While Tropical Storm Ernesto continued to soak the Mid-Atlantic Friday, one prominent hurricane forecasting team was slashing its expectations for the 2006 season for a second time in a month. In the downgrade, Colorado State University forecasters William Gray and Philip Klotzbach said they now expect there to be fewer hurricanes in the Atlantic than during a normal season.

Based on changing climate signals and below-average activity in the first third of the season, the team is now calling for a total of 13 named storms to form in the Atlantic basin this season. Of these, five are predicted to become hurricanes and two are anticipated to evolve into intense hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater. The new forecast is down from the team’s August forecast of 15 named storms, seven hurricanes and three intense hurricanes (see Daily GPI, Aug. 4). The long-term average is 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.

“We predict September and October will exhibit characteristics of a more average year based on the activity so far this season and climate signals through August,” Klotzbach said. “Current conditions in the Atlantic indicate that we will now see a slightly below-average hurricane season with far less activity than was experienced in each of the last two years.”

These changes include drier tropical Atlantic mid-level moisture fields, high levels of West African dust over the Atlantic, and a warmer eastern equatorial Pacific, indicating a potential El Nino event this fall. Gray and Klotzbach said that unlike 2005 when two major hurricanes — Dennis and Emily — developed and intensified in the tropical Atlantic and Caribbean, no hurricane activity occurred in the deep tropics during June and July 2006. August 2006 had about average named-storm activity, but the amount of intense activity was well below-average. Only one hurricane — Ernesto — formed during August — and lasted less than one day due to interaction with land. On average, about six hurricane days occur during August.

Looking at the next two months, the CSU team said the September-only forecast calls for five named storms, three hurricanes and two major hurricanes, which is slightly above-average for September. The October-only forecast calls for two named storms, one hurricane and no major hurricanes, which is below average. “Despite the lower predictions, residents living along the U.S. coastline should always be prepared for major storms,” Gray said.

Until 2004 and 2005, Gray and Klotzbach said the United States has been fortunate over the past few decades in experiencing only a few major hurricanes making U.S. landfall. 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 three major hurricanes that forms in the Atlantic basin comes ashore in the United States. But in the past two years, 13 major hurricanes formed in the Atlantic basin — seven of them striking the U.S. coast, the team said.

“For many years, we have been warning of the return of major hurricane landfall events similar to what was experienced in the 1940s through the 1960s,” Klotzbach said. “We also warned that destruction was likely to be higher than was previously experienced due to increased coastal population and wealth per capita.”

“We recommend that there not be too much read into the last two hurricane seasons of 2004-2005,” Gray said. “The activity of these two years was unusual but well within natural bounds of hurricane variation. This is how nature sometimes works.”

The team said it will issue a seasonal update and an updated monthly forecast for October 2006 Atlantic basin hurricane activity on Oct. 3.

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