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Hurricane Season 2011: Cyclone Alenga (Southern Indian Ocean)
12.09.11
 
This TRMM 3-D image revealed powerful towering thunderstorms near the Alenga's center. › View larger image
This TRMM 3-D image, created from data on Dec. 8 at 1005 UTC (5:05 a.m. EST) revealed powerful towering thunderstorms near the Alenga's center were pushing up to heights of over 16 km (~9.9 miles). The towers were not visible on Dec. 9 after the storm weakened.
Credit:
TRMM provided a › View larger image
TRMM provided a "top down" rainfall analysis of Tropical Storm 02S on Dec. 8 at 1005 UTC (5:05 a.m. EST). Light to moderate rainfall (green and blue) was falling mostly east of the center at a rate between .78 to 1.57 inches/20 to 40 mm per hour). There was a small area of heavy (red) rainfall to the east of the center.
Credit: NASA/SSAI, Hal Pierce
TRMM Sees Powerful Tropical Cyclone Alenga Before It Weakened Quickly

Yesterday, Tropical Cyclone Alenga's wind speeds increased to a maximum of about 90kts (~104 mph) and today and NASA's TRMM satellite saw some powerful towering thunderstorms within. Early today, Alenga was barely a tropical storm and most of its power has faded after being battered by dry air, wind shear and cooler waters.

Alenga was at maximum intensity when NASA's Tropical Rainfall Measuring Mission or TRMM satellite passed directly above in the early evening of December 8, 2011 at 1005 UTC. A precipitation analysis from TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) were overlaid on a Visible/Infrared image from Visible and InfraRed Scanner (VIRS) data. This analysis showed that very heavy rainfall of over 50 mm/hr (~2 inches) was being produced by intense storms in the Alenga's eye wall at that time.

TRMM data was used to create a 3-D vertical slice through Alenga. TRMM's radar was able to see through Alenga's cloud cover and reveal that very powerful storms in the center of the tropical cyclone had strong radar reflectivity values of over 53 dBZ.

By December 9 at 0900 UTC (4 a.m. EST), Alenga's maximum sustained winds had fallen by more than 60 mph to 40 mph (35 knots). It was located about 640 nautical miles west of Learmonth, Australia near 21.6 South and 102.7 East. The low level center is now fully exposed to outside winds and is deteriorating quickly. Wind shear from the northwest has pushed most of the thunderstorms associated with Alenga some 200 nautical miles to the southeast of the center. Alenga is forecast to dissipate by Saturday, Dec. 10.

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












Dec. 8, 2011

MODIS captured a visible image of Cyclone Alenga when it passed overhead on Dec. 8 at 7:10 UTC (2:10 a.m. EST). › View larger image
On Dec. 8 at 7:10 UTC (2:10 a.m. EST), the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA's Aqua satellite captured a visible image of Cyclone Alenga when it passed overhead from space. Alenga appeared as a rounded area of compact clouds.
Credit: NASA Goddard MODIS Rapid Response Team
NASA Sees Alenga Become a Cyclone in the Southern Indian Ocean

NASA's Aqua satellite passed over Cyclone Alenga and captured a visible image of the rounded and more powerful storm is it makes its way toward Western Australia.

Alenga had grown from a tropical storm to a cyclone by 0300 UTC on Dec. 8 (10 p.m. EST, Dec. 7) when its maximum sustained winds reached 90 knots (103 mph/166 kmh).

On Dec. 8 at 7:10 UTC (2:10 a.m. EST), the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA's Aqua satellite captured a visible image of Cyclone Alenga when it passed overhead from space. Alenga appeared as a rounded area of compact clouds. Although an eye was not apparent on visible imagery, it was seen in earlier infrared imagery. At that time, Alenga's winds had decreased as a result of wind shear.

By 1500 UTC (10 a.m. EST) on Dec. 8, Alenga's maximum sustained winds were down to 80 knots (92 mph/148 kmh). Cyclone-force winds extended 25 miles (40 km) out from the center of the storm, while tropical storm-force winds extended out to 110 miles (177 km), making the storm at least 220 miles (354 km) in diameter. Alenga was about 400 nautical miles (460 miles/740 km) south-southeast of the Cocos Islands, near 18.9 South latitude and 99.6 East longitude. It was speeding to the east-southeast near 22 knots (25 mph/40 kmh). Infrared imagery at 1500 UTC no longer showed an eye, further indication that the storm was weakening.

