NOAA has issued a release explaining this year’s quiet hurricane season. Note how they describe the conditions that prevented-life endangering hurricanes as “unfavorable”:
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 atNOAA’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.
The whole thing here.
And, FWIW, the 2013 hurricane season was such a dud that the NWS started maintenance repairs on the Doppler radar site that covers Miami before the season even ended.