Mild U.S. Hurricane Season Defied Predictions

November 30, 2006

The hurricanes that some feared would pummel the U.S. in 2006 never materialized because of a combination of unusual weather conditions, scientists say.

Forecasters at Colorado State University and the U.S. National Oceanic and Atmospheric Administration (NOAA) predicted in June that as many as 17 tropical storms and 5 major hurricanes with winds of at least 111 miles (178 kilometers) an hour would form in the Atlantic Basin.

Edgy residents living along the Atlantic Coast braced for a rowdy summer similar to those of the past two years, during which 13 major hurricanes formed.

But with the end of the official 2006 hurricane season today, only nine tropical storms have formed, the last one in early October.

Only two of the storms—Gordon and Helene—evolved into major hurricanes, meaning they had peak winds of 120 miles (193 kilometers) an hour or more, but both stayed well offshore from the U.S. mainland.

El Niño's Effects

Phil Klotzbach, a hurricane researcher at Colorado State University in Fort Collins, said an occasional weather phenomenon known as El Niño formed unusually late in the summer and put a damper on the storm season.

In addition, researchers at the University of Wisconsin reported evidence that dust blowing off West Africa—where many hurricanes begin as thunderstorms rolling off the coast—also may have inhibited storm formation in the Atlantic. (Related: "Hurricane Secrets May Be Revealed by African Thunderstorms" [August 3, 2006].)

(See an interactive feature on how hurricanes form.)

El Niño is an extensive warming of waters in the tropical Pacific Ocean near the Equator. When this phenomenon occurs, it can have dramatic consequences around the world, causing droughts in some places and flooding elsewhere.

Lian Xie, a meteorologist at North Carolina State University in Raleigh, said El Niño can also create upper-level winds known as wind shear over the Atlantic, which can suppress hurricane formation. In 1997, the last time an El Niño event occurred, only eight Atlantic tropical storms formed.

What made this year's El Niño unusual, however, was that it formed in September, which is usually the peak month for hurricane formation.

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