In addition to facing higher wind shear, a field of cold air stratocumulus clouds to the west is moving into the low level circulation of the center, and cold air also weakens tropical cyclones. Alenga is also being stretched out from the wind shear, and the strongest convection (rising air that forms the thunderstorms that make up the tropical cyclone) is now starting to stretch to the southeast of the storm's center. Alenga now faces even a third challenge: dry air. Dry air is also starting to affect the western side of the storm by absorbing moisture and eroding the band of thunderstorms.

The Joint Typhoon Warning Center expects Alenga to begin transitioning to an extra-tropical storm later today. As it begins that transition, however, the cold and dry air and the increased wind shear will work in tandem with the cooler sea surface temperatures that lay ahead in Alenga's path to cause the storm to weaken quickly.

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



Dec. 7, 2011

TRMM's 3-D image revealed powerful thunderstorms in Alenga pushing up to heights of over 16 km (~9.9 miles). › View larger image
This TRMM 3-D image revealed powerful towering thunderstorms near the Alenga's center were pushing up to heights of over 16 km (~9.9 miles). The release of energy within these tall towers are often a sign that a storm is intensifying.
Credit: NASA/SSAI, Hal Pierce
TRMM provided a › View larger image
TRMM provided a "top down" rainfall analysis of Tropical Storm Alenga on Dec. 5 at 2103 UTC (6:03 p.m. EST). The red areas indicate heavy rainfall of 2 inches (50 mm) per hour. Light to moderate rainfall (green and blue) was falling at a rate between .78 to 1.57 inches/20 to 40 mm per hour).
Credit: NASA/SSAI, Hal Pierce
NASA Sees Tropical Storm Alenga Intensifying

NASA's TRMM satellite passed over Tropical Storm Alenga and noticed that the rainfall has intensified in the storm in the last two days indicating that it continues strengthening.

The Tropical Rainfall Measuring Mission satellite called TRMM again passed over intensifying tropical storm Alenga in the South Indian Ocean on December 5, 2011 at 2103 UTC (6:03 p.m. EST). As expected, Alenga had become better organized with TRMM's Precipitation Radar (PR) seeing scattered bands of heavy rainfall spiraling into the center of the storm.

A 3-D image using TRMM PR was created at NASA's Goddard Space Flight Center in Greenbelt, Md. Very powerful storms were seen in the 3-D image. Some of those powerful thunderstorms reached heights of about 16 km (~9.9 miles). TRMM PR also found a reflectivity value of 53.67 dBZ which is an another indication that very heavy rainfall was occurring in those storms.

On Dec. 7, 2011 at 0600 UTC (1 a.m. EST), Tropical Storm Alenga's maximum sustained winds were up to 55 knots (63 mph/102 kmh)from 45 knots (52 mph/83 kmh)a day ago. Alenga was still safely at sea and far from land. The center of Alenga was located about 415 nautical miles west-southwest of the Cocos Islands near 14.5 South latitude and 90.2 East longitude. Alenga was moving to the east-southeast near 15 knots (17 mph/28 kmh).

On Dec. 7, satellite imagery showed improved banding of thunderstorms around the low-level center of the cyclone. The strongest bands of thunderstorms were on the northern side of Alenga's center.

Tropical Storm Alenga is forecast to keep strengthening because of warm sea surface temperatures and low wind shear. Alenga may reach hurricane-force over the next day or two before encountering strong westerly wind shear and weakening.

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






Dec. 6, 2011

TRMM's 3-D image revealed a few storms near Alenga's center were pushing up to heights of over 12 km (~7.45 miles). › View larger image
TRMM's Precipitation Radar (PR) data is depicted in a 3-D image that revealed a few powerful storms near the storm's center were pushing up to heights of over 12 km (~7.45 miles).
Credit: NASA/SSAI, Hal Pierce
TRMM provided a › View larger image
TRMM provided a "top down" rainfall analysis of Tropical Storm Alenga on Dec. 4 at 12:10 UTC (7:10 a.m. EST). The red areas indicate heavy rainfall of 2 inches (50 mm) per hour. Light to moderate rainfall (green and blue) was falling at a rate between .78 to 1.57 inches/20 to 40 mm per hour).
Credit: NASA/SSAI, Hal Pierce
NASA's TRMM Satellite Sees the Power in Tropical Storm Alenga

The first tropical storm of the Southern Indian Ocean season has been renamed from Tropical Storm 01S to Tropical Storm Alenga as it continues to strengthen. NASA's TRMM satellite was able to capture a look at the rainfall rates and cloud heights within Alenga recently.

