Note to Editors: The complete hurricane forecast report is available at http://newsinfo.colostate.edu/index.asp. The completed forecast, charts and previous forecasts will be available after 8 a.m. MDT at http://hurricane.atmos.colostate.edu.
The Colorado State University hurricane team today slightly reduced the number of storms expected to form in the Atlantic this season based on slightly cooler sea surface temperatures over the tropical Atlantic.
However, researchers Philip Klotzbach and William Gray still expect a much more active season than the typical season between 1950 and 2000. They’re calling for a total of 15 named storms for the entire hurricane season with eight becoming hurricanes and four becoming intense hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.
Only two named storms have been observed so far this season (the team does not include subtropical storm Andrea, which formed off the southeastern U.S. coastline on May 9 and was never classified as a tropical storm by the National Hurricane Center).
"The number of storms that formed during June and July isn’t relevant to this newest forecast – we’ve lowered our forecast from our May predictions because of slightly less favorable conditions in the tropical Atlantic," Klotzbach said. "Sea surface temperature anomalies have cooled across the tropical Atlantic in recent weeks, and there have been several significant dust outbreaks from Africa, signifying a generally stable air mass over the tropical Atlantic."
ENSO conditions have trended slightly cooler over the past few weeks. The forecast team expects generally cool to weak La Nina conditions to be present during the upcoming hurricane season.
The forecast is down slightly from the team’s late May prediction of 17 named storms, nine hurricanes and five intense hurricanes. The long-term average is 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.
This is the Colorado State team’s 24th year of issuing early August forecasts. The team has gone in the right direction (above or below) relative to the average season in 21 of 23 years for named storms and 17 of 23 years for hurricanes.
"We expect the Atlantic basin tropical storm season will be active with activity that is about 160 percent of the long-term average," said Gray. "As always, residents should take precautions during hurricane season and be prepared."
The hurricane forecasters on Friday also issued additional tropical cyclone activity forecasts for the individual months of August, September and a combined October-November prediction. The monthly forecasts use different parameters than the seasonal forecasts to predict storm activity within shorter time periods and aid with the seasonal predictions.
For the month of August, the team expects three named storms, two hurricanes and one intense hurricane for the Atlantic basin. For September, the team predicts five named storms, four hurricanes and two intense hurricanes. For October-November, Klotzbach and Gray predict five named storms, two hurricanes and one intense hurricane.
"Typically, the end of the Atlantic basin hurricane season is governed by rising values of vertical wind shear," Gray said. "Since we expect generally cool to weak La Nina conditions this year, the end of the Atlantic basin hurricane will likely be extended this year."
"The same factors that make individual months active or inactive are often not the same factors that can make the entire season active or inactive," said Klotzbach. "We are continually improving our forecasts to provide people with specific monthly hurricane forecasts and specific landfall probability forecasts."
Along with today’s updated probabilities, the team has updated the Landfall Probability Web site, which provides probabilities of tropical storm-force, hurricane-force and intense hurricane-force winds making landfall in specific locations along the U.S. East and Gulf coasts within a variety of time periods.
Probabilities are available for 11 regions, 55 sub-regions and 205 individual counties along the U.S. coastline from Brownsville, Texas, to Eastport, Maine. The Web site, available to the public at http://www.e-transit.org/hurricane, is an Internet tool that adjusts landfall probabilities for regions, sub-regions and counties based on the current climate and its projected effects on the upcoming hurricane season. Klotzbach and Gray, with assistance from the GeoGraphics Laboratory at Bridgewater State College in Massachusetts, launched the site in 2004.
The Colorado State forecast team continues to warn of the considerably higher-than-average probability of at least one intense (or major) hurricane making landfall in the United States this year. According to today’s forecast, there is a 68 percent chance of an intense hurricane hitting somewhere along the U.S. coastline during the remainder of the 2007 hurricane season (long-term average is 52 percent). For the U.S. East Coast, including the Florida Peninsula, the probability of an intense hurricane making landfall is 43 percent (long-term average is 31 percent).
For the Gulf Coast from the Florida Panhandle westward to Brownsville, Texas, the probability is 44 percent (the long-term average is 30 percent).
The forecast also calls for above-average major hurricane landfall risk in the Caribbean.
Gray said the United States has been fortunate over the past few decades in experiencing only a few major hurricanes making landfall in Florida and along the East Coast. 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 3.5 major hurricanes comes ashore in the United States.
In 2004 and 2005, 13 major hurricanes formed in the Atlantic basin – seven of them striking the U.S. coast. In 2004, Hurricanes Charley, Ivan and Jeanne made landfall followed in 2005 by Dennis, Katrina, Rita and Wilma.
"Those years were anomalies," Gray said. "We’re in an active cycle in the Atlantic basin that is expected to last another 15 to 20 years. We believe this is part of a natural ocean cycle and is not the result of human-induced global warming."
The team works to improve forecast methodologies based on a variety of climate-related global and regional predictors.
"We are continually making progress in improving statistical hurricane forecasting techniques and in better understanding why there is such variability in month-to-month and year-to-year Atlantic basin hurricane activity," said Klotzbach. "Our ongoing forecast research is allowing us to continually improve hurricane prediction skill."
The team will issue seasonal updates of the 2007 Atlantic basin hurricane activity on Sept. 4 and Oct. 2. Included will be separate forecasts of September-only and October-November only Atlantic basin tropical cyclone activity.