As Hurricane Earl barrels toward the eastern seaboard of the United States, coastal residents don't know if they should evacuate in case the storm makes landfall. They rely on forecasters analyzing computer models, but those predictions differ. A new hurricane-monitoring mission that's now underway hopes to reduce this uncertainty by gathering atmospheric and environmental storm data never before obtained.

NASA, the National Oceanic and Atmospheric Administration (NOAA), and the National Science Foundation (NSF) are conducting the largest tropical storm and hurricane monitoring mission to date. The mission involves simultaneously flying up to seven aircraft, each equipped with sophisticated instrumentation, to gather data from the time of a storm's inception to its dissipation.

"There is a lot about storms that we don't know--why does a storm rapidly intensify? How do things like aerosols, atmospheric moisture, and ocean currents affect a storm's development?" says Gerry Heymsfield, a NASA mission scientist. "The new measurements we are making will significantly enhance our understanding and ultimately improve forecast models."

The collaborative hurricane monitoring project includes three different missions: NASA's Genesis and Rapid Intensification Processes experiment, which will focus on how tropical storms form and develop into hurricanes; NOAA's Intensity Forecasting Experiment, designed to better understand and predict intensity changes in storms like Hurricane Earl; and NSF's Pre-Depression Investigation of Cloud Systems in the Tropics project, which will look at the beginning stages of a storm. The missions began in late August and will continue to the end of September. Hurricane Earl, says Heymsfield, will be one of the first storms to produce enough data to yield compelling results.

On Monday, NASA's DC-8 aircraft and NOAA's two jet planes flew through Hurricane Earl as it passed through the Caribbean. Although most of the information gathered will take years to analyze, the aircraft do obtain some real-time data using dropsondes, which are balloons dropped into the storm. The dropsondes measure the storm's temperature, humidity, and pressure. The information provides a profile of the hurricane that can be assimilated into mathematical models for forecasting its track and intensity. Other instrumentation on the planes measure such things as precipitation rate, cloud distribution, winds, water content, and particle profiles.