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August 17, 2004
TRMM SEES RAIN FROM HURRICANES FALL AROUND THE WORLD
Since rain and freshwater flooding are the number one causes of death from hurricanes in the United States over the last 30 years, better
understanding of these storms is vital for insuring public safety. A recent study funded by NASA and the National Science Foundation offers insight
into patterns of rainfall from tropical storms and hurricanes around the world.
Researchers at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, Miami, and the National Oceanic and
Atmospheric Administration Atlantic Oceanographic and Meteorological Laboratory’s Hurricane Research Division, Miami, used data from
NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite to show how rain falls at different rates in different areas of a storm. The
results were published in the July issue of the journal Monthly Weather Review.
The results are already being used in a model developed at the Hurricane Research Division to estimate rainfall accumulation related to tropical
cyclones. The findings are important because they may help in the development of better forecasts.
The TRMM satellite offers the best measurements of how and where rain falls around tropical cyclones. This is because its orbit is low to the
Earth, allowing more detailed information on storms, and it was designed to cover the tropics.
Tropical cyclones consist of winds rotating around low- pressure centers in the tropics that can develop into everything from tropical storms to
Category 5 hurricanes.
From 1998 through 2000, TRMM observed 260 tropical cyclones in six major ocean basins. Researchers found that the rainfall intensity and where the
heaviest rains fell varied depending on a storm’s wind speeds, its location and the environment of each basin.
Scientists looked at three types of tropical cyclones, based on a standard system for classifying these storms. Tropical storms have wind speeds
of less than 73 miles per hour (mph). Category 1 and 2 hurricanes blow with winds of 74 to 110 mph, and Category 3 to 5 hurricanes’ winds range
above 110 mph.
“This study is important because we know very little about the rainfall distribution in tropical cyclones,” said lead author of the
study, Manuel Lonfat, a University of Miami researcher. “It revolutionizes our understanding of the distribution of rain in tropical
cyclones,” he added. Lonfat is a NASA Earth System Science Fellowship recipient.
“More than 50 percent of deaths in the U.S. from tropical cyclones over the last 30 years are related to freshwater flooding. So this is
currently a very large problem for the forecasting community,” Lonfat said.
When all storms were averaged together the most intense rainfall occurred within 50 kilometers (about 31 miles) of a storm’s center, with
evidence of very large rain rates as far as 300 to 400 kilometers (about 186 to 250 miles) from the center.
When all storms were averaged and analyzed basin by basin, storms in the North Indian basin were the wettest, and East- central Pacific storms
were the driest. The Atlantic and West Pacific storms showed similar rain rates: this at first surprised the researchers since Western Pacific storms
tend to be bigger and were presumed to be wetter.
Researchers also found that the storms were not symmetric, meaning that rain fell at different rates in different areas of a storm. If a round
storm were divided into four equal parts through the center, called quadrants, in general it was found that the heaviest rainfall occurred in one of
the front quadrants. However, the heaviest rainfall shifted from the front-left to the front-right quadrant as a tropical cyclone’s intensity
increased.
Tropical storms were less symmetric, while stronger hurricanes had a more symmetric inner core. In the Southern Hemisphere, the heaviest rain
occurred to the front-left of the storm’s path, while in the Northern Hemisphere the heaviest rainfall peaked in the front-right quadrant.
Normally, the only way to accurately measure rain falling from a hurricane is when it gets close enough to the coast to be picked up by National
Weather Service radars, or by rain gages. Since TRMM is space-based, researchers can assess the rainfall over vast tracts of ocean, where these
storms spend most of their lives.
For more information and images on the Internet, please visit:
http://www.gsfc.nasa.gov/topstory/2004/ 0817trmmhurricane.html
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Contacts:
Gretchen Cook-Anderson
Headquarters, Washington
Phone: 202/358-0836
Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, Md.
Phone: 607/273-2561
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Hurricane Charley, August 13 2004
TRMM observed Hurricane Charley as it crossed the Caribbean Sea and made landfall on the southwest coast of Florida on August 13. This image shows
the horizontal distribution of rain intensity and combines data from TRMM’s Precipitation Radar (PR), Microwave Imager (TMI) and Visible
Infrared Scanner (VIRS). Credit: NASA/NASDA
High-Resolution
Image
For more information about this image and Hurricane Charley, read the Natural Hazards Report about it.
Tropical Cyclones Observed by TRMM and Ocean Basins
This graphic shows locations of tropical cyclones observed by TRMM’s Microwave Imager instrument during the period from January 1, 1998 to
December 31, 2000. Each dot represents one TRMM observation. The solid lines indicate the boundaries of the six ocean basins analyzed in the study.
The six basins are: Atlantic (ATL), east-central Pacific (ECPAC), northwest Pacific (NWPAC), north Indian Ocean (NIND), south Indian Ocean (SIND),
and South Pacific (SPAC). Credit: Lonfat et al., University of Miami
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Towering Rain Structures in Hurricane Bonnie, 1998
In 1998, TRMM observed some of the largest chimney clouds seen from above inside Hurricane Bonnie, showing a (cumulonimbus) storm cloud, towering
like a skyscraper, 59,000 feet (18 kilometers) into the sky from the eyewall. Credit: NASA/NASDA
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Animation
Hurricane Floyd Rainfall
The map shows the surface rainfall for Hurricane Floyd on September 13, 1999. The rainfall was measured by TRMM’s Microwave Imager
instrument. The color coded rain rate is in inches per hour, with blues showing lighter rain and reds indicating higher rainfall. The distance
between each circular line growing from the storm’s center represents 10 kms. Credit: Naval Research Laboratory, reproduced in Lonfat et al.,
University of Miami
High-Resolution Image
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