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Hurricane Season 2009: Tropical Storm Bongani (Southern Indian Ocean)
11.27.09
 
November 27, 2009

NASA's Aqua satellite captured cold thunderstorm cloud tops of Bongani in this infrared image of Nov. 25. > View larger image
NASA's Aqua satellite captured cold thunderstorm cloud tops of Bongani in this infrared image of Nov. 25 at 5:25 a.m. ET, and showed the storm elongating over northern Madagascar.
Credit: NASA JPL, Ed Olsen
NASA's Aqua satellite captured this visible image of Bongani on Nov. 25. > View larger image
NASA's Aqua satellite captured this visible image of Bongani on Nov. 25. Central and southern Madagascar are clearly visible, while the northern end of the island is obscured by Bongani's clouds.
Credit: NASA JPL, Ed Olsen
Bongani Dissipated in Mozambique Channel

Tropical Cyclone Bongani dissipated today, November 26, in the Mozambique Channel as a result of wind shear.

Wind shear is a difference in wind speed and direction over a relatively short distance in the atmosphere. Wind shear can be both vertical and horizontal. Horizontal wind shear is seen across front, while vertical wind shear can be near the Earth's surface or higher levels in the atmosphere near upper level jet streams. Wind shear can tear storms apart. If you think of a tropical cyclone as a haystack, and you direct giant fans blowing at different heights of the stack, going different ways, that's similar to how wind shear affects a tropical cyclone. It pushes into its circulation, weakening it.

The last fixed location for Bongani was on November 25 at 2100 UTC (4 p.m. ET or 11 p.m. local Africa/Maputo time. Bongani's center was in the Mozambique Channel near 12.0 degrees South latitude and 47.8 East longitude. Its maximum sustained winds were down to 23 mph (20 knots) at that time.

Bongani dissipated in the Mozambique Channel, just west of northern Madagascar.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center














November 25, 2009

NASA's Aqua satellite captured cold thunderstorm cloud tops of Bongani in this infrared image of Nov. 25. > View larger image
NASA's Aqua satellite captured cold thunderstorm cloud tops of Bongani in this infrared image of Nov. 25 at 5:25 a.m. ET, and showed the storm elongating over northern Madagascar.
Credit: NASA JPL, Ed Olsen
NASA's Aqua satellite captured this visible image of Bongani on Nov. 25. > View larger image
NASA's Aqua satellite captured this visible image of Bongani on Nov. 25. Central and southern Madagascar are clearly visible, while the northern end of the island is obscured by Bongani's clouds.
Credit: NASA JPL, Ed Olsen
NASA's Aqua Satellite Sees Tropical Storm Bongani Approaching Mozambique Channel

NASA's Aqua satellite flew over Cyclone Bongani today and provided some important data that have helped forecasters figure out where the storm is headed, and helped them see that it has changed course.

The Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured infrared, microwave and visible images of Tropical Cyclone Bongani, and provided data on cloud height and extent, cloud top temperatures, and pressure. The infrared imagery also showed that Bongani has elongated over the northern tip of Madagascar, indicating that its interaction with the land has weakened the storm.

High thunderstorm cloud tops indicate a strong storm. When the thunderstorm cloud heights start dropping, they become less cold, and the thunderstorms are less powerful. Cloud-top temperatures are important because they tell forecasters how high thunderstorms are, and the higher the thunderstorm, the colder the cloud tops and the more powerful the thunderstorms. Today's (November 25) AIRS images showed high, cold, thunderstorm cloud tops as cold as -63F. Those thunderstorms were dropping heavy rainfall.

On November 25, Bongani had maximum sustained winds near 42 mph, with higher gusts. Its center was located about 480 miles north-northeast of Antananarivo, Madagascar, near 11.6 degrees South latitude and 50.2 East longitude. Bongani was moving west-southwest near 9 mph and generating waves 12 feet high at the entrance of the Mozambique Channel.

After Bongani passes Madagascar and emerges fully into the Mozambique Channel, it is expected to re-intensify briefly before weakening.

Bongani is now forecast to head south through the Mozambique Channel and parallel the coast of Madagascar over the next 5 days.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center



November 24, 2009

Bongani has some stronger thunderstorms around its center (higher, stronger storms are depicted in purple). > View larger image
This NASA infrared AIRS satellite image shows Bongani has some stronger thunderstorms around its center (higher, stronger storms are depicted in purple) on November 23 at 5:35 a.m. ET.
Credit: NASA JPL, Ed Olsen
NASA Spots Tropical Storm Bongani, Second of the Southern Indian Ocean Season

NASA satellites have been flying over the Tropical Storm Bongani in the Southern Indian Ocean, capturing rainfall, cloud temperature, cloud heights and more. Bongani is the second tropical cyclone in the southern hemisphere season and is already poised for a landfall in Mozambique later this week.

At 4 a.m. ET (0900 UTC) on November 24, Bongani was located 560 miles north-northeast of Antananarivo, Madagascar, near 10.9 degrees south latitude and 51.9 east longitude. Bongani had maximum sustained winds near 46 mph (40 knots), and was moving south-southwest near 13 mph (11 knots) toward the northern cape of Madagascar, into the northern section of the Mozambique Channel. It's generating waves of 13 feet in the Southern Indian Ocean.

NASA's Aqua satellite captured the high, cold thunderstorm tops that lie mostly to the northeast of the center of circulation. Those high thunderstorms indicate strong convection (rapidly rising air that forms the thunderstorms that make up a tropical cyclone) and are a sign that the storm will continue to intensify. Adverse atmospheric conditions, however await Bongani, and those conditions will weaken the storm after brief time of intensification.

Bongani is forecast to skirt the northernmost point of Madagascar, continue heading south-southwest and make landfall in Mozambique on Friday.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center