When salinity is higher, as it is now, the water is warmer and more storms form.
(See an interactive feature on how hurricanes form.)
But forecasters don't think the early formation of Tropical Storm Andrea three weeks ago off the Georgia coast offers any indications for the season ahead.
"May, June, and July don't usually say much about the overall season," Klotzbach, of CSU, said. "If you see early activity in the Caribbean or tropical Atlantic, however, that means it's going to be a very active season."
The 2007 forecast is nearly identical to last summer's pre-season predictions. But coastal residents got an unexpected breather last year when the formation of a Pacific weather phenomenon known as El Niño helped put a damper on Atlantic hurricanes.
Only nine tropical storms formed in 2006, with just five becoming hurricanes. And the season saw two major hurricanes, compared to the five that were forecast.
The El Niño has vanished, however, and forecasters say another Pacific phenomenon called La Niña could form in its place. If this happens, conditions in the Atlantic could become more favorable for hurricane formation.
Dependable Forecast?
That quieter-than-expected 2006 Atlantic season has raised some public skepticism about the validity of hurricane forecasts. (Related: "Mild U.S. Hurricane Season Defied Predictions" [November 30, 2006].)
"For the most part, the criticism of seasonal outlooks is merited," said Stu Ostro, a meteorologist with the Weather Channel, an Atlanta-based commercial forecasting service.
NCSU's Xie—whose 2006 forecast was closer to reality than other predictions—said long-range hurricane forecasting is "not a 100-percent business."
"It's not that it'll be wrong all the time or right all the time," Xie said. "That's the nature of long-range predictions."
Meteorologists make their forecasts by plugging weather data such as sea-surface temperatures and upper-level winds into computer models. But even though the computer models are similar or identical, meteorologists often differ on the data they consider most important, Xie said.
If one forecaster puts more emphasis on upper-level winds than another forecaster, the computer predictions will probably turn out different.
Despite last year's inaccurate prediction, Xie thinks Gray's forecasts are generally accurate.
"If you look at his past record overall, he was actually the best in the country," Xie said. "He sets the benchmark for others to beat, and so far, no one has beaten him."
Global Warming Debate
An active 2007 season could re-stoke the debate among scientists about whether global warming is causing more hurricanes to form. (Related: "Warming Was Top Factor in 2005 Hurricanes, New Data Says" [June 26, 2006].)
The debate became especially contentious during the 2005 season, which saw a record 27 named storms—including the devastating Hurricane Katrina.
Meteorologists such as Kerry Emanuel at the Massachusetts Institute of Technology say that greenhouse gases are causing a warming trend and that this trend is a major factor in recent active seasons.
Not all scientists agree, however.
The Weather Channel's Ostro says the debate about global warming and hurricanes "is a legitimate one."
"The bottom line is we don't know exactly how hurricanes have been affected or will be in the future," Ostro said. "So far, much of the research has focused on such things as [global warming's possible effect] on wind shear in the tropics and sea surface temperatures."
Xie, of NCSU, also says the jury is still out on global warming and hurricanes.
"By looking at all the data for the past 20 or 30 years, if there's been any effect by global warming, I would say it's small," Xie said. "I'm not yet convinced that global warming has affected hurricanes."
But that might change eventually, Xie added.
"If global warming is occurring at the pace projected by scientists," he said, "then that global warming likely will lead to stronger hurricanes in the future, but not by much."
Willie Drye is the author of Storm of the Century: The Labor Day Hurricane of 1935, published by National Geographic.
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