Colorado State University meteorologists Philip Klotzbach and William Gray

This year's storms, which included five hurricanes, were the fewest in the Atlantic basin since seven formed in 1997. A record 28 storms formed last year, 15 of which became hurricanes. They included Hurricane Katrina, which devastated New Orleans and caused more than 1,800 deaths.

Colorado State University meteorologists Philip Klotzbach and William Gray in December, April and May predicted a season of 17 named storms and nine hurricanes, which would have been more- active than normal. In August, they cut the forecast because of climate disruptions caused by a late El Nino weather pattern in the Pacific and dryness in the tropical Atlantic.

"A variety of factors interact with each other to cause year-to-year and month-to-month hurricane variability," Klotzbach said in a statement. "It is impossible to understand how all these processes interact with each other to 100 percent certainty."

No hurricanes made landfall in the U.S. this year, the first time that has happened since 2001 and only the 11th time since 1945, Gray said in the statement. Three tropical storms made landfall this year.

The Atlantic hurricane season officially ends on November 30. The last named storm to form in the Atlantic basin was Hurricane Isaac, which became a tropical storm on September 28 and a hurricane on September 30.

Colorado State will release the first forecast for the 2007 Atlantic basin hurricane season December 8.