Hurricane Season 2011: Tropical Cyclone Cherono (Southern Indian Ocean)

A 3-D Look at Tropical Storm Cherono from NASA Shows Strengthening

NASA's Aqua and TRMM satellites have noticed that thunderstorms are higher and stronger and rainfall has increased as Tropical Depression 18S became Tropical Storm Cherono in the Southern Indian Ocean today. NASA satellite data was used to create a 3 dimensional image of Cherono that showed powerful towering thunderstorms near its center that indicated it was strengthening.

On March 17, 2011 at 0212 UTC the Tropical Rainfall Measuring Mission (TRMM) satellite passed over tropical cyclone 18S (later named Cherono) that had formed and was intensifying in the open waters of the South Indian Ocean. 18S was already well organized and TRMM's Precipitation Radar (PR) showed that powerful thunderstorm towering clouds were located near 18S' center of circulation. These towering clouds know as chimney clouds or hot towers release a lot of energy and can serve to strengthen a tropical cyclone.

The TRMM data was used to put together an image of the strengthening storm in 3-D by Hal Pierce of the NASA TRMM Team at NASA's Goddard Space Flight Center in Greenbelt, Md. The 3-D image revealed that then Tropical Cyclone 18S had towering clouds or "hot towers" over 15 kilometers (9 miles) high! Those high hot towers were an indication of a strong and strengthening storm, and the next day, March 18, Cyclone 18S strengthened into Tropical Storm Cherono. The data for the image was captured by the TRMM satellite as it passed above on March 17 at 0212 UTC.

TRMM also captured the rainfall within Tropical Cyclone 18S showed that much of the rainfall occurring within the tropical cyclone was moderate, falling at a rate between 20 and 40 mm (.78 and 1.57 inches) per hour. There were some areas within the storm, however, where heavy rain was falling at a rate of 50 mm (2 inches) per hour. At the time TRMM passed, 18S was expected to attain strong tropical storm intensity and it did early this morning, March 18.

TRMM images are pretty complicated to create. At Goddard, rain rates in the center of the swath (the satellite's orbit path over the storm) are created from the TRMM PR instrument. The TRMM PR is the only space borne radar of its kind. The rain rates in the outer portion of the storm are created from a different instrument on the satellite, called the TRMM Microwave Imager. The rain rates are then overlaid on infrared data from the TRMM Visible Infrared Scanner. For more information about TRMM, visit: http://www.trmm.gsfc.nasa.gov/.

NASA's Aqua satellite passed over Tropical Cyclone 18S (now Cherono) on March 17 at 20:35 UTC and the Atmospheric Infrared Sounder (AIRS) instrument onboard captured an infrared image of the storm. The AIRS data showed strong convection (rapidly rising air that forms the thunderstorms that make up a tropical cyclone) with cloud top temperatures as cold as -52C/-63F confirming the hot tower clouds seen in the TRMM satellite data. The infrared data from AIRS also showed that bands of thunderstorms were wrapping into the center of the storm and that Cherono had taken on more of a signature shape of a developed tropical storm.

On March 18 at 0900 UTC, Tropical Storm Cherono had maximum sustained winds near 45 knots (52 mph/ 83 kmh). Tropical storm-force winds (winds of 34 knots/39 mph/63 kmh and higher) extended out 80 miles (128 km) from the center. Cherono's center of circulation was about 515 miles (828 km) south-southeast of Diego Garcia, near 16.5 South latitude and 72.4 East longitude. It was moving to the west-southwest near 10 knots (11 mph/18 kmh) and generating 17-foot (5 meter) high seas.

By the end of the weekend, Cherono is expected to start moving past Port Louis and La Reunion Island. Its center and strongest winds are expected to remain at sea; however, those islands will likely receive some heavy rainfall, gusty winds and strong surf on the islands east and south sides.

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