In its 28th year of issuing predictions, the Colorado State University forecast team today predicted an above-average 2011 Atlantic basin hurricane season. The team slightly reduced its early December prediction, but still called for an active season based on current La Nina conditions that are expected to transition to near-neutral conditions during the heart of the hurricane season.
The CSU team now calls for 16 named storms instead of 17 forming in the Atlantic basin between June 1 and Nov. 30. Nine of those are expected to turn into hurricanes with five developing into major hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.
“We expect that anomalously warm tropical Atlantic sea surface temperatures combined with neutral tropical Pacific sea surface temperatures will contribute to an active season,” said Phil Klotzbach of the CSU Tropical Meteorology Project. “We have reduced our forecast slightly from early December due to a combination of recent ocean warming in the eastern and central tropical Pacific and recent cooling in the tropical Atlantic.”
“It is recommended that all vulnerable coastal residents make the same hurricane preparations every year, regardless of how active or inactive the seasonal forecast is,” Klotzbach said. “It takes only one landfall event near you to make this an active season.”
The hurricane forecast team made this early April forecast based on a new forecast scheme that relies on 29 years of historical data. The hurricane team's forecasts are based on the premise that global oceanic and atmospheric conditions - such as El Nino, sea surface temperatures, sea level pressures, etc. - that preceded active or inactive hurricane seasons in the past provide meaningful information about similar conditions that will likely occur in the current year. The team’s annual predictions are intended to provide a best estimate of activity to be experienced during the upcoming season, not an exact measure.
“We remain - since 1995 - in a favorable multi-decadal period for enhanced Atlantic Basin hurricane activity, which is expected to continue for the next 10-15 years or so,” said Gray. “Except for the very destructive hurricane seasons of 2004-2005, United States coastal residents have experienced no other major landfalling hurricanes since 1999. This recent 9 of 11-year period without any major landfall events should not be expected to continue.”
Five years since 1949 exhibited February-March characteristics most similar to the oceanic and atmospheric features observed during February-March 2011: 1955, 1996, 1999, 2006 and 2008. All years but 2006 had either neutral or La Nina conditions during the hurricane season, and all years but 2006 were very active hurricane seasons.
The team predicts that tropical cyclone activity in 2011 will be approximately 175 percent of the average season. By comparison, 2010 witnessed tropical cyclone activity that was 196 percent of the average season.
The hurricane forecast team's probabilities for a major hurricane making landfall on U.S. soil:
- A 72 percent chance that at least one major hurricane will make landfall on the U.S. coastline in 2011 (the long-term average probability is 52 percent).
- A 48 percent chance that a major hurricane will make landfall on the U.S. East Coast, including the Florida Peninsula (the long-term average is 31 percent).
- A 47 percent chance that a major hurricane will make landfall on the Gulf Coast from the Florida Panhandle west to Brownsville (the long-term average is 30 percent).
The team also predicts a 61 percent chance of a major hurricane tracking into the Caribbean (the long-term average is 42 percent).
Probabilities of tropical storm-force, hurricane-force and major hurricane-force winds occurring at specific locations along the U.S. East and Gulf Coasts are listed on the forecast team's Landfall Probability website at http://www.e-transit.org/hurricane. The site provides U.S. landfall probabilities for 11 regions and 205 individual counties along the U.S. coastline from Brownsville, Texas, to Eastport, Maine. Landfall probabilities for regions and counties are adjusted based on the current climate and its projected effects on the upcoming hurricane season. Probabilities are also available for the Caribbean and Central America. Klotzbach and Gray update the site regularly with assistance from the GeoGraphics Laboratory at Bridgewater State University in Massachusetts.
The team will issue forecast updates on June 1 and Aug. 3.