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Research / Discovery

Hurricane forecast team lowers forecast

June 3, 2009

The Colorado State University hurricane forecast team has predicted a slightly below-average 2009 Atlantic basin season based on a cooler-than-normal tropical Atlantic and the greater potential for a weak El Nino during the bulk of the hurricane season.

2 major hurricanes expected

The team now anticipates 11 named storms forming in the Atlantic basin between June 1 and Nov. 30. Five of the storms are predicted to become hurricanes, and of those five, two are expected to develop into major hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.

The scientists reduced their forecast from April's prediction of 12 named storms, six hurricanes and two major hurricanes. Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes per year.

Photo at right:  Phil Klotzbach (left) and William Gray (right)

"We believe that there is a slightly greater chance of a weak El Nino developing this summer/fall than there was in early April," said William Gray, who is beginning his 26th year forecasting hurricanes at Colorado State University. "El Nino conditions would likely increase levels of vertical wind shear and decrease Atlantic hurricane activity."

Cooling of sea surface temps

The team has seen anomalous cooling of sea surface temperatures in the tropical Atlantic over the past few months. Cooler waters are associated with dynamic and thermodynamic factors that are less conducive for hurricane formation.

The team also updated its U.S. landfall probabilities. These probabilities are calculated based upon 20th century landfall statistics and then adjusted by the latest seasonal forecast.

"The probability of a major hurricane making landfall along the U.S. coastline is 48 percent compared with the last-century average of 52 percent," said lead forecaster Phil Klotzbach. The hurricane forecast team's probabilities for a major hurricane making landfall on various portions of the U.S. coast:

- A 28 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 28 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).

Caribbean and Central America landfall probabilities

New with this forecast are landfall probabilities for the Caribbean and Central America. This season, the forecast team expects a 39 percent chance of a major hurricane tracking into the Caribbean, which is slightly lower than the long-term average of 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 within a variety of time periods are listed on the forecast team's Landfall Probability website. 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.

Klotzbach and Gray update the site regularly with assistance from the GeoGraphics Laboratory at Bridgewater State College in Massachusetts. In addition, probabilities for various islands in the Caribbean and landmasses in Central America are now available on the Landfall Probability website.

The team will issue a final seasonal forecast update on Tuesday, Aug. 4.

Full news release

Contact: Emily Wilmsen
Phone: (970) 491-2336