Note to Editors: Forecast verification charts, the complete 2004 season verification report, as well as related research, detailed descriptions of forecast factors, previous forecasts and explanations of individual storms, are available on the Web at www.colostate.edu or http://typhoon.atmos.colostate.edu.
William Gray and Philip Klotzbach of the Colorado State University forecast team were on target again this year as they predicted a rough hurricane season for the Atlantic Basin as four intense hurricanes ravaged Florida and the Caribbean islands in August and September.
For the sixth consecutive year, the forecast team was on track with their seasonal hurricane forecast as highlighted in a summary report of 2004 Atlantic tropical cyclone activity released today. The report is available in its entirety on the Web at http://typhoon.atmos.colostate.edu.
Today’s report summarizes tropical cyclone activity in the Atlantic basin during the 2004 hurricane season and compares the team’s seasonal and monthly forecasts to what actually occurred.
The Colorado State team made their long-range seasonal forecast, which called for an active hurricane season, on Dec. 5, 2003, and then issued seasonal updates on April 2, May 28, Aug. 6, Sept. 3 and Oct. 1. In December 2003, the team predicted that 13 named storms, seven hurricanes and three intense hurricanes would form in the Atlantic basin in 2004. In their May 28 update, issued just before the official start of hurricane season, the team slightly adjusted their prediction to 14 named storms, eight hurricanes and three intense hurricanes. As the 2004 hurricane season comes to an end, the Atlantic basin has witnessed 14 named storms, eight hurricanes and six intense hurricanes.
"Overall, we consider 2004 a successful forecast year with regard to most of our forecast categories," Gray said. "However, although we called for an above-average season, there is no way that we or anyone else could have foreseen the number of Atlantic basin major hurricanes that developed during August and September or the large impact this activity would have on Caribbean and southeastern U.S. residents. This year had characteristics unlike any other year we have studied."
The team’s forecast numbers were on target with the number of named storms and hurricanes that occurred, but fell short in predicting the large amount of intense hurricanes that formed and concentrated in and around Florida in August and September.
"It is not the number of hurricanes in the Atlantic basin that was so unusual this year, but rather the rare combination of high major hurricane formation and very favorable hurricane steering conditions that drove so many storms from the deep tropics across the Caribbean and into Florida in such a concentrated period of six weeks," said Gray.
The team believes several major factors all came together and played a role in making the 2004 hurricane season very active with so many intense landfalling hurricanes. First, Atlantic sea-surface temperatures were anomalously warm throughout most of the basin – a factor shown to enhance tropical cyclone formation.
Additionally, strong low-level convergence, high low-level horizontal wind shear and low vertical wind shear combined perfectly to form so many major hurricanes. Associated with these favorable formation conditions were middle latitude wind patterns in the Western Atlantic that became arranged in a way to drive these major hurricanes from the deep tropics across the southeast corner of the United States.
"It was unusual to have these conditions come together so perfectly at one time, especially in a year where we also measured high Atlantic basin sea-level pressures and warm sea-surface temperatures in the tropical Pacific – generally indicators of reduced storm activity in the Atlantic basin, "Klotzbach said.
The report highlights how this year’s hurricanes had long westward tracks that were not typical of the tracks of most major hurricanes throughout the past decade. Throughout the active storm seasons of 1995-2003, the wind patterns tended to create a trough over the eastern North America coast. These trough conditions deflected westward moving hurricanes to the north before they were able to reach the U.S. coastline. In contrast, this year’s wind patterns created a ridge over the eastern North American continent and western Atlantic. This prevented recurvature to the north until the storms reached the longitudes of the southeast U.S., namely Florida. As a result, from 1995-2003, only three of the 32 major Atlantic basin hurricanes hit the United States; this year, four of the six major hurricanes made U.S. landfall.
"This year has been a once-in-a-lifetime kind of year," said Gray. "Although Floridians should always be prepared for landfalling hurricanes, they should not expect what we have experienced this year to become the norm for future years."
Florida was severely affected by four hurricanes in 2004, three of which were major storms (category 3-5). Hurricanes Frances (category 2), Jeanne (category 3), Ivan (category 3) and Charley (category 4) caused devastating damage in Florida. Although not making landfall, Hurricane Alex caused damage along the Outer Banks of North Carolina. In addition, tropical storms Bonnie, Gaston, Hermine, Ivan and Matthew made landfall along the Unites States coastline. Gray points out that the last time eight different tropical cyclones impacted the United States coastline was 1916. Gray’s team estimates that the four hurricane landfalls have caused over $50 billion in total damage, more than that of Hurricane Andrew in 1992.
Today’s report additionally highlights a variety of special characteristics of the 2004 hurricanes season, including the following.
– Twenty-three intense hurricane days were witnessed during the season; the average is five days per season. The 2004 season is tied with 1926 for the most intense hurricane days in one hurricane season.
– August and September were incredibly active storm months. August had eight named storms and three intense hurricanes, more than any other August on record. September had 17.75 intense hurricane days, more than any other September on record.
– The 2004 season is the first time four hurricanes (Charley, Frances, Ivan and Jeanne) made U.S. landfall since 1985.
– Three hurricanes (Charley, Frances and Jeanne) made landfall in Florida this year, the first time this has occurred since 1964.
– Two major hurricanes (Charley and Jeanne) made landfall in Florida in 2004, the first time this has happened since 1950.
– Charley became the first major hurricane to strike Florida since Opal in 1995. Charley is the first category 4 hurricane to strike Florida since Andrew in 1992.
– Ivan became the longest-lived intense hurricane on record, registering 10 intense hurricane days. The old record was held by the Miami Hurricane of 1926, which registered 9.25 days.
– Jeanne was the first major hurricane to strike Florida north of West Palm Beach and south of the Georgia/South Carolina border since 1893.
William Gray and his Colorado State team have provided seasonal Atlantic basin hurricane forecasts for the past 21 years. Until Gray began developing his forecast model in the early 1980s, there were no objective methods for predicting whether forthcoming hurricane seasons were likely to be active, inactive or near average.
"As the last six years indicate, we are making progress in better understanding and consequently improving seasonal prediction skill," Gray said. "With more research, this understanding will likely continue to improve, and we hope these forecasts will continue to be of assistance to coastal populations, emergency managers, insurance providers and others concerned about Atlantic basin hurricane activity."
Gray and his team are already working on their first seasonal forecast of the 2005 Atlantic basin hurricane season. This forecast report will be issued on Dec. 3, 2004, and will be available on the Web at http://typhoon.atmos.colostate.edu.
In addition to Gray and Klotzbach, other team members include William Thorson, Barbara Brumit, Amie Hedstrom and others.