On December 4, 2011 at 1210 UTC (7:10 a.m. EST) the Tropical Rainfall Measuring Mission (TRMM) satellite had a look at the first tropical storm forming in the Indian Ocean this season. Tropical cyclones normally form in this area between November 15 and April 30 so this one was a little overdue.

The TRMM satellite is managed by both NASA and the Japanese Space Agency, and obtains rainfall measurements in the tropics. TRMM provided a "top down" rainfall analysis of Tropical Storm Alenga on Dec. 4 at 12:10 UTC (7:10 a.m. EST) using the TRMM Microwave Imager (TMI) and Precipitation Radar (PR) overlaid on an enhanced infrared image from Visible and InfraRed Scanner (VIRS) data. This analysis was done at NASA's Goddard Space Flight Center in Greenbelt, Md. and showed that very heavy rainfall of over 50 mm (~2 inches) per hour was occurring in the forming tropical cyclone near the center of its circulation.

Hal Pierce of NASA's TRMM Team at NASA Goddard made the December 4 images from TRMM Data. Pierce said, "TRMM's Precipitation Radar (PR) data is depicted in a 3-D image that revealed a few powerful storms near the storm's center were pushing up to heights of over 12 km (~7.45 miles). The release of energy within these tall towers are often a sign that a storm is intensifying."

On Dec. 6 at 4 a.m. EST (0900 UTC), Alenga's maximum sustained winds were near 45 knots (52 mph/83 kmh). Alenga was located in the Southern Indian Ocean's open waters 560 nautical miles west of the Cocos Islands, near 12.8 South latitude and 87.5 East longitude. Alenga was moving to the southwest near 2 knots (3 mph/4 kmh).

Infrared satellite imagery today, Dec. 6 showed that the showers and thunderstorms within Alenga are decreasing, and the bands of thunderstorms around its center are weakening. The Joint Typhoon Warning Center noted that this weakening is only temporary as Alenga is forecast to regain strengthen before weakening again two days from now as it becomes an extra-tropical storm.

As Alenga continues to head southeast, it is moving into a hostile environment, where wind shear will increase and batter the tropical cyclone, weakening it.

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



Dec. 5, 2011

MODIS captured an image of Tropical Cyclone 01S on Dec. 5 at 08:18 UTC (3:18 a.m. EST). › View larger image
The MODIS instrument on NASA's Aqua satellite captured an image of Tropical Cyclone 01S on Dec. 5 at 08:18 UTC (3:18 a.m. EST) in the Southern Indian Ocean. Strong thunderstorms are visible around the center as they cast shadows on the lower surrounding clouds.
Credit: NASA/NRL
NASA Sees Birth of First Southern Indian Ocean Season Tropical Storm

The Southern Indian Ocean cyclone season is off and running and NASA's Aqua satellite saw the birth of Tropical Cyclone 01S.

Tropical Cyclone 01S (TC01S) formed today December 5, 2011. TC01S has maximum sustained winds near 55 knots (63 mph/102 kmh) and is rapidly consolidating and organizing, so strengthening is forecast. At 0900 UTC (4 a.m. EST) on Dec. 5, TC01S was located about 545 nautical miles west of the Cocos Islands near 12.2 South and 87.0 East. It was moving to the west at 7 knots 8 mph/13 kmh).

The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Aqua satellite captured an image of Tropical Cyclone 01S on Dec. 5 at 08:18 UTC (3:18 a.m. EST) in the Southern Indian Ocean. Strong thunderstorms are visible around the center as they cast shadows on the lower surrounding clouds.

Microwave satellite instruments showed an eye developing in TC01S. There is also tightly curved banding of thunderstorms around the low-level center. T01S has intensified rapidly over the first 12 hours of its existence. The Joint Typhoon Warning Center forecasters expect TC01S to strengthen to hurricane-force over the next two days and track to the southeast, staying at sea.

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