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Hurricane Season 2011: Tropical Storm 20S (South Pacific)
04.05.11
 
Tropical Cyclone 20S on April 2 when it was moving away from the coast and it was still a tropical storm. › View larger image
NASA's Terra satellite captured an image of Tropical Cyclone 20S on April 2 at 0205 UTC when it was moving away from the coast and it was still a tropical storm.
Credit: NASA MODIS Rapid Response Team
Remnants of Tropical Cyclone 20S Still Causing Strong Winds in Western Australia

A coastal waters wind warning is still in effect for Cape Leveque to Cape Preston in northern Western Australia today as the remnants of Tropical Cyclone 20S continue to move away from the coast.

Tropical Cyclone 20S is now a remnant low pressure area far north of Kimberley and combined with a strong high pressure system located to the south, strong northeasterly and southeasterly winds are expected south of the state is expected in that warning area today. Winds are expected between 20 and 30 knots (23-34 mph/37-55 kmh)Wednesday, with seas up to 6 feet (2 meters) and swells up to 3 feet (~ 1 meter), according to the Australian Bureau of Meteorology.

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



April 4, 2011

AIRS revealed one area to the east of the 20S's center still showed strong convection (purple). › View larger image
NASA's Aqua satellite AIRS instrument infrared imagery on April 3 at 0535 UTC revealed one area to the east of the storm's center that still showed strong convection (purple).
Credit: NASA/JPL, Ed Olsen
NASA Sees Tropical Storm 20S Weakening and Moving Away from Western Australia

Infrared satellite imagery from NASA on April third showed a weakened tropical storm 20S over northern Australia's coast. Although the infrared data showed some strong thunderstorms at that time they have since weakened and the system is now moving toward the open waters of the Indian Ocean.

System 91S had been affecting northern Australia since last week and over the weekend it strengthened into Tropical Storm 20S in the Timor Sea, made land along the northern coast and is now weakening on its way back to open waters while still dumping heavy rainfall to areas along the northern coast of Western Australia.

On April 3, Tropical Storm 20S was bringing rainfall, rough surf and gusty winds to the northeastern coast of Western Australia. It was near 13.5 South and 127.6 East. Infrared data from the Atmospheric Infrared Sounder (AIRS) instrument that flies aboard NASA's Aqua satellite revealed one area to the east of the storm's center that still showed strong convection on April 3. That area of strongest thunderstorms had cold cloud top temperatures of -63 F/-52 C indicating they were likely generating heavy rainfall at the time the image was captured (0535 UTC).

Tropical Storm 20S then tracked parallel to the northern Australian coast this weekend, triggering a cyclone warning for coastal areas from Wyndham to Beagle Bay and a watch for coastal areas from Beagle Bay to Bidyadanga, including Broome and Derby. All watches and warnings have since been dropped.

By Monday, April 4, the final warning on the once-tropical storm 20S was issued. At 1500 UTC the maximum sustained winds were down to 20 knots (23 mph/37 kmh). It was about 590 miles east-northeast of Learmonth, Australia near 16.3 South and 122.4 East. It was moving west-southwest near 5 knots (7 mph) and was a remnant low pressure area.

The Australian Bureau of Meteorology noted on April 4, that the low was close to the west Kimberley coast north of Cape Leveque. It is forecast move further offshore overnight and during Tuesday, but will bring heavy rainfall to parts of the Kimberley overnight and during Tuesday on its way toward the open waters of the Indian Ocean.

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



April 1, 2011

Imagery from the Meteosat-2 to provide a complete picture of the low pressure areas cloud extent and rainfall rates. › View larger image
TRMM imagery was overlaid on top of infrared imagery from the Meteosat-2 to provide a complete picture of the low pressure areas cloud extent and rainfall rates. TRMM's precipitation radar instrument measured rainfall rates close to 1 inch/25 mm (yellow) per hour.
Credit: Navy/NRL/NASA
NASA's TRMM Satellite Sees Tropical Depression 91S Soaking Northern Australian Coastline

Australia's Northern Territory has been experiencing rainfall and winds from the low pressure system called "System 91S" for several days this week. Today, NASA's Tropical Rainfall Measuring Mission satellite spotted light to moderate rainfall in the system as continues tracking southwest and bringing rains and winds to the northern coast of Western Australia this weekend.

System 91S was located in the Timor Sea, west-southwest of Darwin, Australia (Northern Territory) and was moving in a west-southwesterly direction. System 91S is forecast to continue traveling in that direction and its center is expected to remain at sea over the next several days as it heads toward the Southern Indian Ocean.

As it continues to track along coastal areas of the Northern Territory and Western Australia, cyclone warnings are in effect. A Cyclone Warning is in effect for Western Australian coastal and island areas from Kuri Bay to the Western Australia/Northern Territory border, including Kalumburu and Wyndham. In addition, a cyclone watch is in effect from Kuri Bay to Cape Leveque, not including Derby.

The TRMM satellite, operated by both NASA and the Japanese Space Agency, passed over the system at 1451 UTC on April 1. The U.S. Navy and Naval Research Laboratory's Monterey Marine Meteorology Division, Calif. overlaid TRMM rainfall rate imagery on top of Japan's METSAT-2 infrared imagery to provide a complete picture of the low pressure areas cloud extent and rainfall rates. TRMM's precipitation radar instrument measured rainfall rates close to 1 inch (25 mm) per hour.

