The noted Colorado State University hurricane research team yesterday raised the number of tropical storms and hurricanes it expects to form in the upcoming Atlantic storm season, Reuters has reported.

The team founded by forecasting pioneer Bill Gray increased its outlook by two tropical storms to 15, and by one hurricane to eight, compared with a long-term average of around 10 and six, respectively, for a storm season.

"Current oceanic and atmospheric trends indicate that we will likely have an active Atlantic basin hurricane season," said Mr. Gray in a statement.

Of the eight hurricanes predicted by the forecasters for the six-month season starting on June 1, four were forecast to become major storms with winds of at least 111 mph (178 kph). Major, or intense, storms, which rank from Category 3 to Category 5 on the five-step Saffir-Simpson scale of hurricane intensity, are the most destructive.

"Based on our latest forecast, the probability of a major hurricane making landfall along the US coastline is 69 percent compared with the last-century average of 52 percent," said Gray protege Phil Klotzbach, who now leads the CSU team.

"We are calling for a very active hurricane season this year, but not as active as the 2004 and 2005 seasons."

The CSU team said the conditions favouring an active hurricane season in 2008 included a continuing though likely weakening La Nina in the Pacific, warm sea surface temperatures in the tropical eastern Atlantic and the likelihood of weak trade winds.

The La Nina weather phenomenon — an unusual cooling in the Pacific — tends to result in conditions that favour hurricanes in the Atlantic, while its opposite, El Nino, creates vertical wind shear that tears nascent hurricanes apart.

Mr. Gray's team said it expected to see a moderation in La Nina conditions but did not expect a transition to an El Nino event during the hurricane season.

It said in its report that it had not raised the expectation for the number of hurricanes as high as some of its calculations had suggested it do, because of uncertainty over how long La Nina conditions would persist.