Hurricane Season 2011: Tropical Storm 5A (Northern Indian Ocean)

Tropical Storm 5A More 'Well-Rounded' on NASA Infrared Imagery, for Now

Over the past several days Tropical Storm 05A has become better organized on infrared satellite imagery from NASA. Imagery from NASA's Aqua satellite over two days has shown that the cold cloud tops in the cyclone have become more rounded as the storm consolidates and strengthens.

NASA's Aqua satellite made two passes over Tropical Storm 05A (5A) and noticed the changes. The first pass happened on Nov. 26 at 08:23 UTC (3:23 a.m. EST and the infrared image from the Atmospheric Infrared Sounder (AIRS) instrument on Aqua revealed that 5A's clouds were not circular in nature, indicating a struggle within the storm to get organized. At that time, 5A was located near 9.3 North and 73.6 East, about 160 miles (257 km) west-southwest of Cochin, India.

By Nov. 27 at 21:23 UTC (4:23 p.m. EST) 5A had become circular in shape indicating that the storm did get better organized. At that time, maximum sustained winds were near 40 mph (35 knots/65 kmh) and it was 360 miles (579 km) south-southwest of Mumbai, India. That organization may be short-lived however, as wind shear increases and batters the circulation of the storm.

AIRS infrared imagery measures cloud top and sea surface temperatures, two factors that help determine the behavior of tropical cyclones. The colder the cloud tops are the higher the clouds and the stronger the thunderstorm (and heavier rain). The warmer the sea surface temperatures are, the higher the thunderstorm cloud tops are likely to rise and the stronger they are likely to become. Sea surface temperatures of at least 80F (26.6C) are needed to maintain a tropical cyclone, and they are currently near 84.2F (29C) in the Bay of Bengal where 5A lingers.

On Nov. 28 at 1500 UTC (10 a.m. EST), Tropical Storm 05A had maximum sustained winds still holding near 40 mph (35 knots/65 kmh). It was located 590 miles south of Karachi, Pakistan near 15.2 North and 67.8 East. 5A was moving to the northwest at 8 knots (9 mph/14 kmh) and generating seas of 17 feet (5.1 meters) high. Infrared imagery today shows that the banding of thunderstorms in the southeastern quadrant of the storm have thinned, a sign of weakening.

Forecasters say that it will track northwest across the Arabian Sea toward Somalia and strengthen a little more before running into wind shear that is expected to weaken the storm.

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