Nearly every year, hurricane specialists at the National Hurricane Center find a new toy in their forecasting tool boxes: High flying jets to pierce the storm. A better computer program. A new analytical technique. Each improvement means forecasts become marginally better, typically on the order of a few percentage points.
But when next hurricane season rolls around, a new and unusual breed of satellite data could allow an unprecedented jump in forecast accuracy, according to a report being presented Tuesday at the annual meeting of the American Meteorological Society's meeting in Long Beach, California.
The Tropical Rainfall Measuring Mission (TRMM) satellite, a joint project between NASA and the Japanese government, profiles horizontal slices of a storm in the tropics to get a picture of how rain changes with altitude. The information is critical in forecasting how a tropical storm or hurricane might develop.
Examining latent heat
When water vapor condenses into raindrops, heat is released. Researchers call it latent heat, and it is a key factor in cloud formation and storm development.
TRMM, launched in 1997 and now eyeballing a relatively narrow swath of the tropics where hurricanes develop, is the first tool to provide such data. Tropical rainfall, which falls between 35 degrees north latitude and 35 degrees south latitude, comprises more than two-thirds of the rainfall on Earth.
Researchers at Florida State University say that by adding the TRMM rainfall observations to information collected by other meteorological satellites, they can more than triple the accuracy of rainfall forecasts over the coming 12-hour period.
The new method does not scuttle previously used computer models, but instead builds on them.
Researchers examined the behavior of a number of different forecast models and selected those properties from each model that lead to the true rainfall as observed by the TRMM satellite during past storms. These model properties are then used to predict the rainfall for three days into the future with remarkable success.
"Including rainfall into the multi-forecast model, or super-ensemble model is a unique approach," said T.N. Krishnamurti, the paper's lead author and a TRMM scientist at Florida State University. "Our research has shown that the global, as well as the regional skills, using the multi-analysis super-ensemble, are higher with TRMM research data."
The forecast results are based on five experiments in August 1998. Experimental forecasts made using the new technique during 1999 correctly forecast the track of major hurricanes such as Dennis and Floyd, researchers said.
The findings will appear in an upcoming edition of the Journal of Climate.
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