Wednesday, June 29, 2011

Hurricane Season 2011: Tropical Storm Arlene (Atlantic Ocean/Caribbean Sea)

NASA Satellites See Strong Thunderstorms, Heavy Rain as Arlene Nears Landfall

Two different NASA satellites provided valuable information about the hundreds of thunderstorms that make up Tropical Storm Arlene as it nears landfall in northeastern Mexico. NASA's Aqua satellite measured cloud top temperatures giving clues about the strength of storms, while the TRMM satellite measured rainfall rates and cloud heights. All of this data is useful to forecasters in predicting Arlene's next moves.

The Tropical Rainfall Measuring Mission (TRMM) satellite had a good look at Arlene when it passed above on June 29, 2011 at 0502 UTC (0:02 AM CDT). At that time Arlene's winds were estimated to be about 34 knots (~39 mph) indicating that it was barely a tropical storm.

TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) data showed that Arlene was getting better organized and contained scattered heavy thunderstorms dropping rain at a rate of over 50 mm/hr (~2 inches). Some of the heaviest rainfall was not near the center of Arlene's circulation but was in feeder bands over land along the southwestern Gulf of Mexico. A 3-D analysis of Arlene's vertical structure using TRMM PR revealed that very powerful thunderstorms in a feeder band over the southeastern Yucatan Peninsula reached to heights of 17 km (~10.6 miles).

NASA's Aqua satellite passed over Tropical Storm Arlene on June 29, 2011 at 08:05 UTC (4:05 a.m. EDT). At that time, the Atmospheric Infrared Sounder (AIRS) instrument showed that most of Arlene's heaviest thunderstorms and coldest cloud top temperatures (-63F/-52C) were over the waters of the Gulf of Mexico. That data matched with the TRMM data that showed the heaviest rainfall was over open water.

At 1 p.m. EDT on June 29, Arlene's maximum sustained winds had increased to 50 mph (85 kmh). It was located just 95 miles (155 km) east of Tuxpan, Mexico and 150 miles east-southeast of Tampico. That put Arlene's center near 21.1 North and 95.9 West. It was moving west near 8 mph (13 kmh) and had a minimum central pressure of 1000 millibars. A hurricane watch is in effect for the coast of eastern Mexico from Barra De Nautla Northward to La Cruz and a tropical storm watch extends farther along the coast. For updates, visit: www.nhc.noaa.gov.

Residents in the area of the watches should prepare for gusty winds, heavy rainfall and rough surf.

Text credit: Rob Gutro, NASA's Goddard Space Flight Center, Greenbelt, Md.

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