Note to Reporters: The full verification report of 79 pages and a chart showing the predictions vs. observed storms are available with the news release at http://www.news.colostate.edu/ and at http://hurricane.atmos.colostate.edu/. The report includes an extensive discussion of the climate features that caused the 2010 Atlantic basin hurricane season to be as active as it was.
The Colorado State University hurricane forecast team accurately predicted well above-average hurricane activity for the Atlantic basin for 2010, according to its seasonal verification report issued today.
A combination of very warm tropical Atlantic sea surface temperatures, low sea level pressures and the onset of La Nina contributed to cause this season to have an unusually large number of hurricanes and major hurricanes.
The report summarizes tropical cyclone activity in the Atlantic basin during the 2010 hurricane season and compares the team’s seasonal and two-week forecasts to what actually occurred.
The Colorado State team of Phil Klotzbach and William Gray made its long-range seasonal forecast, which called for an above-average hurricane season, in early December 2009 and issued seasonal updates on April 7, June 2 and Aug. 4, 2010, all of which called for increased levels of hurricane activity.
Just as hurricane season began in June, the team called for 18 named storms, 10 hurricanes and five major (Category 3-4-5) hurricanes.
Observed were 19 named storms, 12 hurricanes and five major hurricanes. Since 1944, only 1995 (19) and 2005 (28) have had as many named storms.
The team bases its annual forecasts on 60 years of previous data that includes factors such as Atlantic sea surface temperatures and sea level pressures, levels of vertical wind shear (the change in wind direction with height), El Nino (an anomalous warming of waters in the central and eastern tropical Pacific) and other factors.
“Our Atlantic basin seasonal hurricane forecasts correctly predicted a very active hurricane season,” Klotzbach said. “We were pleased that our newly designed statistical models were able to correctly predict this very active season.”
Landfall statistics captured in the report:
• No hurricanes made landfall along the Florida Peninsula and East Coast. This marks the fifth year in a row with no hurricane landfalls along this portion of the U.S. coastline. This is the first time since reliable U.S. records began in 1878 that no hurricanes have made landfall along the Florida Peninsula and East Coast in a five-year period.
• This is the first time in recorded history that as many as 12 hurricanes have occurred in the Atlantic basin without a U.S. landfall. Prior to that record, at least two hurricanes made landfall in the United States when a minimum of 10 hurricanes occurred in the Atlantic basin.
• No major hurricanes made U.S. landfall this year. Following seven major hurricane landfalls in 2004-2005, the nation has not witnessed a major hurricane landfall in the past five seasons. The five consecutive years between 1901-1905 and 1910-1914 have been the only other consecutive five-year periods with no major U.S. hurricane landfalls.
• Only one tropical storm made U.S. landfall this year (Bonnie). We have not had a hurricane landfall since Hurricane Ike in 2008. The last time that the United States went two years in a row with no hurricane landfalls was 2000-2001.
• Only three tropical storms have made landfall over the past two years. The last time that three or fewer tropical cyclones made landfall in any consecutive two-year period was 1990-1991.
“Fortunately, for the residents along the U.S. coastline, no hurricanes made landfall this year,” Gray said. “We were very lucky this year, given the heightened basinwide activity, to have very little storm activity near the U.S. coastline.”
The Atlantic has seen a very large increase in major hurricanes during the 16-year period of 1995-2010 (average 3.8 per year) in comparison with the prior 25-year period of 1970-1994 (average 1.5 per year). Klotzbach and Gray attribute this upturn in Atlantic major hurricanes to natural multi-decadal variability in the strength of the Atlantic thermohaline circulation and a concomitant increase in tropical Atlantic sea-surface temperatures.
These changes are not directly related to global sea-surface temperature increases or atmospheric CO2 concentrations, Gray has said.
The 2010 hurricane season had the following special characteristics:
• 88.25 named storm days occurred in 2010. This ties 2010 with 2008 for the sixth most-named storm days in a single season since 1944.
• Twelve hurricanes occurred in 2010. Since 1944, only two seasons, 1969 (12) and 2005 (15) have had the same or more hurricanes in a single season.
• Five major hurricanes formed during the 2010 hurricane season. Since 1944, only seven seasons (1950, 1955, 1961, 1964, 1996, 2004 and 2005) have had more than five major hurricanes form.
• No Category 5 hurricanes developed in 2010. This is the third consecutive year with no Category 5 hurricanes. The last time that two or more years occurred in a row with no Category 5 hurricanes was 1999-2002.
• Eleven named storms formed between Aug. 22 and Sept. 29. This is the most named storms to form during this period, breaking the old record of nine named storms set in 1933, 1949, 1984 and 2002.
• Five hurricanes formed during the month of October. Only 1870 (six hurricanes) and 1950 (five hurricanes) have had at least five systems reach hurricane strength for the first time during October.
• Igor and Julia both were at Category 4 status on Sept. 15. The only other time that two storms both were at Category 4 status in the Atlantic was on Sept. 15, 1926.
• Four Category 4 hurricanes (Danielle, Earl, Igor and Julia) formed in the Atlantic between Aug. 27 and Sept. 15 (20 days). This is the shortest time span on record for four Category 4 hurricanes to develop, breaking the old record of 24 days set in 1999.
The team will issue its first forecast for the 2011 hurricane season on Dec. 8, 2010.