The Colorado State University (CSU) forecast team predicts an average 2009 Atlantic basin hurricane season based on the potential for a weak El Niño event and an observed cooling of tropical Atlantic sea-surface temperatures.
The team anticipates 12 named storms forming in the Atlantic basin between June 1 and Nov. 30. Six are predicted to become hurricanes; of those six, two are expected to develop into intense or major hurricanes with sustained winds of 111 mph or greater.
"We expect current weak La Niña conditions to transition to neutral and perhaps weak El Niño conditions by this year's hurricane season. If El Niño conditions develop for this year's hurricane season, it would tend to increase levels of vertical wind shear and decrease levels of Atlantic hurricane activity," says William Gray, who is beginning his 26th year forecasting hurricanes at CSU.
The team has seen anomalous cooling of sea-surface temps in the tropical Atlantic over the past few months. Cooler waters are associated with dynamic and thermodynamic factors that are less conducive for an active Atlantic hurricane season.
"Based on our latest forecast, the probability of a major hurricane making landfall along the U.S. coastline is 54% compared with the last-century average of 52%," says lead forecaster Phil Klotzbach of the CSU hurricane team. "We’re calling for an average hurricane season this year – about as active as the average of the 1950-2000 seasons."
In addition to its overall prediction that there’s a 54% chance of a hurricane making landfall in the U.S., they predict a 32% chance that a major hurricane will make landfall on the U.S. East Coast, including the Florida Peninsula (the long-term average is 31%), and a 31% chance that a major hurricane will make landfall on the Gulf Coast from the Florida Panhandle west to Brownsville, TX (the long-term average is 30%).
Probabilities of tropical storm-force, hurricane-force and intense 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, TX, to Eastport, ME. The website is the first publicly accessible Internet tool that adjusts landfall probabilities for regions and counties based on the current climate and its projected effects on the upcoming hurricane season. Additional info is also available online.