Colorado State University’s hurricane team announced it has slightly lowered its 2009 Atlantic hurricane forecast based on developing El Nino conditions that are expected to intensify during the remainder of the hurricane season.
“We have witnessed the development of an El Nino event over the past couple of months,” said team member William Gray. “These conditions are expected to intensify to a moderate El Nino over the next few months. El Nino events tend to be associated with increased levels of vertical wind shear and decreased levels of Atlantic hurricane activity.”
The revised prediction calls for 10 named storms forming in the Atlantic basin between June 1 and Nov. 30. Four of the 10 storms are predicted to become hurricanes, and of those four, two are expected to develop into major hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.
The university’s scientists reduced their forecast from June's prediction of 11 named storms, five hurricanes and two major hurricanes. Long-term averages are 9.6 named storms, 5.9 hurricanes, and 2.3 major hurricanes per year.
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 46% compared with the last-century average of 52%, the scientists report.
The hurricane forecast team's probabilities for a major hurricane making landfall on various portions of the U.S. coast:
• A 27% chance that a major hurricane will make landfall on the East Coast, including the Florida peninsula (the long-term average is 31%)
• A 26% 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%)
• New with this year’s forecasts are probabilities that a major hurricane will make landfall in the Caribbean and Central America. The team lowered that probability to 37% (the long-term average is 42%).
Additionally, the team predicts tropical cyclone activity in 2009 will be 85% of the average season. By comparison, 2008 witnessed tropical cyclone activity that was about 160% of the average season.
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