2005: Another Active Hurricane Season
Colorado State University team increases seasonal forecast.

Following an intense 2004 hurricane season, one of the most destructive on record for the United States, William Gray, Philip Klotzbach and the Colorado State University (CSU) forecast team have increased this year’s forecast and now call for significantly above-average Atlantic basin hurricane activity in 2005.

“All of the information we have collected and analyzed through March indicates that the 2005 Atlantic hurricane season will be an active one,” said Gray, who is in his 22nd year of forecasting Atlantic basin hurricane activity (see HP, Winter 2004, page 12). “We expect this year to continue the trend witnessed over the last decade of above-average hurricane seasons. We anticipate tropical cyclone activity in the Atlantic basin in 2005 will be about 135 percent of the long-term average. We also estimate the probability of U.S. major hurricane landfall to be about 140 percent of average.”

As detailed in a report released April 1 at CSU’s Fort Collins, CO, campus, Gray and his team anticipate that 13 named storms will form in the Atlantic basin between June 1 and November 30. Of these 13, seven are expected to develop into hurricanes and three are anticipated to evolve into intense, or major, hurricanes (Saffir/Simpson Category 3, 4, 5) with sustained winds of 111 mph or greater. The April 1 report was the first seasonal update provided by the forecast team since making its initial long-term forecast in early December (see HP, Winter 2005, page 6). The team’s December forecast called for 11 named storms, six hurricanes and three intense hurricanes. Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.

FORECAST NUMBERS MAY RISE

Gray and his team have been closely following the possible development of an El Nino event in the Pacific Ocean for the upcoming year, which would likely reduce the number of Atlantic hurricanes occurring during the 2005 season. After weeks of close observation, the team now believes that significant El Nino conditions for the upcoming summer and fall are less likely.

“If the next few months verify our beliefs about the lack of significant El Nino conditions, it is likely that we will be raising our forecast numbers in our coming May 31 and August 5 forecast updates,” said Klotzbach, atmospheric research scientist and forecast team member. “As it stands today, conditions in the Atlantic are very favorable for an active hurricane season.”

The Colorado State forecast team warns again this year of a considerably higher than average probability of at least one intense or major hurricane making landfall in the United States. According to the report, there is a 73 percent chance of at least one major hurricane hitting somewhere along the U.S. coastline in 2005 (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 53 percent (the long-term average is 31 percent). For the Gulf Coast, from the Florida Panhandle west to Brownsville, TX, the probability is 41 percent (the long-term average is 30 percent).

Gray’s team also foresees an above-average major hurricane landfall risk for the Caribbean. Major hurricanes account for about a quarter of all named storms, but on a normalized basis they typically cause about 80 to 85 percent of overall hurricane destruction.

NEW ERA

Gray believes that until last year, the United States had been very lucky over the past four decades in witnessing very few major hurricanes making landfall in Florida and along the East Coast.

“The 2004 hurricane season was an unusual year, and residents along the East Coast should not expect the high number of landfalling major hurricanes or the unprecedented level of destruction to be the norm for this or future years,” said Gray. “However, as last year made entirely too clear, citizens along the eastern seaboard should always be prepared for landfalling hurricanes.”

The last 10 years have witnessed 137 named storms, 77 hurricanes and 38 major hurricanes in the Atlantic basin. During that period, including 2004 when three major hurricanes made landfall, only six of the 38 major Atlantic basin hurricanes crossed the U.S. coastline. Based on historical averages, about one in three major hurricanes comes ashore in the United States.

“Over the last four decades the United States is still well behind the longer-term century average,” said Gray.

The storm seasons spanning 1995-2004 comprise the most active 10 consecutive hurricane years on record, and the Colorado State team believes that 2005 will follow this active trend. The forecasters believe that the United States is in a new, multi-decadal era for increased storm activity.

“We think that the United States has entered a new era of enhanced major hurricane activity reflective of the high activity during eight of the last 10 years,” said Klotzbach. “We expect this active tropical cyclone era to continue this year and to span the next two or three decades.”

The team has recently developed a Web page with extensive landfall probabilities for the Gulf and East Coast regions of the United States. In partnership with the GeoGraphics Laboratory at Bridgewater State College, a Web application has been created that displays landfall probabilities for 11 regions, 55 subregions and all 205 coastal and near-coastal counties from Brownsville, TX, to Eastport, ME. Probabilities of winds in the vicinity of a subregion and county as well as 50-year probabilities for winds of tropical storm force, hurricane force and intense hurricane force are also provided. The Web page is accessible at www.e-transit.org/hurricane. The site can also be accessed from the Colorado State University Tropical Meteorology Project home page at tropical.atmos.colostate.edu.