Posted on 05 Jun 2009
The Colorado State University hurricane forecast team predicted June 2 a slightly below-average 2009 Atlantic-basin hurricane season based on a cooler-than-normal tropical Atlantic and the greater potential for a weak El Nino during the bulk of the season.
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 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.
"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."
The team has seen anomalous cooling of sea surface temperatures in the tropical Atlantic 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 include:
* 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, Texas (the long-term average is 30 percent).
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.
Gray and Klotzbach advise coastal residents not to change their hurricane preparedness measures because of a less active seasonal forecast because major hurricanes can devastate coastal communities in less active seasons.