Hurricane Season 2011: System 93W (Western North Pacific Ocean)

Tropically-Speaking - NASA Satellite Imagery Shows Big System 93W Developing

System 93W is a large low pressure area in the Western North Pacific Ocean that appears poised for tropical development in NASA satellite imagery. Improved circulation and warm sea surface temperatures provide some hints of a strengthening storm.

The Atmospheric Infrared Sounder (AIRS) instrument that flies aboard NASA's Aqua satellite captured both an infrared and visible image of System 93W on May 4 at 01:53 UTC (May 3 at 9:53 p.m. EDT). The width of the AIRS image track is 1056 miles (1700 km), the width of System 93W appears to be approximately 800 miles (1,287 km) from west to east.

The AIRS imagery showed an improved low-level circulation center and unorganized, but deep convection. Convection is rapidly rising air that forms the thunderstorms that power a tropical cyclone.

The strongest convection appeared around the center of System 93W's circulation where cloud-top temperatures were measured to be as cold as or colder than -63F/-52C. Cloud-top temperatures are important because they tell forecasters how high thunderstorms are, and the higher the thunderstorm, the colder the cloud tops and the more powerful the thunderstorms.

Today, May 4, the low pressure area was located about 180 nautical miles east of Mindanao, the Philippines today, near 9.4 North and 129.0 East. Its surface winds are estimated between 15 and 20 knots. The system is moving west-northwestward at 11 knots (~12 mph/20 kmh).

The Joint Typhoon Warning Center (JTWC) noted that a buoy about 100 nautical miles to away reported a minimum central pressure of 1005 millibars. With sea surface temperatures near 84F (29C), the waters are warm enough to support development into a tropical storm. Wind shear is also low, which will help with development. The JTWC gives System 93W a good chance for development into a tropical storm over the next 24 hours.