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Hurricane Season 2012: Tropical Storm Kuena (Southern Indian Ocean)
06.08.12
 
TRMM satellite show how Kuena's intensity waned between June 6 (left) and June 7 (right). › View larger image
These two images of Kuena's rainfall from NASA's TRMM satellite show how the intensity waned between June 6 (left) and June 7 (right). The yellow, green and blue areas indicate light-to-moderate rainfall between 20 and 40 millimeters (.78 to 1.57 inches) per hour. The red area is considered heavy rainfall at 2 inches/50 mm per hour. There were no areas of heavy rain on June 7 as the system continued to weaken. Kuena's past and forecast track is shown overlaid in white on the left image.
Credit: ASA/SSAI, Hal Pierce
TRMM data shows that a few powerful storms within Kuena were pushing to heights above 15km (~9.3 miles). › View larger image
A 3-D analysis of Kuena's vertical structure using TRMM data from June 6 at 1607 UTC shows that a few powerful storms within Kuena were pushing to heights above 15km (~9.3 miles). The yellow, green and blue areas indicate light-to-moderate rainfall between 20 and 40 millimeters (.78 to 1.57 inches) per hour. The red area is considered heavy rainfall at 2 inches/50 mm per hour.
Credit: NASA/SSAI, Hal Pierce
Tropical Depression Keuna's Rainfall Weakens

The Tropical Rainfall Measuring Mission satellite called TRMM measures how much rain can fall per hour in storms. Between June 6 and 7, TRMM noticed the rainfall rate within Tropical Depression Kuena had lessened.

A tropical storm called Kuena formed in the southwest Indian Ocean east of Madagascar on June 6, 2012. This is a little unusual because the tropical cyclone season in that area normally ends on May 15, although two tropical storms formed in the north Atlantic this year before that season even officially started, so tropical cyclones seem to be ignoring the calendar this year.

The TRMM satellite had an excellent view of Kuena when it flew directly above the newly formed storm on June 6, 2012 at 1607 UTC. A rainfall analysis was made at NASA's Goddard Space Flight Center in Greenbelt, Md. that used data from TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) instruments. That analysis was overlaid on an enhanced infrared image from TRMM's Visible and InfraRed Scanner (VIRS) instrument and showed heavy convective storms were dropping intense rainfall of over 50mm/hr (~2 inches) within the storm. A 3-D analysis of Kuena's vertical structure showed that a few of these powerful storms within Kuena were pushing to heights above 15km (~9.3 miles).

The TRMM satellite had another fairly good look at Kuena on June 7, 2012 at 0158 UTC. Data from TRMM's TMI instrument shows that Kuena was producing moderate rainfall over a large area of the south Indian Ocean east of Madagascar. There were no areas of intense rainfall on June 7, as there were on June 6.

At 1500 UTC (10 a.m. EDT) on June 7, the Joint Typhoon Warning Center noted that the last position of the low's center was near 8.7 South latitude and 55.5 East longitude. It was moving in a northwest direction as it continued weakening until it dissipated under strong wind shear conditions.

Text Credit: Hal Pierce/Rob Gutro
SSAI/NASA Goddard Space Flight Center, Greenbelt, Md.















June 7, 2012
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 Olsen
NASA 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.





June 6, 2012
This visible image of Kuena revealed an organized story with banding of thunderstorms east of the center of circulation. › View larger image
NASA’s Aqua satellite passed over the eastern half of newborn Tropical Storm Kuena on June 6, 2012 at 0909 UTC (5:09 a.m. EDT). The visible image revealed an organized story with banding of thunderstorms east of the center of circulation. No eye was visible yet, however.
Credit: NRL/JTWC/NASA
Tropical Storm Kuena Forms in Southern Indian Ocean

Tropical Storm Kuena has formed east of the northern tip of Madagascar today and NASA’s Aqua satellite captured the eastern half of the storm.

NASA’s Aqua satellite passed over the eastern half of newborn Tropical Storm Kuena on June 6, 2012 at 0909 UTC (5:09 a.m. EDT). The visible image, taken by the Moderate Resolution Imaging Spectroradiometer or MODIS instrument onboard Aqua, revealed an organized story with banding of thunderstorms east of the center of circulation. No eye was visible yet, however.

Kuena has maximum sustained winds near 35 knots (40 mph/64.8 kph) and was moving to the west at 9 knots (10.3 mph/16.6 kph). It was about 600 nautical miles east-northeast of Madagascar near 9.3 South and 59.3 East. The current forecast track takes Kuena near Agalega and Seychelles.

Agalega is made up of two small islands and is located about 697 miles (1122 km) north of Mauritius. Seychelles includes an archipelago of 115 islands, located northeast of Madagascar.

Kuena is expected to move west and intensify slightly before weakening later this week.

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