Hurricane Season 2011: System 91W (Northwestern Pacific Ocean)

NASA's Aqua Satellite Watching a Tropical Low in the South China Sea

A low pressure area designated as System 91W in the South China Sea has shown some bursts of strong convection, and an infrared instrument on NASA's Aqua satellite has been watching it for possible tropical development.

The South China Sea is part of the Pacific Ocean, that stretches from the Singapore and Malacca Straits to the Strait of Taiwan.

On Mar. 2 at 1753 UTC (12:53 p.m. EST), the Atmospheric Infrared Sounder (AIRS) instrument that flies aboard NASA's Aqua satellite captured what appeared to be a disorganized low pressure area with some strong areas of convection (rapidly rising air that condenses and forms the thunderstorms that power a tropical cyclone). AIRS measured the temperatures in those strong areas of convection and found they were as cold as or colder than -63 Fahrenheit (-52 Celsius). On March 3, at 0623 UTC (1:23 a.m. EST) caught the western edge of the low pressure area that appeared slightly more organized and rounded, as the Aqua satellite flew west of its center, however, convection seemed to be weaker.

System 91W is now about 340 nautical miles (629 km) northwest of Brunei, near 10.4 North latitude and 113.2 East longitude. NASA's AIRS imagery should that the low level circulation center became fully exposed mid-day today, March 3, 2011 (Eastern Standard Time), and convection had weakened from earlier satellite overpasses.

An upper level analysis from the Joint Typhoon Warning Center (JTWC) today indicated that the low-level center was in an area of moderate to high vertical wind shear, blowing at about 25 knots (29 mph/46 kmh). Wind shear weakens a tropical cyclone, or a low pressure area. Currently, the maximum sustained surface winds from System 91W were between 10 and 15 knots (11 to 17 mph/18 to 27 kmh. The JWTC currently gives System 91W a poor chance of becoming a tropical depression in the next 24 hours, but NASA's AIRS instrument will keep taking its temperatures to monitor its strength.

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