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seasonal
forecast
Active 2007 Hurricane Season
CSU forecasters predict seven hurricanes, but it still depends on El Nino.
The El Niño conditions that led to a quiet hurricane season in 2006 are likely to dissipate by this summer leading to above-average hurricane activity for 2007, according to the early season forecast issued in December 2006 by Colorado State University’s (CSU) forecasting team, Fort Collins, CO.
The first extended-range forecast for the 2007 hurricane season, written by Philip Klotzbach, William Gray and the CSU forecast team, anticipates 14 named storms forming in the Atlantic basin between June 1 and November 30. Seven of the 14 storms are predicted to become hurricanes; and of those seven, three are expected to develop into intense or major hurricanes (Category 3, 4 or 5) with sustained winds of 111 mph or greater.
“The 2007 Atlantic hurricane season is expected to be more active than the average 1950-2000 season,” said Klotzbach. “However, this is an early prediction. One of the important questions for the upcoming season is whether El Niño conditions will continue through 2007.”
Late-developing El Niño conditions contributed to a calmer 2006 hurricane season, but Klotzbach notes that seven of eight seasons following El Niño conditions in an active Atlantic multi-decadal period were active Atlantic hurricane seasons.
ACTIVE CYCLE
There likely will be fewer landfalling intense hurricanes this season than in 2005—the costliest, most destructive hurricane season ever—but the CSU hurricane forecast team predicts a 64 percent chance that at least one major hurricane will make landfall on the U.S. coastline in 2007. The long-term average probability is 52 percent.
For the U.S. East Coast, including the Florida Peninsula, the probability of an intense hurricane making landfall is 40 percent (the long-term average is 31 percent). For the Gulf Coast from the Florida Panhandle west to Brownsville, TX, the probability is 40 percent (the long-term average is 30 percent).
Florida and the Gulf Coast were ravaged by four landfalling hurricanes in 2004 and 2005. Hurricanes Charley, Frances, Ivan and Jeanne caused devastating damage in 2004 followed by Dennis, Katrina, Rita and Wilma in 2005.
Gray has said that it would be statistically unlikely that two years in the near-future hurricane seasons would have the number of U.S. landfalling major hurricanes seen in 2004 and 2005.
No hurricanes hit the U.S. coastline in 2006—only the 11th time that has occurred since 1945. “Despite a fairly inactive 2006 hurricane season, we believe that the Atlantic basin is in an active hurricane cycle,” Gray said. “This active cycle is expected to continue for another decade or two at which time we should enter a quieter Atlantic major hurricane period like we experienced during the quarter-century periods of 1970-1994 and 1901-1925.”
EFFECT OF GLOBAL WARMING
The first 2007 extended-range forecast is the teams’ 24th hurricane forecast. It is based on the premise that global oceanic and atmospheric conditions—such as El Niño, sea surface temperatures and sea level pressure—that preceded active or inactive hurricane seasons in the past provide meaningful information about similar trends in future seasons.
For 2007, Gray and the hurricane forecast team expect continued warm tropical and north Atlantic sea-surface temperatures, prevalent in most years since 1995, as well as neutral or weak La Niña conditions—a recipe for greatly enhanced Atlantic basin hurricane activity. These factors are similar to conditions that occurred during the 1952, 1958, 1966 and 2003 seasons. The average of these four seasons had well above-average activity.
The U.S. landfall of major hurricanes in 2005 and the four Florida landfalling hurricanes of 2004 raised questions about the possible role that global warming played in these two unusually destructive seasons.
“Recent or projected Atlantic hurricane activity is likely not linked to human-induced global warming,” Gray said.
“Despite the global warming of the sea surface that has taken place over the last three decades, the global numbers of hurricanes and their intensity has not shown increases in recent years except for the Atlantic,” Gray said.
There have been similar past periods (1940s-1950s) when the Atlantic was just as active as in recent years. For instance, when we compare Atlantic basin hurricane numbers over the 15-year period (1990-2004) with an earlier 15-year period (1950-1964), we see no difference in hurricane frequency or intensity even though the global surface temperatures were cooler and there was a general global cooling during 1950-1964 as compared with global warming during 1990-2004. |
