(Phys.org) —The 2013 Atlantic hurricane season, which officially ends on Saturday, Nov. 30, had the fewest number of hurricanes since 1982, thanks in large part to persistent, unfavorable atmospheric conditions over the Gulf of Mexico, Caribbean Sea, and tropical Atlantic Ocean. This year is expected to rank as the sixth-least-active Atlantic hurricane season since 1950, in terms of the collective strength and duration of named storms and hurricanes.
"A combination of conditions acted to offset several climate patterns that historically have produced active hurricane seasons," said Gerry Bell, Ph.D., lead seasonal hurricane forecaster at NOAA's Climate Prediction Center, a division of the National Weather Service. "As a result, we did not see the large numbers of hurricanes that typically accompany these climate patterns."
Thirteen named storms formed in the Atlantic basin this year. Two, Ingrid and Humberto, became hurricanes, but neither became major hurricanes. Although the number of named storms was above the average of 12, the numbers of hurricanes and major hurricanes were well below their averages of six and three, respectively. Major hurricanes are categories 3 and above.
Tropical storm Andrea, the first of the season, was the only named storm to make landfall in the United States this year. Andrea brought tornadoes, heavy rain, and minor flooding to portions of Florida, eastern Georgia and eastern South Carolina, causing one fatality.
The 2013 hurricane season was only the third below-normal season in the last 19 years, since 1995, when the current high-activity era for Atlantic hurricanes began.
"This unexpectedly low activity is linked to an unpredictable atmospheric pattern that prevented the growth of storms by producing exceptionally dry, sinking air and strong vertical wind shear in much of the main hurricane formation region, which spans the tropical Atlantic Ocean and Caribbean Sea," said Bell. "Also detrimental to some tropical cyclones this year were several strong outbreaks of dry and stable air that originated over Africa."
Unlike the U.S., which was largely spared this year, Mexico was battered by eight storms, including three from the Atlantic basin and five from the eastern North Pacific. Of these eight landfalling systems, five struck as tropical storms and three as hurricanes.
Explore further: US Atlantic braces for active hurricane season (Update)