretty large depth of the atmosphere.” Sinking air inhibits storm formation by causing air to become drier and more stable, thereby stunting the growth of thunderstorms that require moist, unstable air in order to thrive.