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Hurricane Season 2011: Tropical Cyclone Bune (Southern Pacific Ocean)
03.29.11
 
Cyclone Bune's clouds captured from MODIS on March 27 at 02:10 UTC when it was a cyclone south of Fiji. › View larger image
This image of Cyclone Bune's clouds was captured from the MODIS instrument on NASA's Aqua satellite on March 27 at 02:10 UTC when it was a cyclone south of Fiji
Credit: NASA Goddard/MODIS Rapid Response Team
NASA Sees Extra-Tropical Cyclone Bune Fading in Southern Pacific

Bune is now an extra-tropical cyclone in the Southern Pacific Ocean far to the northeast of northern New Zealand. NASA infrared data is showing weaker thunderstorms and waning convection, indicating that Bune is on its way into history. According to the New Zealand Meteorological Service, extra-tropical Cyclone Bune is expected to stay to the northeast of Gisborne on March 30 and will then move away toward the southeast on March 31. Rains that are forecast for Gisborne on March 30 will be from southerly wind flow and not associated with extra-tropical cyclone Bune.

NASA's Aqua satellite flew over Bune on Sunday, March 27 when it was still a weak category one cyclone with maximum sustained winds near 74 mph (119 kmh/64 knots). The image still showed that Bune had an eye at that time. Animated satellite infrared imagery today, March 29, taken from the Atmospheric Infrared Sounder (AIRS) instrument that also flies aboard the Aqua satellite showed that the cloud tops of the thunderstorms were warming quickly and convection was dissipating. Warming cloud tops indicate that the thunderstorms are falling in height, and the lower the thunderstorms, the less powerful the uplift behind them is, and the weaker they are.

The last official bulletin on Bune was issued from the Joint Typhoon Warning Center on March 28 at 2100 UTC (5 p.m. EDT). At that time, Bune still had maximum sustained winds near 57 mph (92 kmh/50 knots). It was about 600 miles (965 km) northeast of Napier, New Zealand near 31.0 South latitude and 176.3 West longitude.

Today, the upper level clouds from Bune are becoming absorbed into the mid-latitude flow. That means that Bune's remnants will not be around more than a day or two.

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



March 28, 2011

AIRS captured imagery of Bune on March 25, 26, and 27 as it churned in the South Pacific Ocean. › View larger image
On March 25, Tropical Cyclone Bune was about 340 miles southeast of Nadi, Fiji and had strong thunderstorms (purple) surrounding its tightly wound center. By March 26 and on March 27, Bune's maximum sustained winds weakened to just over tropical storm status and thunderstorm development was being suppressed on its western side. On March 28, Bune's circulation weakened further as it was located about 629 miles northeast of Auckland, New Zealand.
Credit: NASA/JPL, Ed Olsen
3-Day Collage of NASA Satellite Imagery Reveals Cyclone Bune Weakening

Three days of infrared imagery from NASA's Aqua satellite showed forecasters that Cyclone Bune had weakened from a Category one cyclone to a tropical storm.

The Atmospheric Infrared Sounder (AIRS) instrument that flies aboard NASA's Aqua satellite captured imagery on March 25, 26 and 27 as Aqua flew over the storm as it churned in the South Pacific Ocean.

On March 25, Tropical Cyclone Bune was about 340 miles southeast of Nadi, Fiji and had maximum sustained winds near 75 knots (86 mph/139 kmh). AIRS imagery revealed a tight circulation and a center surrounded by high, strong thunderstorms where cloud top temperatures were as cold as or colder than the threshold of -63 F/-52C.

By March 26, Bune's maximum sustained winds weakened to 65 knots (74 mph/120 kmh), and was barely a cyclone. It had moved only 5 miles (8 km) in 24 hours to a position just 345 miles (555 km) south-southeast of Nadi, Fiji. AIRS data showed an opening in the western side of circulation where there was no thunderstorm development, and all of the strongest convection (rapidly rising air that forms the thunderstorms that power a tropical cyclone) were located mostly east of the center.

On Sunday, March 27 Bune had still maintained 65 knot (74 mph/120 kmh) maximum sustained winds at 1305 UTC (9:05 a.m. EDT) but was moving again and at that time had moved to a position some 430 miles (692 km) south of Nadi, Fiji. AIRS infrared imagery revealed that the area on the western side where there were no thunderstorms had grown, and that the circulation was no longer tightly wound. Most of the strongest convection were outside of the center of circulation from north to south, on the eastern side of the storm.

By Monday, March 28, Bune weakened further and had maximum sustained winds near 50 knots (57 mph/92 kmh). On the 28th Bune was located about 629 miles (1012 km) northeast of Auckland, New Zealand and was moving at 15 knots (17 mph/27 kmh) toward the southeast. AIRS data still showed that the strongest convection was south and east of Bune's center of circulation and dry air is wrapping around the western and northern parts of the storm, which is why the thunderstorms are unable to develop in those quadrants of the storm.

Bune is now undergoing extra-tropical transitioning as it moves southeast. The system is forecast to become totally extra-tropical by Tuesday, March 29 as it continues moving into cooler waters and an area of increased wind shear.

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



TRMM's analysis of rainfall within Tropical Cyclone Bune on March 24 showed bands of thunderstorms with heavy rainfall. › View larger image
TRMM's analysis of rainfall within Tropical Cyclone Bune on March 24 showed bands of thunderstorms with heavy rainfall (red), falling at about 2 inches (50 mm) per hour. Other areas of light to moderate rainfall were occurring at rates between .78 to 1.57 inches (20 and 40 mm) hour.
Credit:
NASA's TRMM Satellite Sees Intense Thunderstorms in Cyclone Bune

Cyclone Bune may have been at sea in the South Pacific Ocean on Thursday, March 24 but NASA's Tropical Rainfall Measuring Mission (TRMM) satellite noticed some strong thunderstorms were occurring around its center of circulation.

