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Hurricane Season 2011: Arani (South Atlantic Ocean)
03.18.11
 
TRMM showed that much of the rainfall occurring within Arani was falling at a rate of less than 10 mm (0.4 inches) per hour. › View larger image
The TRMM satellite captured rainfall rates within Tropical Depression Arani on March 17 at 0958 UTC. TRMM showed that much of the rainfall occurring within the tropical cyclone was light (blue), falling at a rate of less than 10 mm (0.4 inches) per hour. There were very small areas of moderate rain (yellow and green), falling at a rate between 20 and 40 mm (.78 and 1.57 inches) per hour and one small isolated area of heavy rain (red) falling at a rate of 50 mm (2 inches) per hour.
Credit: NASA/SSAI, Hal Pierce
NASA's TRMM Satellite Sees the Last of Rare Sub-Tropical Cyclone Arani

The Tropical rainfall Measuring Mission satellite known as TRMM captured the last bursts of rainfall from the Southern Atlantic Ocean's rare Sub-tropical Cyclone Arani yesterday.

The TRMM satellite captured rainfall rates within Tropical Depression Arani on March 17 at 0958 UTC. TRMM showed that much of the rainfall occurring within the tropical cyclone was light, falling at a rate of less than 10 mm (0.4 inches) per hour. There were very small areas of moderate rain, falling at a rate between 20 and 40 mm (.78 and 1.57 inches) per hour and one small isolated area of heavy rain falling at a rate of 50 mm (2 inches) per hour. TRMM is managed by NASA and the Japanese Space Agency, JAXA.

Arani was quickly fading several hundred miles east of Brazil in the Southern Atlantic Ocean.

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









March 17, 2011

Purple areas north and east of the Ariani's center represent very high, cold, thunderstorm cloud tops. › View larger image
On March 16 at 15:53 UTC (1:52 p.m. EST) NASA's Aqua satellite flew over Sub-Tropical Storm Arani in the Southern Atlantic and captured some remaining cold, strong thunderstorms (purple) north and east of the storm's center. Those areas represent very high, cold, thunderstorm cloud tops where temperatures are as cold as or colder than -63F/-52C.
Credit: NASA/JPL, Ed Olsen
NASA Sees Sub-Tropical Storm Arani Merging With a Front

Sub-Tropical Storm Arani is now merging with a weather front and going out with a bang, according to NASA satellite imagery. Infrared imagery from NASA's Aqua satellite still showed some powerful thunderstorms in the system.

On March 16 at 15:53 UTC (1:52 p.m. EST) NASA's Aqua satellite flew over Sub-Tropical Storm Arani in the Southern Atlantic. The Atmospheric Infrared Sounder (AIRS) instrument captured some remaining cold, strong thunderstorms north and east of the storm's center at that time. Those areas represent very high, cold, thunderstorm cloud tops where temperatures are as cold as or colder than -63F/-52C, and were areas of heavy rainfall.

Although Sub-Tropical Storm Arani is located several hundred miles east of Rio de Janiero, it was still bringing heavy surf to beaches. Arpoador Beach reported rough surf on March 16 from Arani as it continued to move east and away from Brazil. Arani is now in the process of merging with a cold front and joining several other rare tropical cyclones in the history of the Southern Atlantic.

