Cooler sea temperatures and a possible El Nino prompted the Colorado State University forecast team to reduce its Atlantic storm season prediction on Tuesday to 11 tropical storms, including five hurricanes.
In its April forecast, the noted CSU team founded by forecasting pioneer Bill Gray said the season would see 12 storms, including six hurricanes.
That forecast had been reduced from one issued in December, when the season was expected to produce 14 storms and seven hurricanes.
For the current season, which officially began on Monday and ends on November 30, two of the five hurricanes are expected to develop into "major" storms of Category 3 or higher on the Saffir-Simpson scale of hurricane intensity.
Major hurricanes have sustained winds above 110 mph (177 mph).
The long-term average for an Atlantic hurricane season is about 10 tropical storms, six hurricanes and two major hurricanes.
Gray's team said sea surface temperatures are cooler than normal in the tropical Atlantic, where hurricanes form. Cyclones draw energy from warm water, so cooler water temperatures can lead to fewer and less intense hurricanes.
The researchers also cited the possible development of an El Nino, the warm-water phenomenon in the eastern Pacific Ocean that can suppress hurricane activity in the Atlantic.
"We believe that there is a slightly greater chance of a weak El Nino developing this summer/fall than there was in early April," Gray said in a statement. "El Nino conditions would likely increase levels of vertical wind shear and decrease Atlantic hurricane activity."
The CSU team, now headed by researcher Phil Klotzbach, said there was a 48 percent chance of a major hurricane hitting the U.S. coast, compared to a long-term average of 52 percent.
Many hurricane forecasters have called for a quieter season than last year, which saw 16 tropical storms, including eight hurricanes.
It was a rough year for Haiti, where more than 800 people were killed in four tropical storms and hurricanes, and Cuba, which was hit by three major hurricanes and sustained at least $10 billion in damage.