Rainbands Offer Better Forecasts Of Hurricane Intensity

Atmospheric scientists from the University of Miami RosenstielSchool of Marine & Atmospheric Science (RSMAS), the University ofWashington and the National Center for Atmospheric Research (NCAR) inBoulder, Colo., will participate in the new project, called theHurricane Rainband and Intensity Change Experiment, or RAINEX.

RAINEX will study how the outer rain bands and inner eye of a hurricane interact to influence a storm's intensity.

"While great progress has been made in forecasting hurricane tracks,we need to improve forecasting of hurricane intensity," said SteveNelson, director of the National Science Foundation's (NSF) physicaland dynamic meteorology program, which funds RAINEX. "Many factorsaffect the intensity of hurricanes," Nelson said. RAINEX scientistswill investigate one of those factors: the interactions betweenhurricane rainbands and the eyewall. "From RAINEX, we will betterunderstand the impact of rainbands on a hurricane's maximum winds," hesaid.

While researchers have studied the eye and outer rainbands ofhurricanes extensively, "few, if any, experiments have ever examinedthese two components together and how their interaction might affect astorm's strength," said Shuyi Chen, a meteorologist and physicaloceanographer at RSMAS and a RAINEX principal investigator. "The outerbands of a hurricane often have strong winds and lots of rain, and thatcan actually affect the overall intensity of a hurricane," she said.

RAINEX will study this interaction using data recorded fromhurricane research flights. Starting on Aug. 15 and continuing throughthe remainder of this year's Atlantic hurricane season, two NOAA P3aircraft, along with a U.S. Navy P3 aircraft, all equipped with Dopplerradar, will fly simultaneously into hurricanes well before theythreaten landfall.

The University of Washington and NCAR, will conduct research usingairborne Doppler radar analysis. RSMAS will construct astate-of-the-art hurricane model using the data collected from theresearch flights.

"These flights can be turbulent, especially when we're penetrating ahurricane's rainbands," said NCAR scientist Wen-Chau Lee. "I thinkthat's the wild card, the challenge of the experiment: to captureinternal rainband structure and its interactions with the eye wall inthose conditions."

"We hope to find an explanation for why a hurricane changes inintensity, from the relationship between the inner and outer parts ofthe storm," said Robert Houze, an atmospheric scientist at theUniversity of Washington and a RAINEX co-principal investigator. "Thesestorms can jump up in intensity, or drop a full category in a day, abig challenge."

Flying in the hurricane's outer bands and into the eye wall,scientists aboard the aircraft will use sophisticated Doppler radar andGPS dropsondes to record wind speed and direction, temperature,humidity, atmospheric pressure and other critical data.

Much of what scientists currently know about the interaction betweenthe outer rainbands and the eye wall of a hurricane comes from thestate-of-the-art numerical models developed for hurricane research andprediction, which can provide very detailed information but may not becompletely accurate.

Researchers need solid data to validate these models, they say. "Weneed to know whether or not our models are accurate, and the data wecollect from RAINEX will give us the information we need," Chen said.

Once the data are collected, the researchers will all analyze andshare this information with hurricane operational centers and nationalenvironmental prediction centers throughout the country, and the world.