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



March 16, 2011

This 3-D view of Sub-tropical Storm Arani's clouds was created from data taken by NASA's TRMM satellite. › View larger image
This 3-D view of Sub-tropical Storm Arani's clouds was created from data taken by NASA's TRMM satellite. It showed that there were very heavy thunderstorms (red) in the eastern half of the storm. TRMM's Precipitation Radar showed that some of these powerful storms were reaching to heights of over 14 km (~8.7 miles) above the surface of the Southern Atlantic Ocean.
Credit: NASA/SSAI, Hal Pierce
TRMM had another very good view of Arani in the morning light on March 16, 2011 at 1052 UTC. › View larger image
The TRMM satellite had another very good view of Sub-tropical Cyclone Arani in the morning light on March 16, 2011 at 1052 UTC. This data showed that there were very heavy thunderstorms in the eastern half of the storm. TRMM's Precipitation Radar showed that some of these powerful storms were reaching to heights of over 14 km (~8.7 miles) above the surface of the Southern Atlantic Ocean.
Credit: NASA/SSAI, Hal Pierce
AIRS captured an infrared image of Arani's cold thunderstorm cloud tops in two areas of the storm. › View larger image
On Mar. 16 at 03:29 UTC (Mar. 15 at 11:29 p.m. EST) NASA's Aqua satellite captured an infrared image of Sub-Tropical Storm Arani's cold thunderstorm cloud tops (purple) in two areas of the storm. Those cloud tops were as cold as or colder than -63F/-52 C, and were areas of heavy rainfall. The strongest thunderstorms appeared north and south of the center of circulation.
Credit: NASA/JPL, Ed Olsen
TRMM measured the rainfall rates within Sub-Tropical Storm Arani on March 15 at 1820 UTC (2:20 p.m. EST). › View larger image
TRMM measured the rainfall rates within Sub-Tropical Storm Arani on March 15 at 1820 UTC (2:20 p.m. EST). TRMM rainfall images are false-colored with yellow, green and red areas, which indicate rainfall between 20 and 40 millimeters (.78 to 1.57 inches) per hour. Dark red areas are considered heavy rainfall, as much as 2 inches of rain per hour.
Credit: NASA/SSAI, Hal Pierce
NASA Satellites Show Towering Thunderstorms in Rare Sub-tropical Storm Arani

NASA's Aqua and TRMM satellites are providing data to scientists about the Southern Atlantic Ocean Sub-tropical Storm Arani, a rare occurrence in the southern ocean. Rainfall data and cloud top temperatures revealed some heavy rain and strong thunderstorms exist in Arani as it continues to pull away from Brazil.

NOAA's Satellite and Information Service classified Arani as a T1 on the Dvorak intensity scale which would indicate an estimated wind speed of about 29 knots (~33 mph).

During the daytime on Tuesday, March 15 at 1820 UTC (2:20 p.m. EST) NASA's Tropical Rainfall Measuring Mission (TRMM) satellite flew over Sub-Tropical Storm Arani. TRMM rainfall data showed that the storm contained mostly moderate rainfall, falling at a rate between 20 and 40 millimeters (.89 to 1.57 inches) per hour. However, there were some areas of heavy rainfall in the north and eastern quadrants of the storm. The heavier rainfall was occurring at about 50 mm or 2 inches per hour. TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) data were used in the image above to show rainfall near Arani.

On Mar. 16 at 03:29 UTC (Mar. 15 at 11:29 p.m. EST) another of NASA's fleet of Earth science satellites flew over Sub-tropical Storm Arani and took its temperature. NASA's Aqua satellite captured an infrared image of Sub-Tropical Storm Arani's cold thunderstorm cloud tops in two areas of the storm. The Atmospheric Infrared Sounder (AIRS) instrument that flies aboard Aqua provided infrared readings of those cloud tops and showed that they were as cold as or colder than -63F/-52 C, and were areas of heavy rainfall. The strongest thunderstorms wrapped from the north, eastward to the south of the center of circulation, confirming the data from the TRMM satellite.

Later on March 16, at 10:52 UTC (6:52 a.m. EST), the TRMM satellite again passed over Sub-Tropical Storm Arani and noticed it still had some strong thunderstorms and was producing heavy rainfall off the Brazilian coast.

TRMM data was used to create a 3-D view of Sub-tropical Storm Arani's clouds, and it showed that there were very heavy thunderstorms in the eastern half of the storm. TRMM's Precipitation Radar showed that some of these powerful storms were reaching to heights of over 14 km (~8.7 miles) above the surface of the Southern Atlantic Ocean.

