MIAMI – A fleet of special balloons may soon help hurricane forecasters better predict the path of storms. But at a cost of up to $2,000 a pop, these aren’t your average birthday party decorations.

The clear, pyramid-shaped balloons test-launched Friday in Miami by researchers and students are several feet tall and carry a palm-sized package of electronics and a transmitter that’s a little bit longer than a pencil. Researchers hope that by next hurricane season, hundreds of balloons could be launched as a research flotilla sending back data when a storm threatens in the Atlantic.

Currently, scientists have a limited amount of data about atmospheric conditions over the ocean. With hundreds of balloons launched from the southeastern coast of the United States and Caribbean islands, they could fill a data gap, scientists say. With a few years testing, researchers hope the data could dramatically improve the three-, four- and five-day predictions of the path of a storm, meaning better predictions of where storms will hit and reducing the miles of coastline that must be evacuated.

Tim Lachenmeier, who helped design the balloons for the National Oceanic and Atmospheric Administration, was teaching University of Miami students how to launch them Friday. He said balloons are becoming popular again as scientific tools.

“People like to say balloons are not rocket science, but we support a lot of rocket science,” he said.

The idea isn’t to send the balloons directly into storms but to have them probe the winds hundreds of miles around them: winds that steer a hurricane and determine its course.

Equipped with a GPS unit, the balloons would be launched from various locations after a storm appears in the Atlantic Ocean and then staggered over a period of days so data would come back continuously. The balloons would stay aloft from two to seven or more days, sending back their altitude and position every 15 minutes, before losing their helium and crashing into the ocean.

Currently, researchers get information about steering currents several ways. Over land, National Weather Service offices launch weather balloons twice a day. Unlike the hurricane balloons, which will float for days, the weather service balloons send back data for between an hour and a half and two hours before they pop and fall back to land.

Over the ocean, data is sparser. NOAA sends planes to gather some, which forecasters call invaluable. Satellites send back information, but they only pass over a given area once or twice a day. Balloons would add to the available information.

The balloons won’t improve the forecasts right away, however. It will likely take several years before data from the balloons are formally part of forecast models, said Justyna Nicinska, project manager for the balloons.

The first time NOAA flew an aircraft around a storm in the late 1990s to gather data, for example, it made forecast models worse, “much worse,” said former National Hurricane Center director, Max Mayfield. That was because the data wasn’t evenly sampled around the storm, Mayfield said.

“You want to make sure you’re making a positive impact,” Mayfield said.

The balloon project now has about $1.5 million in funding from the Department of Homeland Security and NOAA. Scientists have 130 of the mylar balloons available for this season’s pilot project, which will begin in October. In the first use, smaller 3-foot tall balloons will fly at 12,000 feet and larger 5-foot balloons will fly at 26,000 feet, about 3,000 feet below the height of Mount Everest.

Researchers have just over two months before the 2008 Atlantic hurricane season ends Nov. 30, but are already planning ahead, hoping to bring the cost of the balloons down to a few hundred dollars but also hoping to add additional sensors that could send back other data like temperature, pressure and relative humidity.

On Friday, University of Miami graduate students Yumin Moon and Chiaying Lee, both 26 and getting Ph.D.s in meteorology, filled their first balloon in a conference room, a tank of helium hissing as they checked the balloon was inflating properly. Lee said she’d only filled up party balloons before, and “they don’t count,” she said.