William Gray and Colorado State Team Increase Forecast, Expect Very Active Hurricane Season in 2005

Note to Editors: The complete hurricane forecast, a detailed description of forecast factors, downloadable broadcast-quality audio clips and video clips are available on the Web at www.colostate.edu.

In their final update before the official start of the hurricane season tomorrow (June 1), William Gray, Philip Klotzbach and the Colorado State University forecast team have increased their early-season predictions and call for a very active Atlantic basin hurricane season in 2005.

"We foresee a well above-average hurricane season for the Atlantic basin as well as an above-average probability of U.S. major hurricane landfall in 2005," said Gray. "We have adjusted our forecast upward from our early April forecast and now expect tropical cyclone activity to be about 170 percent of the average seasonal activity."  

As detailed in today’s updated Atlantic seasonal hurricane activity forecast (May 31), Gray and his colleagues call for a total of 15 named storms to form in the Atlantic basin this year. Of these, eight are predicted to become hurricanes and four are anticipated to evolve into intense hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater. These forecasts numbers are up from the team’s April 1 forecast of 13 named storms, seven hurricanes and three intense hurricanes. The long-term average is 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.

"We have increased the forecast from our early April prediction due to continued Atlantic Ocean warming and a decreased likelihood of the development of an El Nino this summer and fall," Klotzbach said. "Conditions in the Atlantic are very favorable for an active hurricane season and are expected to trump some of the unfavorable non-Atlantic climate signals."  

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The Colorado State forecast team also warns 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 77 percent chance of an intense hurricane hitting somewhere along the U.S. coastline in 2005 (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 59 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 team also calls for above-average major hurricane landfall risk in the Caribbean.

On a long-term basis, major hurricanes account for about a quarter of all named storms, but when normalized for population, inflation and wealth per capita, those hurricanes cause about 85 percent of all tropical cyclone-spawned destruction.

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. This was due to a combination of past climate signals that did not favor major hurricane development or the tracking of these storms across the United States. In addition, there were several lucky near-miss events. Even last year, the United States was fortunate that the four hurricanes that caused considerable damage and destruction did not come ashore in major population centers.

"Residents along the East Coast should not expect the typical U.S. hurricane landfalling conditions of the last 40 years to be the norm for the next few decades," said Gray. "As last year made very 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 where 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.

The storm seasons spanning 1995-2004 comprised 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.

The team attributes this last decade increase (as well as the increase from the 1930s through the 1960s) in major hurricane activity to be a consequence of the strengthening of the Atlantic Ocean

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thermohaline circulation. From historical records, the thermohaline circulation is known to oscillate back-and-forth on a time scale of about 40-60 years. This oscillation is believed to be driven by alterations in Atlantic Ocean salinity variations.  

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

Gray and Klotzbach 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, Texas, to Eastport, Maine. Probabilities of winds in the area 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 http://www.e-transit.org/hurricane. The site can also be accessed from the Colorado State University Tropical Meteorology Project homepage at http://hurricane.atmos.colostate.edu/.

The Colorado State forecast team does not attribute changes in recent or projected Atlantic basin hurricane activity to human-induced global warming.  

Gray and his team will be issuing seasonal updates of their 2005 Atlantic basin hurricane activity forecast on Aug. 5, Sept. 2 and Oct. 3. The August, September and October seasonal updates also will include the team’s new August-only, September-only and October-only monthly hurricane forecasts.

Gray and his team continuously work to improve their forecast methodologies based on a variety of climate-related global and regional predictors. For a detailed description of the forecast factors, visit the Web at http://hurricane.atmos.colostate.edu/.

"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," Gray said. "Our ongoing forecast research is allowing us to continually improve our understanding and consequently our hurricane prediction skill."