Tropical cyclone Bune was southeast of the Fiji Islands and close to a category one on the Saffir-Simpson scale when the TRMM satellite passed above on March 24, 2011 at 1548 UTC (11:48 EDT). Two instruments aboard the satellite, called the TRMM Microwave Imager (TMI) and Precipitation Radar (PR) provided data to the TRMM science team at NASA's Goddard Space Flight Center in Greenbelt, Md. to create an image of the rainfall happening in the storm. The satellite overpass showed that large rain bands around Bune contained numerous intense thunderstorms. Rainfall rates within those bands of thunderstorms were falling at about 2 inches (50 mm) per hour.

Text Credit: Hal Pierce, SSAI/NASA





March 25, 2011

GOES image of Tropical Storm Bune› View larger image
The GOES-11 satellite captured an infrared image of Cyclone Bune on March 25, 2011 at 1500 UTC as it moves through the Southern Pacific Ocean. The black area to the left is space as the image shows the curvature of the Earth. Credit: NOAA/NASA GOES Project
GOES-11 Satellite Sees Bune Strengthen to a Cyclone

Tropical Storm Bune strengthened into a Cyclone on March 25 and the GOES-11 satellite captured a stunning infrared view of it from space.

The Geostationary Operational Environmental Satellite called GOES-11 is in a geostationary orbit and provides weather imagery for the western U.S. but its view reaches into the western and southern Pacific Ocean. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers. The infrared image the GOES-11 satellite captured on March 25 at 1500 UTC (11 a.m. EDT) showed a well-organized Tropical Cyclone Bune moving through the southern Pacific Ocean.

GOES satellites are operated by the National Oceanic and Atmospheric Administration, and images and animations of GOES data are created by NASA's GOES Project, located at NASA's Goddard Space Flight Center, Greenbelt, Md.

At 0600 UTC (2 a.m. EDT) on March 25, Cyclone Bune had maximum sustained winds near 75 knots (86 mph/138 kmh). It was located about 340 nautical miles southeast of Nadi, Fiji near 22.5 South latitude and 179.2 West longitude. It was moving toward the south-southeast near 5 knots (6 mph/9 kmh) and toward northeastern New Zealand.

Infrared satellite imagery, such as that from the Atmospheric Infrared Sounder (AIRS) that flies on NASA's Aqua satellite showed that there is strong convective (rapidly rising air forming thunderstorms) banding (bands of thunderstorms) west of the center of Bune's circulation. However, those bands of thunderstorms are fragmented. To the east of the center, the bands of thunderstorms appear more organized. There's even a small eye in the center of Bune.

Because a subtropical ridge (elongated area) of high pressure is building to the southwest of Cyclone Bune, it is expected to steer the storm in a more south-southwesterly direction over the weekend. After the weekend, Bune is forecast to move to the southeast. Forecasters at the Joint Typhoon Warning Center expect Bune to weaken after 72 hours because of increasing wind shear and cooler sea surface temperatures and should become extratropical next week northeast of New Zealand.

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



March 24, 2011

AIRS image of Tropical Storm Bune› View larger image
Aqua's Atmospheric Infrared Sounder (AIRS) instrument captured Bune's (purple and blue) high thunderstorm cloud temperatures at 1:35 UTC on March 24, 2011. The strongest thunderstorms were north of the center of circulation (purple). Credit: NASA JPL, Ed Olsen
NASA Satellite Attends the Birth of Tropical Storm Bune in Southern Pacific

It's not unusual for NASA satellites to attend the birth of tropical cyclones, and NASA's Aqua satellite was there when Tropical Cyclone Bune was born early today in the South Pacific Ocean.

Bune developed from System 99P, a low pressure area that was about 200 miles southeast of Suva, Fiji yesterday, March 23. The low intensified into tropical depression 19P and today strengthened further into Tropical Storm Bune.

A Tropical Cyclone Alert is in force for Lau, Lomaiviti and nearby smaller islands. A strong wind warning is also in force for the Lau group, Lomaiviti group and nearby smaller islands.

NASA's Aqua satellite captured an infrared image of Bune that showed strongest convection (rapidly rising air that forms the thunderstorms that make up a tropical cyclone) was occurring on the north side of the center of circulation. That's where the cloud top temperatures were the coldest, and the thunderstorms were the highest, and strongest. The low-level circulation center also appears to be consolidating (strengthening) on infrared imagery.

Infrared imagery measures temperatures and not only can it see cold, high cloud tops in tropical cyclones, but also the warm ocean waters that power the cyclones (if the sea surface temperatures are over 80F (26.6 C)). Cold cloud top temperatures provide clues about the power of the thunderstorms in a tropical cyclone. The colder the clouds are, the higher they are, and the more powerful the thunderstorms are that make up the cyclone. Bune's cloud temperatures were colder than - 63F (-52C), indicating very cold, high, strong thunderstorms within.

Today, March 25 at 0900 UTC (5 a.m. EDT), Tropical Storm Bune's maximum sustained winds were up to 45 knots (52 mph/83 kmh) with higher gusts. It was moving away from Fiji and is now located about 260 miles (418 km) southeast of Suva, Fiji near 21.1 South latitude and 179.8 West longitude. Tropical-Storm force winds extended outward from the center up to 50 miles (80 km). It was creating 15 foot (4.5 meter) high waves.

Forecasters at the Joint Typhoon Warning Center are forecasting intensification as the storm moves away from Fiji. It is expected to become extra-tropical far to the north of New Zealand.

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