Subtropical Storm Andrea formed off the southeastern U.S. coast Wednesday, more than three weeks before the official start of hurricane season, according to forecasters.

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MAPS: See Storm Track -- Landfall

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The National Hurricane Center said the year's first named storm has top sustained winds near 45 mph. It's centered about 140 miles southeast of Savannah, Georgia.

A hurricane hunter plane examined the swirling low-pressure system in the Atlantic Ocean that continued to show signs that it could form into a tropical storm early Wednesday.

"The plane is criss-crossing through the heart of the storm to see if it is taking on the tropical characteristics," Local 6 meteorologist Larry Mowry said.

The system was located about 150 miles east of Jacksonville, Mowry said.

Forecasters said Andrea has the warm center characteristic of tropical storms but its core is not particularly well defined.

Eighteen tropical storms and four hurricanes have been recorded in May since 1851. The earliest hurricane to strike the U.S. was Alma in northwest Florida on June 9, 1966.

Private and university forecasters have predicted that the 2007 season that starts June 1 and ends Nov. 30 will be especially active, producing up to 17 tropical storms and hurricanes and a “well above average” possibility of at least one striking the U.S. The federal government plans to release its predictions May 22.

The Atlantic basin has been in a busy period for hurricanes since 1995. Some federal forecasters believe this is part of a natural cycle. But the Intergovernmental Panel on Climate Change, a U.N.-sponsored group, says global warming caused by humans has led to an increase in stronger hurricanes. Rain will move into parts of Central Florida Wednesday, especially in Flagler and Volusia counties.

Most of the rain associated with the low is on the south and east side of the storm.

"This system, because it is just staying off our coastline, is really doing a number along our beaches," Mowry said.

Smoke Blankets Central Florida

Heavy winds have pushed smoke from several Florida brush fires over Orlando and parts of Central Florida.

"The smoke is very thick in many spots," Mowry said. "Visibility is down to around a mile in Seminole County. And even in parts of Orange County, we are seeing visibility very low."

Residents with breathing problems or asthma are urged to take precautions if there are smoky conditions around their homes.

Watch Local 6 News for more on this story.