WSI raised the number of named storms expected to 15 from 14 and the number of hurricanes to nine from eight.

WSI's forecast for four intense hurricanes was unchanged from the previous forecast, issued in June.

Oil markets closely monitor hurricane forecasts after the severe damage caused to US Gulf Coast oil production and refining facilities by hurricanes Katrina and Rita in 2005.

This season has already produced four named storms, including Tropical Storm Dolly, now pushing through the western Gulf of Mexico on a track toward the Texas-Mexico border.

The US government's Minerals Management Service said on Tuesday that oil companies had shut roughly 5 percent of the Gulf of Mexico's oil and natural gas production as a precaution due to Dolly.

"Since 1995, most tropical seasons have been more active than the long-term averages, due to warmer Atlantic Ocean temperatures. We do not see any reason why this active regime will not continue in 2008," Crawford said.

"The recent La Nina event should leave behind a wind shear environment that is favorable for the development of tropical systems in the summer and fall of 2008."

The 2008 forecast numbers are significantly higher than the average for the period from 1950 to 2007 of 9.7 named storms, 5.9 hurricanes and 2.3 intense hurricanes.

"The relatively early occurrence of the first intense hurricane, Bertha, is also usually an omen for a very active season," Crawford said.

Tropical Storm Bertha formed in early July and later strengthened into a hurricane.

The Atlantic hurricane season lasts from June 1 through Nov. 30. (Reporting by Rebekah Kebede)