Despite independent and government forecasts that called for a very active 2006 Atlantic hurricane season, the resulting slightly below-average activity — which was welcomed by the southern U.S. coastline as well as Gulf of Mexico oil and gas producers — was blamed on a late-developing El Nino and increased dryness in the tropical Atlantic, according to William Gray and Philip Klotzbach of the Colorado State University forecast team.
Much like other forecasters, the respected Gray and Klotzbach team in December, April and June forecasts had predicted that 2006 hurricane season would have well above average activity. In the seven years prior to 2006, the forecast team correctly predicted above- or below-average activity in its June hurricane forecasts.
“A variety of factors interact with each other to cause year-to-year and month-to-month hurricane variability,” said Klotzbach, lead author on the forecasts. “It is impossible to understand how all these processes interact with each other to100% certainty. Continued research should help us better understand these complicated atmospheric/oceanic interactions.”
Gray pointed out that in addition to less-than-expected activity, the lack of landfalling hurricanes also was unique. “The 2006 Atlantic basin hurricane season was much less active than the 2004 and 2005 seasons, but 2006 was also atypical in that there were no landfalling hurricanes along the U.S. coastline this year,” said Gray, who has led the forecasting team at Colorado State for 23 years. “This is the first year [since 2001] that there have been no landfalling hurricanes along the U.S. coastline…, and this is only the 11th year since 1945 that there have been no U.S. landfalling hurricanes.”
The Colorado State team made its long-range seasonal forecast, which called for an above-average hurricane season, on Dec. 6, 2005, and then issued seasonal updates on April 4, May 31, Aug. 3, Sept. 1 and Oct. 3 (see NGI, Oct. 9). On May 31, just before the official start of hurricane season, the team called for 17 named storms, nine hurricanes and five intense hurricanes. By August, the team updated and lowered its forecast to reflect the downward trend caused largely by the late arrival of El Nino.
The 2006 season ended up seeing only nine named storms, five hurricanes and two major hurricanes, which contrasted sharply with 2005. The 2005 season witnessed 27 named storms, 15 hurricanes and seven intense hurricanes — activity that Colorado State forecasters have called an anomaly.
“The record number of tropical cyclones in 2005…should not be taken as an indication of something beyond natural processes,” Gray said. “There have been several other years with comparable hurricane activity to 2005,” Gray added, pointing to 1933, which experienced 21 named storms in a year when there was no satellite or aircraft data.
The nine named storms in 2006 were the fewest named storms to form in the Atlantic since 1997, when only seven named storms formed. The five hurricanes were the fewest hurricanes to form in the Atlantic since 2002, when four hurricanes formed. And 1997 was the most recent year to have fewer than two major hurricanes form (one named Erika). This year was the first year with no Category 4-5 hurricanes in the Atlantic since 1997.
“We continue to modify our seasonal predictions based on the information we obtain every year,” Gray said. “With more research, this understanding will likely continue to improve, and we hope these forecasts will continue to be of assistance to coastal populations, emergency managers, insurance providers and others concerned about Atlantic basin hurricane activity.”
Gray and his team are already working on their first seasonal forecast of the 2007 Atlantic basin hurricane, which will be issued on Dec. 8, 2006 and will be available on the Web at https://hurricane.atmos.colostate.edu.
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