April 7, 2009 –- Noted hurricane researchers Philip Klotzbach and William Gray at Colorado State University cut back their prediction Tuesday for the 2009 Atlantic hurricane season to a dozen named storms, forecasting an average year for tropical cyclones.
Hurricane season officially starts June 1 and runs through Nov. 30.
Klotzbach and Gray's early season prediction was for 14 named storms, but cooler sea surface temperatures, among other factors, prompted them to revise downward.
"We expect current weak La Nina conditions to transition to neutral and perhaps weak El Nino conditions by this year's hurricane season," Gray said in a press release. "If El Nino 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."
The team has seen unusual 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 an active Atlantic hurricane season.
The two predict that half of the 12 named storms will become hurricanes. Of those six, Gray and Klotzbach expect two to develop into major hurricanes of Category 3 or above with sustained winds of 111 mph or greater.
"We are calling for an average hurricane season this year — about as active as the average of the 1950 to 2000 seasons," Klotzbach said.
Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year. But this year's prediction bucks the trend of above-average storm activity in the years since 1995 — including 2005's record-breaking 28 storms.
These factors they see this year are similar to conditions that occurred during 1951, 1968, 1976, 1985, and 2001 seasons. These five seasons had about average activity, and Klotzbach and Gray predict the 2009 season will have activity in line with the average of these five years.
The team's forecasts are based on the premise that global oceanic and atmospheric conditions such as El Nino, sea surface temperatures and sea level pressures that preceded active or inactive hurricane seasons in the past provide meaningful information about similar trends in future seasons.
The team also predicted average major hurricane landfall risk in the Caribbean. It does not currently assign probability percentages to Caribbean islands, but will do so starting with its early June update — a new feature of their predictions.
Klotzbach and Gray do assign probabilities for mainland. "Based on our latest forecast, the probability of a major hurricane making landfall along the U.S. coastline is 54 percent compared with the last-century average of 52 percent," Klotzbach said.
The long-term average is 52 percent.
The team gave a 1 in 3 chance that a major hurricane will make landfall on the U.S. East Coast, including the Florida peninsula, in line with the long-term average.
The probability that a major hurricane will make landfall on the Gulf Coast from the Florida panhandle west to Brownsville, Texas, is also about 1 in 3. The long-term average is 30 percent.
The team will issue forecast updates on June 2, Aug. 4, Sept. 2 and Oct. 1. The August, September and October forecasts will include separate forecasts of August-only, September-only and October-only Atlantic basin tropical cyclone activity.
V.I. Territorial Emergency Management Agency Director Mark Walters said he doesn't put much stock in Klotzbach and Gray's predictions, noting that it only takes one storm to hit for a disaster to occur.
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