Science and Technology News

Monday, January 24, 2011

Hurricane Season 2011: Tropical Cyclone Wilma (Southern Pacific)

NASA Satellite Peels Back the Rain Envelope in Cyclone Wilma Over Samoa

NASA's TRMM satellite passed over Tropical Cyclone Wilma and "peeled back" the clouds of the storm to look into the rate in which rain was falling within the storm. Some areas were dropping heavy rain at more than 2 inches (50 mm) per hour.

A tropical disturbance west of Samoa became tropical Cyclone Wilma on January 22, 2011. At that time it was about 165 miles north-northwest of Pago Pago.

Currently, regional warnings are in effect for Tonga and Tokelau and for the Lau group of islands, Moala, Fiji. The cyclone may bring damaging winds to the Southern Lau group later today. Low level flooding is also likely in the warning areas.

Tropical Cyclone Wilma then buffeted Samoa with little damage and was moving toward the south when the Tropical Rainfall Measuring Mission (TRMM) satellite passed above on January 23, 2011 at 2046 UTC (3:46 p.m. EST). That image showed that skies were clearing over Samoa as Wilma's center had moved east. Wilma's scattered intense thunderstorms with rainfall over 50 mm/hour (~2 inches) were still embedded in the storm's main circulation over open ocean, particularly north and east of the center of circulation. TRMM is managed by both NASA and the Japanese Space Agency.

The National Weather Service in American Samoa reported sustained winds up to 60 mph with higher gusts occurred. Heavy rainfall also caused mudslides and some power outages were reported.

Microwave imagery today shows tightly curved bands of thunderstorms wrapping into the low-level center of the cyclone. The strongest convection and heaviest rainfall was occurring along the south and eastern edges of the center of circulation.

When NASA's Aqua satellite passed over Cyclone Wilma on January 24 at () the Atmospheric Infrared Sounder (AIRS) instrument captured an infrared image of its cloud top temperatures. The coldest cloud tops were as cold as or colder than -63 Fahrenheit/-53 Celsius indicating the strongest thunderstorms and areas of heavy rainfall. AIRS infrared data also showed that the highest, coldest cloud tops were around the center of circulation and in the eastern quadrant of the storm, paralleling the TRMM data that said heaviest rainfall was occurring in the eastern quadrant of the storm.

The Joint Typhoon Warning center forecasts Wilma to turn slowly southward and begin to weaken because of cooler sea surface temperatures.

By January 25 Wilma is predicted to intensify to a category one cyclone on the Saffir-Simpson scale with winds of about 70 knots (~80.5 mph) while moving toward the southwest. Wilma is then forecast to become extra-tropical. Current forecast tracks take Wilma toward Auckland, New Zealand by the end of this week.

Text Credit: Rob Gutro
NASA Goddard Space Flight Center, Greenbelt, MD

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