Colorado State University researchers raised their expectations for this year’s Atlantic hurricane season to 13 named storms, just above average.
Five of those storms may become hurricanes and two may develop into major systems, said the team, which pioneered long- range hurricane forecasting 29 years ago. Its April prediction for 10 storms, four of them hurricanes and two of them major, was increased because an El Nino pattern that would limit Atlantic storms hasn’t shown signs of forming yet.
“We have had a lot of uncertainty this season, it is a really, really tough call,” Phil Klotzbach, lead author of the study, said by telephone. “I know it sounds like a cop-out but that’s kind of where we’re at. The real challenge with this year is that we are really uncertain about El Nino.”
The season, which officially began today and runs through Nov. 30, is closely watched because the storms are a threat to oil and natural gas interests in the Gulf of Mexico and agriculture in the U.S. South. The Gulf accounts for 29 percent of U.S. oil output and 40 percent of refining capacity, while Florida is the second-largest citrus producer behind Brazil.
Klotzbach said the two storms the Atlantic has already produced in 2012, Alberto and Beryl, aren’t an indication of how active the rest of the season will be.
“It is certainly not a done deal,” Klotzbach said. “If we didn’t get one, I wouldn’t say I would be shocked. The next few weeks are going to be critical to push it one way or the other.”
Water temperatures in the Pacific can influence Atlantic wind shear, when winds at upper and lower levels in the atmosphere move at different speeds or directions. Tropical systems can have their tops torn off or tipped to one side by shear, robbing them of strength and organization.
If El Nino doesn’t form, the number of storms may be higher, Klotzbach said.
The Atlantic itself is cooler than last year, which may limit the number of storms because tropical systems build on warm ocean water. The most active part of the six-month season is from about Aug. 20 to Oct. 20.
According to the Colorado State report, some years with pre-season storms have gone on to be active, while others haven’t. Klotzbach said the two storms that formed so far were close to the U.S. and grew out of weather fronts. Neither formed deep in the Atlantic the way storms will later in the season, he said.
“Early storm activity doesn’t give you much of a signal,” Klotzbach said.
A storm gets a name when its top sustained winds reach 39 miles (63 kilometers) per hour. It becomes a hurricane with 74- mph winds and a major system, Category 3 or higher on the Saffir-Simpson scale, when its sustained winds grow to 111 mph.
The 30-year average in the Atlantic is for 12 named storms, six of them hurricanes and three of them major systems, according to the National Hurricane Center in Miami.
Last week, the National Oceanic and Atmospheric Administration predicted nine to 15 named storms would form, with four to eight growing into hurricanes and as many as three becoming major systems.
Colorado State last year predicted 16 storms, with nine becoming hurricanes. In 2011, like 2010, 19 storms formed in the Atlantic, which tied for the third-most active season in records going back to 1851. The mark for most storms in a single six- month season is 28 in 2005.
To contact the reporter on this story: Brian K. Sullivan in Boston at Bsullivan10@bloomberg.net
To contact the editor responsible for this story: Dan Stets at firstname.lastname@example.org