Arani has the appearance of a tropical cyclone but has been classified as a subtropical cyclone. Subtropical cyclones are low pressure areas that develop with a cold core and transition to a warm core in the mid-levels of the troposphere, resembling a tropical cyclone. They more typically form outside of hurricane season (which is June 1 to Nov. 30 in the Northern Atlantic, for example). They also have broad wind patterns and that means that their maximum sustained winds are usually located farther from the center than a tropical cyclone. They also have no weather fronts linked to them, such as a typical low pressure area that brings summertime storms with an associated cold front. Subtropical cyclones can sometimes become tropical cyclones, and occasionally, tropical cyclones can become subtropical.

Tropical cyclones are very rare in the Southern Atlantic Ocean. In 2004 a cyclone called Catarina formed in the South Atlantic and caused some controversy when it was classified as a hurricane by the United States' National Hurricane Center.

Arani is over the open waters of the Southern Atlantic and continues to move east-southeast and farther away from Brazil.

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



























March 15, 2011

AIRS image of System 90L › View larger image
On March 14 at 1553 UTC (11:53 a.m. EST) NASA's Aqua satellite captured an infrared image of Sub-Tropical Storm Arani along the Brazilian coast. Most of the convection and thunderstorms (purple) were limited to the eastern half of the storm.
Credit: NASA JPL, Ed Olsen
NASA's Aqua Satellite Spots Rare Southern Atlantic Sub-Tropical Storm

NASA's Aqua satellite spotted some strong convection in a recently formed low pressure area that strengthened into Sub-Tropical Storm Arani in the South Atlantic. Arani formed near the coast of Brazil and is now moving away from it. Tropical cyclones in the Southern Atlantic are a rare occurrence and since 2004 there have only been three of them, Arani being the third.

On March 14, 2011 at 1553 UTC (11:53 a.m. EST) the Atmospheric Infrared Sounder (AIRS) instrument that flies aboard NASA's Aqua satellite captured an infrared image of Sub-Tropical Storm Arani moving away from the Brazilian coast. Most of the convection and thunderstorms were limited to the eastern half of the storm at the time of the image. The strong areas of convection (rapidly rising air that condenses and forms the thunderstorms that power a tropical cyclone) appeared on the imagery as a sideways boomerang, and were off-shore, paralleling the coast.

AIRS measured the temperatures in those strong areas of convection and found they were as cold as or colder than -63 Fahrenheit (-52 Celsius) indicating some strong thunderstorms with heavy rainfall. That heavy rainfall was occurring off-shore. NASA's AIRS imagery is created at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

On March 15 at 1500 UTC (11 a.m. EST), the Brazilian Navy issued a special marine warning for the Brazilian coast. The warning stated that Sub-Tropical Storm Arani was located near 24.0 South latitude and 37 West longitude. Arani had a minimum central pressure of 998 millibars and was moving east-southeast near 10 to 15 knot winds.

Tropical cyclones in the Southern Atlantic Ocean are rare. In 2010 System 90Q formed in the same region where Sub-Tropical Storm Arani formed this year. For more information on System 90Q, visit NASA's Hurricane page archives at: http://www.nasa.gov/mission_pages/hurricanes/archives/2010/h2010_90Q.html.

Dr. Jack Beven of the National Hurricane Center, Miami, Fla. said that Sub-Tropical Storm Arani is not currently as well developed as Tropical Storm Catarina was in the Southern Atlantic in 2004 or System 90Q last year.

The Brazilian Navy has marine forecasting responsibility for that part of the Atlantic designated the system a subtropical cyclone. For updates from the Brazilian Navy on Sub-Tropical Storm Arani, visit: https://www.mar.mil.br/dhn/chm/meteo/indexing.htm. NASA's Hurricane page is managed out of NASA's Goddard Space Flight Center in Greenbelt, Md.

Sub-Tropical Storm Arani is forecast to continue moving away from the Brazilian coast over the next couple of days.

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