Surface winds on April 1 are estimated between 25 and 30 knots (29 to 34 mph / 46 to 55 kmh). Satellite imagery indicated that the center of Depression 91S' circulation was located near 13.2 South latitude and 128.9 East longitude. It is moving in a southwesterly direction near 4 knots (5 mph/7 kmh).

Infrared satellite imagery shows that the low-level center of circulation appears to be consolidating, and there is improved banding of thunderstorms wrapping into the center of the storm. Both of those factors hint at a storm organizing and strengthening. The only challenge in the forecast is that there is a moderate wind shear battering the storm which is inhibiting further strengthening into a tropical storm today. That vertical wind shear is expected to decrease as System 91S tracks along the northern coast this weekend.

There is a good chance that System 91S could become a tropical storm over the weekend. Regardless, residents of the northern coastal areas of Western Australia should expect some heavy rainfall, gusty winds and rough surf at the beaches this weekend.

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



March 30, 2011

System 90S, located about 500 miles north-northwest of Port Hedland, Australia. › View larger image
The TRMM satellite measured rainfall rates between 5 and 20 millimeters (0.2 and 0.8 inches) per hour (blue and yellow) within the System 90S, located about 500 miles north-northwest of Port Hedland, Australia.
Credit: NASA/SSAI, Hal Pierce
System 99S, located about 500 miles north of the Cocos Islands › View larger image
The TRMM satellite measured rainfall rates between 5 and 20 millimeters (0.2 and 0.8 inches) per hour (blue and yellow) within the System 99S, located about 500 miles north of the Cocos Islands today.
Credit: NASA/SSAI, Hal Pierce
There are four low pressure areas in the tropics today that NASA satellites are all keeping an eye on for possible development. They are Systems 90S, 91S and 99S in the Southern Pacific, and System 93B in the Northern Indian Ocean. Despite a poor chance for development in all of them, one has triggered warnings in northern Australia because of its proximity to land.

NASA and the Japanese Space Agency manage the Tropical Rainfall Measuring Mission or TRMM satellite and TRMM passed over two of those four systems today. TRMM captured light to moderate rainfall in the low pressure area called "System 90S" on March 30 at 01:49 UTC. Rainfall rates were between 5 and 20 millimeters (0.2 and 0.8 inches) per hour within the storm. System 90S is located 500 miles north-northwest of Port Hedland, Australia, near 12.0 South latitude and 116.0 East longitude.

Infrared satellite imagery from the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA's Aqua satellite revealed that the low has consolidated during the morning hours, while the Advanced Microwave Scanning Radiometer-E instrument showed deep convection on the north and south sides of the center of circulation. Despite these developments atmospheric dynamics are not currently favorable, so the Joint Typhoon Warning Center currently gives this low a poor chance for development.

The second tropical low pressure area NASA satellites are watching is also 500 miles away from land, and that's System 99S. System 99S is 500 miles north of the Cocos Islands today, near 9.8 South and 99.4 East. The TRMM satellite measured rainfall rates between 5 and 20 millimeters (0.2 and 0.8 inches) per hour within the System 99S early today. The AIRS infrared imagery captured from NASA's Aqua satellite shows that areas of deep convection exist on all sides of the low pressure center, but it's not uniform. Vertical wind shear is currently light and sea surface temperatures are warm enough to support development, however, the chance that it will develop into a tropical storm in the next 24 hours is poor. As the week progresses, perhaps the chance will improve with the environmental conditions.

The third tropical low pressure area isn't a tropical storm but it has triggered a watch for Australia's Northern Territories. Because of System 91S' location, about 200 miles northeast of Darwin, Australia (near 10.0 South and 133.1 East), a tropical cyclone Watch has been issued for the coastal communities between Cape Hotham, Port Keats, including Darwin and the Tiwi Islands. The Tiwi Islands include Melville and Bathurst Islands and are part of Australia's Northern Territory, 25 miles (40 km) north of Darwin where the Arafura Sea joins the Timor Sea. In addition, a Strong Wind Warning has been issued from Milingimbi to Troughton Island.

System 91S is expected to move in a southwesterly direction over the next several days and track over Snake Bay, Mellville Island and Cape Fourcroy, Bathurst Island.

NASA AIRS infrared imagery revealed today that the convection (rapidly rising air that produces the thunderstorms that power a tropical cyclone) are intensifying and expanding around System 91S' center. The convection, however appears disorganized in the low and the maximum sustained winds are between 15 and 20 knots (17-23 mph/27-37 kmh). The chance for development into a tropical storm in the next 24 hours remains poor, but the areas under the watch may feel System 91S' rains and some gusty winds.

The fourth area is in the northern hemisphere and in a different ocean. Tropical low 93B is located in the Northern Indian Ocean. Last night it was only 50 miles north of Phuket, Thailand near 9.0 North latitude and 98.7 East longitude. However, today, infrared satellite imagery from NASA's AIRS instrument showed that the low level circulation center has drifted inland. When a low is inland, its center of circulation is cut off from the warm waters that power the tropical cyclone. Because of weak steering winds, however, the low may move back seaward and redevelop in the warm waters offshore.

Currently the system's maximum sustained winds are between 15 and 20 knots (17-23 mph/27-37 kmh). The chance for development into a tropical storm in the next 24 hours remains poor, but coastal Thailand are already experiencing rains and some gusty winds from System 93B.

NASA's TRMM and Aqua satellites continue to provide data to forecasters who are keeping a watchful eye on all of these tropical low pressure areas.

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