Note to Editors: The complete forecast and detailed descriptions of forecast factors are available on the Web at www.colostate.edu or at http://typhoon.atmos.colostate.edu.
Following one of the most active August storm seasons on record – and as Florida braces for the impact of Hurricane Frances – William Gray and Philip Klotzbach of the Colorado State University hurricane forecast team are calling for another active storm month in September and the continuation of a well-above-average hurricane season.
"At the beginning of September, traditionally the most active month for hurricane activity, the United States has already been impacted by two tropical storms, Bonnie and Gaston, and two major hurricanes, Charley and Frances," said Gray. "Charley is being judged by many as the second most destructive hurricane behind 1992’s Andrew, but Frances, which will make landfall by Saturday, may bring more destruction to Florida than Charley did. It does not look good."
As detailed in a report issued this morning, the team’s September-only forecast calls for five named storms, three hurricanes and two major hurricanes, which would total approximately 85 percent of an average season’s storm activity. The October-only forecast, also issued today, predicts three named storms, one hurricane and no major hurricanes, slightly below the long-term average for October. The lower October forecast is due in large part to very warm equatorial sea surface temperatures in the central Pacific.
The team expects no significant storm activity in November.
August was a near-record month for tropical storm activity with eight named storms, four hurricanes and three intense hurricanes.
The long-term average number of named storms through August is 4.2, the average number of hurricanes is 2.4 and the average number of major hurricanes is 0.7. According to Gray, August alone witnessed 86 percent of the average season’s entire tropical storm activity, and climate predictors indicate September will also be well above average. Gray added that, in eight of the 10 most active Augusts on record, the September that followed also was a very active month for hurricanes.
Gray and his team had called for four named storms, three hurricanes and one intense hurricane in their early August forecast. "Although we expected above-average activity in August, we greatly underestimated the amount of activity that actually occurred," he said. "There is no way we could have anticipated the unusually high amount of the August activity. This will be a topic for future research."
Gray added that an important enhancing factor for August was the unusually strong positive sea-level temperature anomaly conditions in eastern tropical and mid-latitude Atlantic, and that the team undervalued the full influence of these conditions that are enhancing the month’s storm activities.
Due to the unusual amount of August Atlantic basin tropical activity, Gray and his team also increased their seasonal forecast. Today’s updated forecast calls for 16 named storms, eight hurricanes and five intense hurricanes, which would be approximately 185 percent of the average storm season. These numbers are up from the team’s early August 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.
"Many people are asking why we are seeing such an increased amount of landfalling hurricanes this season. A better question is why it has been so long since we have seen this amount of landfalling storms," said Gray. "In terms of long-term averages, we have been quite lucky for the past decade. However, we knew climatology would correct itself and this luck would eventually run out. It looks like this is the year."
Since August 1995, the Atlantic basin has experienced 35 intense or major hurricanes, of which only five have made or will soon make U.S. landfall, including this year’s Charley and Frances. However, the long-term average is about one in three major storms making landfall.
"The unfortunate landfalling hurricanes of Charley and Frances should not be taken as indicating that Florida is experiencing something new. The real surprise is that Peninsula Florida has experienced so few major hurricane strikes the during the past 38 years," said Gray.
During the 40-year period of 1926-1965, for example, South Florida received 14 major hurricane landfalls while the recent 38-year period of 1966-2003 saw only Andrew come ashore. According to Gray, part of the difference is due to the difference in global climate signals between those two periods. But another large part was just plain luck.
"We can never say exactly when or where it will happen, but we must continue to expect a great increase in landfalling major hurricanes such as we have seen this year," said Gray. "Unfortunately, with the large coastal population growth in recent decades, we need to anticipate hurricane-spawned destruction in coming years on a scale many times greater than what we have seen in the past."
Along with today’s updated probabilities, the team has updated the Landfall Probability Web site that 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 www.e-transit.org/hurricane, is the first publicly accessible 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. William Gray and Philip Klotzbach of the Colorado State University hurricane forecast team, with assistance from the GeoGraphics Laboratory at Bridgewater State
College in Massachusetts, launched the site in June.
August-only forecasts have now been made by the team for the last five seasons and September-only forecasts for the last three seasons. This is the second year that the team has issued an October-only forecast.
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 many detailed forecast factors, visit the Web at http://typhoon.atmos.colostate.edu.
Gray and his forecast team will issue seasonal updates of the 2004 Atlantic basin hurricane activity on Oct. 1 and issue a verification report in late November. In addition to Gray and Klotzbach, other team members include William Thorson, Barbara Brumit, Amie Hedstrom and others.