As the 2007 Atlantic hurricane season gets officially under way today, residents of the United States, Mexico, and the Caribbean are bracing for what weather experts are saying will be another storm-filled six months.

Seventeen tropical storms will form in the Atlantic Basin, which includes the Caribbean Sea and Gulf of Mexico, between June 1 and November 30, according to Colorado State University (CSU) forecasters William Gray and Phil Klotzbach.

Nine of those storms will strengthen into hurricanes with winds of at least 74 miles (120 kilometers) an hour, the experts say.

The "very active" season will also see as many as five major hurricanes - storms with sustained winds of at least 111 miles (179 kilometers) an hour - the CSU forecasters predict.

One of those major hurricanes will probably make landfall somewhere on the Gulf of Mexico or Atlantic coasts, the scientists say.

Gray and Klotzbach's prediction follows other forecasts that also call for a busy season.

The National Oceanic and Atmospheric Administration predicts 13 to 17 named storms. The NOAA forecasters say that seven to ten of those storms will become hurricanes, and three to five will become major hurricanes.

And a forecast team at North Carolina State University (NCSU) headed by Lian Xie predicts 12 to 14 named storms, eight or nine hurricanes, and four or five major hurricanes. The NCSU forecast team foresees one or two hurricanes making landfall in the U.S.

During an average hurricane season, about ten tropical storms form, spawning six hurricanes and two major hurricanes.

Continuing Trend?

If this summer does produce a high number of hurricanes, it will continue a trend of more active seasons that began in 1995.

Hurricane activity in the Atlantic is regulated by cyclical ocean currents that increase and decrease water salinity, said Gray, a pioneer in long-range hurricane forecasting.

When salinity is higher, as it is now, the water is warmer and more storms 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.

"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.

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."