The Atlantic Hurricane season, which officials ends Nov. 30, will go into the record books as the quietest since 1997, due to the impact of the El Nino weather phenomenon, forecasters at Colorado State University said Thursday.

The season featured nine named storms, three hurricanes and two major hurricanes, with sustained winds of 111 miles per hour or greater. Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes per season.

In their far-forward December 2008 forecast, experts at Colorado State projected an above-average season, with 14 named storms and seven hurricanes. The forecasters said the impacts of El Nino, unforeseen at the time, sharply reduced hurricane formation, and they reduced their storm expectations as the season progressed.

"Activity in 2009 was reduced considerably due largely to the moderate El Nino event that developed," said William Gray, who has been issuing forecasts for 26 years. "This event generated significantly stronger-than-average vertical wind shear, especially in the Caribbean and Gulf of Mexico."

The forecasters said five named storms dissipated over the open ocean this year, a fairly rare occurrence, caused by unusually high levels of vertical wind shear, caused by El Nino.

El Nino is the name given to the unusual warming of the waters of the equatorial Pacific Ocean, which have widespread impact. The National Oceanic and Atmospheric Administration said Thursday moderate El Nino conditions are expected to persist through the winter. While a strong event is possible, NOAA said it isn't considered likely. El Nino is a factor in expected above-normal temperatures forecast for the Western U.S. through February, NOAA said.

Hurricane season had only a modest impact on oil and natural gas production in the U.S. Gulf of Mexico. Rigs were evacuated and production curtailed briefly as Hurricane Ida passed through the region earlier this month. At its peak some 560,000 barrels a day of crude output, equal to about 10% of total U.S. daily flow, was shut-in, but that quickly dropped to less 30,000 barrels a day by the end of last week, according to federal Minerals Management Service.

Only two, weak tropical storms made landfall in the season, compared with a long-term average of 3.6.

The season, which begins in June, was late in starting, and didn't record its first storm until Aug. 15, the latest such occurrence since 1992. The season's nine named storms and three hurricanes and two major hurricanes all were the fewest recorded since 1997.

No Category 5 storms, with sustained winds of 155 mph or more, were recorded, for the second-straight year. The latest time two or more consecutive seasons didn't have a Category 5 storm was in 1999-2002, the forecasters said.

Despite the relative quiet of 2009, the Atlantic region is experiencing a multi-decadal natural cycle of stronger storm activity, the forecasters said. This isn't directly related to global sea surface temperature increases or atmospheric concentrations of carbon dioxide, Gray said.

With the 2009 season's official end at hand, forecasters are preparing their first outlook for the 2010 season, to be released Dec. 9.

In the past 11 years, Colorado State said, its December forecasts have correctly predicted above-normal, or below-normal activity 62% of the time, with the accuracy rate of the updated June report at the season's start, rising to above 80%.