Active Atlantic Hurricane Season Forecast for 2007

FORT COLLINS, Colorado, December 8, 2006 (ENS) - No hurricane touched the U.S. coastline in 2006, but that unusual respite is not likely to be repeated next year, according to the early season forecast issued today by Colorado State University's forecasting team.

The El Nino weather conditions that led to a quiet Atlantic hurricane season in 2006 will probably dissipate by next summer, leading to above-average hurricane activity for 2007, said Philip Klotzbach, William Gray and their colleagues at Colorado State.


William Gray, left, and Philip Klotzbach lead the hurricane forecasting team at Colorado State University. (Photo courtesy CSU)
"The 2007 Atlantic hurricane season is expected to be more active than the average 1950-2000 season," Klotzbach said. "However, this is an early prediction. One of the important questions for the upcoming season is whether El Nino conditions will continue through 2007."

The term El Nino refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea surface temperatures across the central and east-central equatorial Pacific Ocean. Its opposite is the cooler weather pattern known as La Nina.

The United States faces another active Atlantic basin hurricane season in 2007, the forecasters said, but with likely fewer landfalling intense hurricanes than in 2005 - the costliest, most destructive hurricane season ever.

The team's first extended-range forecast for the 2007 hurricane season anticipates 14 named storms forming in the Atlantic basin between June 1 and November 30.

Seven of those 14 storms are predicted to become hurricanes, and of those seven, three are expected to develop into intense or major hurricanes ranked Category 3, 4, or 5 on the Saffir/Simpson scale. Those categories cover hurricanes with sustained winds of 111 miles per hour or greater.

The Colorado State 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.


Hurricane Rita makes landfall at the Texas-Louisiana border on the U.S. Gulf Coast, September 23, 2005. The fourth-most intense Atlantic hurricane ever recorded, Rita caused $10 billion in damage. (Photo courtesy NOAA)
Late-developing El Nino conditions contributed to a calmer 2006 hurricane season. But Klotzbach notes that seven of eight seasons following El Nino conditions in an active Atlantic multi-decadal period were active Atlantic hurricane seasons.

The NOAA Climate Prediction Center said Thursday that El Nino conditions are likely to continue through May 2007.

But Gray and the Colorado State 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 Nina conditions next summer - 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, Gray said. The average of these four seasons had well above-average activity.

Scientists are divided on the issue of whether global warming is raising sea surface temperatures enough to increase the incidence of hurricanes. Gray says global warming is not to blame.

"Recent or projected Atlantic hurricane activity is likely not linked to human-induced global warming," he said today.

"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.

No hurricanes hit the U.S. coastline in 2006 - only the 11th time that has occurred since 1945.

In contrast, the 2005 season witnessed 27 named storms, 15 hurricanes and seven intense hurricanes.

Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.

"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," he said.


The strongest El Nino on record causes California's Russian River to overflow its banks, March 1998.(Photo courtesy NASA)
Meanwhile, storminess and wetter than average conditions can be expected over the next one to three months across the southern tier of the U.S. from central and southern California across the southwest to Texas and across the Gulf Coast to Florida and the southeast.

The prediction of increased precipitation is due to a strenthening El Nino weather pattern in the tropical Pacific Ocean, according to the National Oceanic and Atmospheric Administration.

"Evolving current conditions in the equatorial Pacific are likely to cause a substantial increase in sea surface temperature along the west coast of South America in late December 2006 and January 2007," said Vernon Kousky, PhD, NOAA's lead El Nino forecaster.

"At about the same time, rainfall is expected to increase over the warm waters in the central equatorial Pacific, thus setting the stage for typical El Nino effects over the U.S. during January through March 2007," Kousky said.

El Nino weather patterns are typically associated with drier than average conditions in the Ohio and Tennessee Valleys and in the northern Rockies.