Every hurricane season, clusters of showers and thunderstorms roll off the coast of Africa and head over the Atlantic toward America.

Most of these 60 or so tropical waves never do any harm, but about 10 eventually grow into tropical storms or monster hurricanes like Katrina or Andrew.

Researchers don't know exactly why some of these waves become menaces and others peter out.

So starting this week, NASA and the National Oceanic and Atmospheric Administration will try to find out by studying these tropical systems as they make their way west from their breeding ground in Africa.

Meteorologists know certain basics are needed for hurricanes to form: deep pools of warm water; warm, moist air; low air pressure. But all of those conditions can be in place, and still a storm won't start spinning.

"We need to better understand how it ramps up and why does it weaken," said Jason Dunion, a Hurricane Research Division scientist who will lead NOAA's efforts in the $4.5 million project.

While scientists have studied the area off Africa before, this will be the most in-depth research there, said Jeff Halverson, a NASA hurricane research scientist and a professor at the University of Maryland, Baltimore County.

The researchers hope their work will help forecasters make more accurate predictions of hurricane intensity.

While errors in forecasting storm tracks have been cut in half over the past decade or so, predicting how strong or weak a hurricane will become cannot be done with much accuracy.

Intensity predictions are about 15 to 20 years behind the progress in forecasting storm tracks, Dunion said.

Some data gathered by the teams will be fed in real time to computer models, so forecasters could see improvements in intensity forecasts this year, he said. Other information will be analyzed over the long term.

NASA is using a specially equipped plane based in the Cape Verde Islands 350 miles off Senegal to track and analyze the African easterly waves, which form over the eastern part of the continent and move west.

Forecasters believe more than 80 percent of hurricanes of Category 3 or higher come from these waves.

They will also examine the effects of the Saharan air layer, a large formation of hot, dry, dusty air that researchers say can stop hurricanes from developing.

NASA satellites, NOAA planes, weather radar and balloons will also be used during the monthlong project. From the air and space, the team will gather an unprecedented amount of data on temperature, humidity, air pressure, rainfall, dust particles and other factors.