With El Nino no longer running interference, we can expect more hurricanes and tropical storms this summer, forecasters say.
Scientists at Colorado State University say the dissipation of the El Nino weather pattern in the Pacific in recent months is likely to bring more hurricanes sweeping up the Atlantic coast beginning in June.
Whether the culprit is global climate change or cyclical patterns, this year's hurricane season is likely to be a bad one, the forecasters say.
"We are predicting a very active season this year," said Philip J. Klotzbach, a research associate in the Department of Atmospheric Science at Colorado State University.
The Colorado State report is the first of three traditional hurricane forecasts issued for a season that begins June 1 and ends Nov. 30.
The forecasters don't always agree.
AccuWeather.com is due to issue a forecast in early May, followed by the National Weather Service's National Hurricane Center on May 22.
Klotzbach and forecaster William M. Gray are predicting 17 named storms, including nine hurricanes, five of which will be Category 3 storms with winds of at least 111 mph.
Still, the report says the East Coast is not likely to be hit as hard as it was in 2005 or 2004, when a series of hurricanes, including Katrina, battered Florida and the Gulf Coast.
But the number of storms predicted is almost twice the long-term average - for the record, that's 9.6 named storms, 5.9 of which are hurricanes, including 2.3 major hurricanes.
For a storm to merit an official name, it must have sustained winds of 39 mph. It attains hurricane status at 74 mph.
Hard to pin down
Forecasters concede that this is an inexact science.
Last April, the Colorado group predicted nine hurricanes for 2006, but the season brought only five - none of which made landfall in the U.S.
This year, forecasters say, there is a 74 percent chance that at least one Category 3 hurricane will strike the U.S.
"We're not going to be as fortunate as we were last year," Klotzbach said.
Kenneth W. Reeves, director of forecasting operations at AccuWeather.com, agreed that this year's hurricane season won't be as busy as 2004 and 2005, but it should be an active one, he said.
"We do think it'll be above normal, with the hardest-hit areas Florida and the Gulf Coast," Reeves said.
Forecasters base hurricane predictions on a variety of factors known to precede active or mild seasons, including sea surface temperatures in the Atlantic and El Nino weather patterns.
El Nino is a periodic warming of surface waters in the eastern and central tropical Pacific that affect global weather patterns.
"We're all basically looking at the same data. It's just a case where we will continue to monitor the situation for a little longer before making our predictions," said Dennis Feltgen, a meteorologist and spokesman for the National Weather Service's National Hurricane Center.
Klotzbach said two factors point to a strong hurricane season. First, sea surface temperatures are about one-half to 1 degree Fahrenheit higher than normal in the Atlantic Ocean.
"Where the warmest water is, those are the best conditions for hurricanes," Klotzbach said.
Second, El Nino weather patterns brewed in the tropical Pacific are known to curb hurricane intensity by creating atmospheric conditions that promote wind shear in the Atlantic.
Wind shear tears into hurricanes as they form and stunts their growth, he said.
"El Nino has dissipated quite a bit in February and March," Klotzbach said, and forecasters expect neutral or unusually cool conditions to replace it.
The weakening of El Nino prompted Klotzbach and Gray to increase the hurricane estimate from their initial forecast, issued in December.
At that time, they predicted 14 named storms, seven of them hurricanes - three of which are expected to be intense.
Unlike some climate scientists, Klotzbach and Gray attribute increased hurricane activity to cyclical weather patterns and argue that it can't be blamed specifically on global warming.
The Atlantic basin is in the midst of an active cycle of hurricane activity that began in 1995 and is expected to continue for another 10 years or so, Klotzbach said.
These 20- to 25-year cycles of activity are followed by relatively quiet stretches, with a history that can be traced back to the 1940s, he said.
"We think the current active season has about 10 to 15 more years to go," Klotzbach said.