A total of 14 named storms, including six hurricanes developed in 2007, making it an average season.

Forecasters had initially expected at least 17 named storms, nine of them hurricanes to form during the six-month Atlantic season that officially ends on November 30.

"The reasons for this year's average season are challenging to explain," said Phil Klotzbach of the prominent Colorado State University hurricane forecast team.

"It is impossible to understand how all these processes interact with each other to 100-percent certainty," Klotzbach said in a report published on Tuesday, which looked at vertical wind sheer, sea surface temperatures and other elements that affect the formation of hurricanes.

Last year also had been quieter than initially feared, in sharp contrast with the record-setting 2005 Atlantic hurricane season when Katrina devastated New Orleans and part of the US Gulf coast.

"The seasonal hurricane forecasters certainly have a lot of explaining to do," said Max Mayfield, former director of the National Hurricane Center.

"The last couple of years have humbled the seasonal hurricane forecasters and pointed out that we have a lot more to learn before we can do accurate seasonal forecasts," he told The Miami Herald.

While there were fewer hurricanes than initially anticipated this year, two of those that formed in the Caribbean hit land with rare fury, packing maximum sustained winds of more than 249 kilometers (155 miles) per hour. That marked the first time on record that two Atlantic hurricanes made landfall at the topmost category five on the Saffir-Simpson intensity scale.

In August, Hurricane Dean killed at least 29 people in a rampage through the Caribbean and Mexico. The following month, Hurricane Felix killed about 150 people and wrought a trail of devastation along Nicaragua's impoverished Caribbean coast.