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Hurricane Season 2009: Etau (Western Pacific)
August 12, 2009

Tropical Storm Etau being undergoing a transition into an extra-tropical storm. > View larger image
NASA's AIRS instrument captured this visible image of Tropical Storm Etau being stretched out from northeast to southwest while undergoing a transition into an extra-tropical storm.
Credit: NASA/JPL, Ed Olsen
Etau Exiting as Extra-Tropical

Tropical Storm Etau is making its exit in this world as an extra-tropical cyclone today, August 12, and NASA's Aqua satellite imagery provided a visual confirmation that the storm is stretching out and weakening.

NASA's Aqua satellite flew over Etau on August. 11 at 10:23 p.m. EDT and its Atmospheric Infrared Sounder (AIRS) instrument captured a visible image of the storm. The image showed that Etau's clouds were being "stretched" from northeast to southwest, indicating that the storm is becoming more frontal in nature (like a cold or warm front). Meanwhile, Etau is also losing its tropical characteristics and becoming extratropical. By the end of the day today, August 12, Etau will have made the complete conversion.

A conversion to "extratropical" status means that the area of low pressure (Etau in this case) eventually loses its warm core and becomes a cold-core system. During the time it is becoming extratropical the cyclone's primary energy source changes from the release of latent heat from condensation (from thunderstorms near the storm's center) to baroclinic (temperature and air pressure) processes. When a cyclone becomes extratropical it will usually connect with nearby fronts and or troughs (extended areas of low pressure) consistent with a baroclinic (pressure) system. When that happens it appears the system grows larger while the core weakens.

The last position on Etau was about 580 miles east-southeast of Tokyo, Japan, near 32.8 north and 150.9 east. That was at 5 a.m. EDT today, August 12. The storm was moving east-northeast, and staying away from land areas. It's moving around the edge of an elongated high pressure system in the Western Pacific Ocean.

Etau's circulation is partially exposed, and exposure is a bad thing for a tropical cyclone. That means winds or dry air can filter into the storm's center and weaken it quickly. Etau is also exposed to stronger westerly winds which are working against the storm.

By the day's end, Etau will be known as "Etau the Extra-tropical."

Text credit: Rob Gutro, NASA's Goddard Space Flight Center

August 11, 2009

Tropical Storm Etau moving away from Japan on August 10 at 11:23 p.m. EDT. > View larger image
This visible image from NASA's AIRS instrument shows Tropical Storm Etau moving east and away from Japan on Aug. 10 at 11:23 p.m. EDT.
Credit: NASA/JPL, Ed Olsen
NASA Satellite Sees Tropical Storm Etau Moving Away from Japan

NASA satellite imagery has provided relief to residents of east central Japan because it shows that Tropical Storm Etau is already moving away from Japan.

A visible image from NASA's Atmospheric Infrared Sounder (AIRS) instrument captured Tropical Storm Etau moving east and away from Japan on August 10 at 11:23 p.m. EDT (August 11, 0323 UTC). AIRS is an instrument that flies aboard NASA's Aqua satellite.

By 11 a.m. EDT on August. 11, Tropical Storm Etau had moved to a position 210 miles southeast of Toyko, Japan, near 33.2 north and 144.0 east. It was moving east near 19 mph, and kicking up 16 foot-high waves.

Etau is forecast to continue moving east, then turn to the east-northeast over the next couple of days into the open waters of the Western Pacific Ocean. Etau is expected to become extra-tropical at sea by Thursday, August 13.

Text credit: Rob Gutro, NASA's Goddard Space Flight Center

August 10, 2009

Cyclone Morakot's rainfall from August 3-10. > View larger image or > View video
This animation from the TRMM satellite from August 3-10 shows Typhoon Morakot move through the eastern China Sea, and near the end of the video, Tropical Depression Etau forms and brings heavy rains to southern Japan.
NASA Satellite Sees Tropical Depression Etau Drench Japan

Tropical depressions can bring a lot of rainfall, and the Tropical Rainfall Measuring Mission satellite watched Etau do just that to Japan over the last day. Depressions don't have to grow into hurricanes to bring flooding rains, and Tropical Depression Etau, currently skirting Japan's east coast, continues to dump lots of rainfall and has already taken lives there.

On Monday, August 10 at 11 a.m. EDT, Etau was located about 345 miles southwest of Toyko near 32.0 north and 136.7 east. Its maximum sustained winds were near 33 mph, and it was moving northeasterly near 13 mph, skirting Japan's coast. Etau is expected to transition to an extra-tropical system but will maintain its sustained wind speed.

The TRMM satellite, managed by NASA and the Japanese Space Agency can measure rainfall from space. TRMM data, along with information from other satellites, allows researchers to see how much rain is falling over most of the world every three hours and map areas of potential flooding. Maps that show areas of potential floods use precipitation radar data and high resolution measurements of water content of clouds made by microwave radiometers.

Those rainfall maps are also made into a seven-day "movie loop" that allows users to track storms as they travel over land and oceans around the globe. The rainfall animations are developed in the Laboratory for Atmospheres of the NASA Goddard Space Flight Center, Greenbelt, Md. by the TRMM precipitation research team.

The Sydney Morning Herald reported that heavy rains from Etau had flooded over 500 homes and evacuated 2,200 people. Eleven people have been killed by flood waters or landslides that resulted from the heavy rains.

Forecasters expect that once Etau parallels Toyko (while remaining at sea) it will turn more easterly and head out to the open waters of the western Pacific Ocean.

For more information about how TRMM looks at rainfall, visit NASA's TRMM website at: http:http://trmm.gsfc.nasa.gov/. TRMM is a joint mission between NASA and the Japanese space agency JAXA.

Text credit: Rob Gutro, NASA's Goddard Space Flight Center