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Hurricane Season 2011: System 96P (South Pacific Ocean)
03.09.11
 
96P appears to have lost organization in circulation because of a nearby upper level low pressure area. › View larger image
When NASA's Aqua satellite passed over System 96P on March 9 at 02:17 UTC, most of the coldest, highest cloud tops and strongest thunderstorms (purple) were still east of Vanuatu, and the low appears to have lost organization in circulation because of a nearby upper level low pressure area. Northern New Zealand is seen bottom, center.
Credit: NASA/JPL, Ed Olsen
NASA Infrared Data Sees System 96P Being Ripped Apart

The low pressure area known as System 96P in the Southern Pacific has been dealt a blow from an increase in wind shear and the system is coming apart. NASA's Aqua satellite passed over System 96P early on March 9 and saw its low-level center was now ill-defined as a result of the battering winds.

The Atmospheric Infrared Sounder (AIRS) instrument that flies on Aqua captures infrared, visible and microwave (with the assistance of another instrument on Aqua) satellite imagery. Infrared data, which shows temperatures of cloud tops and sea surface temperatures showed that despite some strong convection in the low pressure area, an increase in wind shear over the last 24 hours from a nearby upper level trough (elongated area) of low pressure is basically tearing at the organization of the storm.

That upper level trough is not only producing wind shear, but also causing subsidence on the southwestern side of the low pressure area. Subsidence is the sinking of air from upper levels of the atmosphere to the surface and that prevents clouds from forming that create the thunderstorms that power a tropical cyclone.

The convection in System 96P has also decreased over the last 24 hours as AIRS showed that cloud top temperatures have warmed (the cloud tops are not as high as they were, and the higher the cloud top, the colder the temperature and vice-versa).

At 0600 UTC (1 a.m. EST) System 96P's poorly-defined center was about 340 miles west-southwest of Nadi, Fiji near 19.7 South and 171.8 East. The final warning from Vanuatu was issued on System 96P, and the Joint Typhoon Warning Center has downgraded their forecast for potential development of this low to "poor."

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

March 8, 2011

On March 8, most of the coldest, highest cloud tops and strongest thunderstorms were still over open waters. › View larger image
When NASA's Aqua satellite passed over System 96P on March 8, most of the coldest, highest cloud tops and strongest thunderstorms (purple) were still over open waters and east of Vanuatu.
Credit: NASA/JPL, Ed Olsen
NASA Infrared Satellite Data Sees System 96P Developing Tropically Near Vanuatu

The low pressure area called System 96P in the South Pacific appears to be getting organized in infrared satellite imagery from NASA. System 96P is showing signs of strong convection and that has prompted the government of Vanuatu to issue tropical cyclone warnings today.

Vanuatu is an island nation located in the South Pacific Ocean. A tropical cyclone warning is in effect today for the Sanma, Penama, Malampa and Shefa Provinces of Vanuatu. Strong winds and heavy surf are expected in the next 12 to 24 hours in the warning areas. Local updates are available on the Vanuatu Meteorological Service website at http://www.meteo.gov.vu.

At 0600 UTC (1 a.m. EST) on March 8, 2011, System 96P was located about 220 miles west-northwest of Vanuatu, near 16.3 South and 164.7 East. Maximum sustained winds are estimated between 20 and 25 knots (23 mph to 29 mph/37 kmh to 46 mph) with higher gusts.

When NASA's Aqua satellite passed over System 96P on March 8 at 14:05 UTC (9:05 a.m. EST) the Atmospheric Infrared Sounder (AIRS) instrument captured an infrared image of the storm's cloud temperatures. The imagery showed increased deep convection (rapidly rising air that forms the thunderstorms that make up a tropical cyclone) over a developing low level circulation center.

Despite some stronger convection, the western side of System 96P is in a region of high vertical wind shear. That wind shear is being generated by an upper-level low pressure area. Wind shear means winds that can weaken a tropical cyclone.

Cloud temperatures are a key in determining storm strength. The higher the cloud tops, the stronger the convection and the stronger the thunderstorms are that power a tropical cyclone. That's why infrared data from AIRS is so important to forecasters. AIRS data showed that most of the coldest, highest cloud tops and strongest thunderstorms were still east of the island nation at that time. The coldest cloud tops were as cold as or colder than -63 degrees Fahrenheit (-53 Celsius).

The Joint Typhoon Warning Center forecasters give System 96P a "fair" chance at becoming a tropical depression in the next 24 hours, but residents in the region of Vanuatu should make preparations now.

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