Hurricane Season 2012: Tropical Storm Kuena (Southern Indian Ocean)
06.07.12
 
MODIS capture this image of Tropical Storm Kuena in the Indian Ocean on June 6, 2012 at 06:20 UTC (2:20 a.m. EDT/U.S.)› View larger image
This image of Tropical Storm Kuena in the Indian Ocean was captured by the MODIS instrument on NASA's Terra satellite on June 6, 2012 at 06:20 UTC (2:20 a.m. EDT/U.S.) before it weakened to a tropical depression.
Credit: NASA/Goddard MODIS Rapid Response Team
AIRS revealed that the area of strong thunderstorms (purple) and coldest cloud top temperatures had grown smaller since June 6› View larger image
NASA's Aqua satellite also passed over Tropical Depression Kuena and the AIRS instrument onboard provided an infrared look at the cloud temperatures. It revealed that the area of strong thunderstorms (purple) and coldest cloud top temperatures had grown smaller since June 6, and were mostly confined to the southeastern quadrant.
Credit: NASA/JPL, Ed OlsenNASA Sees Tropical Depression Kuena Weakening from Wind Shear

Infrared satellite data provides meteorologists with a "look under the hood" of a tropical cyclone by providing cloud top temperatures. Cloud top temperatures appeared to be warming in tropical storm Kuena in NASA satellite imagery today, indicating that the strength was going out of the storm, and cloud heights were dropping. Wind shear is also pushing the strongest thunderstorms away from Kuena's center, and the storm weakened to tropical depression status.

The higher a cloud top is in the atmosphere, the colder it is, as temperatures drop higher up in the troposphere (the lowest atmospheric level where weather happens). So, very cold cloud tops indicate strong uplift of air occurring in a tropical cyclone, which helps build stronger thunderstorms, and a tropical cyclone is made up of hundreds of thunderstorms. Those stronger thunderstorms usually have heavy rainfall.

When NASA's Aqua satellite passed over Tropical Depression Kuena and the AIRS (Atmospheric Infrared Sounder) instrument onboard provided an infrared look at the cloud temperatures. It revealed that the area of strong thunderstorms and coldest cloud top temperatures had grown smaller since June 6, and were mostly confined to the southeastern quadrant. That's indicative that the power is going out of the system. That convection and area of strongest thunderstorms have been pushed over 150 nautical miles from the center of the system as a result of strong wind shear from the northwest.

On June 7 at 1500 UTC (10 a.m. EDT/U.S.), Tropical Depression Kuena had maximum sustained winds near 30 knots (35 mph/55.5 kph). It was located near 8.6 South latitude and 55.2 East longitude about 240 nautical miles (276.2 miles/444.5 km) south of the Seychelles in the Southern Indian Ocean. Kuena is moving to the northwest at 6 knots (7 mph/11.1 kph).

As Kuena keeps moving to the northwest, wind shear is expected to increase and that's going to prevent strong convection (rising air that forms thunderstorms) from occurring, sapping more of the storm's strength. The depression is expected to dissipate over the next couple of days.

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