By Michael Christie MIAMI, Nov 17 (Reuters) - The noted hurricane forecasting team led by Dr. William Gray at Colorado State University has not missed by this much in a long time. Before the Atlantic 2006 hurricane season started, Gray and his protege Philip Klotzbach predicted it would be well above average. Instead, it has been slightly below average as the Nov. 30 end of the season draws near -- and a mere whimper compared with the destruction caused by monster hurricanes like Katrina, Rita and Wilma in 2005. In a sort of mea culpa issued by the CSU forecasting team on Friday, Gray and Klotzbach said the late development of a hurricane-supressing El Nino phenomenon, and unusually dry conditions over the Atlantic, "complicated" their forecast. It was the first time in eight years that they had failed to predict accurately whether a season would be busier than average, they said. "A variety of factors interact with each other to cause year-to-year and month-to-month hurricane variability," Klotzbach said in the end-of-season report. "It is impossible to understand how all these processes interact with each other to 100 percent certainty." The CSU team formed by Gray and now headed by Klotzbach is regarded as a leader in the field of long-range hurricane forecasting and their predictions are eagerly awaited -- and bet on -- by traders in affected markets, such as energy and insurance. On May 31 they predicted that there would be 17 storms this year, of which nine would be hurricanes. In the end, the 2006 season managed to produce nine tropical storms, of which five became hurricanes. None of the hurricanes hit the United States. There are still two weeks to go, but the U.S. National Hurricane Center in Miami says there is little sign of any action in the Atlantic. The Colorado State team was far from alone in predicting that 2006 would be more active than an average year, in which the Atlantic can be expected to spawn 10 tropical storms, of which six will strengthen into hurricanes. No one foresaw what happened in 2005 either, when 28 storms swarmed out of the Atlantic and 15 became hurricanes with winds of at least 74 miles per hour (119 km per hour). Among them, Katrina killed 1,500 people along the U.S. Gulf Coast and swamped New Orleans, while Wilma became the strongest Atlantic hurricane ever observed. Long-range hurricane forecasting, like all long-range weather predictions, remains a complex and error-prone task, experts say. Yet hurricane experts also say the failure of 2006 to live up to expectations had left them scratching their heads. "I think there is some mystery," said James Elsner, a geography professor at Florida State University who has conducted research on hurricanes. The unexpected formation of the El Nino phenomenon in the eastern tropical Pacific was probably a chief factor. An unusual warming of Pacific waters, El Nino years tend to create unfavorable conditions over the Atlantic for the formation of hurricanes, which are fragile constructs despite their size and ferocity. The experts also say an unusual amount of sub-Saharan dust in the atmosphere over the Atlantic may have deprived potential storms of the moisture they use as fuel. But there are probably other factors at work that have yet to be identified. In any case, hurricane experts urge people not to let their guard down. Elsner noted that storms still formed this year even in unfavorable conditions. "We saw an average season even in the face of fairly hostile thermodynamics and shear -- indicative of the fact that if the sea surface temperatures continue to warm, we are going to see more strong storms," Elsner said.
