The hurricane forecast team at Colorado State University are trimming their May tropical predictions, but not by much. Researcher Philip Klotzbach said Friday morning, Aug. 3, that lower than expected sea surface temperatures and desert sand get the credit.

“The ocean waters have cooled slightly to about average, and we’ve seen a decent amount of stable dry air during June and July,” he said.

But Klotzbach and forecast co-author William Gray still expect a much more active year than the typical season between 1950 and 2000. They project a total of 15 named storms, with eight becoming hurricanes and four becoming intense hurricanes (Saffir/Simpson Scale category 3-5) with sustained winds of 111 mph or more.

Only two named storms have formed so far this season. The CSU team doesn’t include subtropical storm Andrea in the tally. The disturbance, which formed off the southeastern U.S. coast May 9, was never classified as a tropical storm by the National Hurricane Center.

Klotzbach said the previous storms aren’t really relevant to the latest forecast anyway. The sluggish start to the 2007 season is simply the result of less favorable conditions in the tropical Atlantic, he said. In addition to cooler sea surface temperature anomalies during the early summer, several significant dust storms from the Sahara Desert came into play.

Klotzbach said, “You have a period of Saharan dust outbreaks, then you won’t have them for a while. It kind of pulses. More dust reflects radiation back to space. But, the dust has been dissipating and the water warming the last couple of weeks.”

The forecast team also expects generally cool to weak La Niña conditions to be present during the current hurricane season. That could also increase the number of named storms.

The new CSU forecast replaces the team’s late May prediction of 17 named storms, nine hurricanes and five intense hurricanes. The long-term average is 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.

Klotzbach said the Atlantic basin typically doesn’t experience its second named storm until the first week in August, which is considered the first of three peak months.

“We expect the Atlantic basin tropical storm season will be active with activity that is about 160 percent of the long-term average,” Gray stated in a press release. “As always, residents should take precautions during hurricane season and be prepared.”

Klotzbach concurred. He said, “Even if it’s an inactive season, all it takes is one storm tracking over your neighborhood to make it an active season. So people living on the Gulf Coast shouldn’t let down their guard.”

The CSU forecasters have also issued more tropical cyclone activity forecasts for the individual months of August, September and a combined October-November prediction. The monthly forecasts use different parameters than the seasonal forecasts to predict storm activity within shorter time periods and aid with the seasonal predictions.

For August, the team expects three named storms, two hurricanes and one intense hurricane for the Atlantic basin. For September, the team predicts five named storms, four hurricanes and two intense hurricanes. For October-November, Klotzbach and Gray predict five named storms, two hurricanes and one intense hurricane.

“Typically, the end of the Atlantic basin hurricane season is governed by rising values of vertical wind shear,” Gray noted. “Since we expect generally cool to weak La Niña conditions this year, the end of the Atlantic basin hurricane will likely be extended this year.”

The CSU forecast team continues to warn of the considerably higher-than-average probability of at least one intense hurricane making landfall in the United States this year. According to the Friday forecast, there is a 68 percent chance of an intense hurricane hitting somewhere along the U.S. coast during the remainder of the 2007 season (long-term average is 52 percent). For the U.S. East Coast, including the Florida Peninsula, the probability of an intense hurricane making landfall is 43 percent (long-term average is 31 percent).

For the Gulf Coast from the Florida Panhandle westward to Brownsville, Texas, the probability is 44 percent (the long-term average is 30 percent).

The forecast also calls for above-average major hurricane landfall risk in the Caribbean.

Between 1995 and 2003, 122 named storms, 69 hurricanes and 32 major hurricanes formed in the Atlantic basin. During that period, only three of the 32 major hurricanes — Opal, Bret and Fran — crossed the U.S. coastline. Based on historical averages, about one in 3.5 major hurricanes comes ashore in the United States.

In 2004 and 2005, 13 major hurricanes formed in the Atlantic basin, with seven of them striking the U.S. coast. In 2004, hurricanes Charley, Ivan and Jeanne made landfall followed in 2005 by Dennis, Katrina, Rita and Wilma.

“Those years were anomalies,” Gray added. “We’re in an active cycle in the Atlantic basin that is expected to last another 15 to 20 years. We believe this is part of a natural ocean cycle and is not the result of human-induced global warming.”

The team will issue seasonal updates of the 2007 Atlantic basin hurricane activity on Sept. 4 and Oct. 2.