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Hurricane Season 2009: Kirrily (Southern Indian Ocean)
April 29, 2009

Kirrily winding down Credit: NASA / MODIS Rapid Response Team
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Kirrily Wearily Winding Down

The wind shear and the cooler waters temperatures that Kirrily encountered yesterday, April 28, were too much for the storm to handle. Kirrily has now weakened to a remnant low pressure system in the northwest Arafura Sea and is expected to fade.

On April 29, Kirrily's maximum sustained winds were down to 20 knots (23 mph), which is 14 mph below the threshold for being considered a tropical storm. The Joint Typhoon Warning Center issued their final warning on Kirrily late on April 28 around 21:00 Zulu Time (5 p.m. EDT). AT that time Kirrily was near 5.4 degrees south latitude and 132.9 degrees east longitude. That's just southeast of the island of Remoon, Indonesia and about 450 miles north-northwest of Darwin, Australia. It was moving northward near 3 mph.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’s Aqua satellite captured this image Kirrily on April 28 at 1:00 a.m. EDT (05:00 UTC) when it was still a tropical storm with winds near 40 mph.

Observations of Kirrily late in the day on April 28 from the city of Tual, Kepulauan Kai indicated an even weaker system with sustained winds no greater than 10 knots (11 mph). The Kai islands are a group of islands in the southeastern Moluccas. The South Moluccas consist of about 150 islands in the Banda Sea. The Kai group forms part of Maluku province, Indonesia.

Although it isn't expected to reorganize and strengthen, forecasters at the Joint Typhoon Warning Center will still keep their eyes on Kirrily's remnants.

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

April 28, 2009

AIRS Kirrily Visible NASA's Aqua satellite captured this visible image with the AIRS instrument.
Credit: NASA JPL, Ed Olsen
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Wind Shear Weakening Cyclone Kirrily

There are two things that tropical cyclones don't like: cool sea surface temperatures and wind shear because both weaken them. It's the latter that Cyclone Kirrily is now dealing with as it works its way around the Southern Indian Ocean north of Australia.

Wind shear means that winds at different heights in the atmosphere are strong, and may be blowing from different directions weakening the storm. Wind shear has brought Kirrily's sustained winds down to 35 knots (40 mph).

On Tuesday, April 28, at 09:00 Zulu Time (5 a.m. EDT) Kirrily was quasi-stationary. It was located near 6.0 degrees south latitude and 132.9 east longitude, or about 410 nautical miles north-northeast of Darwin, Australia. It is currently affecting Indonesia's South Moluccas, which consist of about 150 islands in the Banda Sea. The islands are a part of the Republic of Indonesia. In addition to high waves in the Banda Sea, nine to ten foot high waves are also expected in the Arafuru Sea, located southeast of the Banda Sea. Kirrily is currently situated near the "border" of the Banda and Arafuru seas.

The Joint Typhoon Warning Center noted that multi-spectral satellite images shows "Deep disorganized convection over its low level circulation center," meaning that the storm is waning. However, forecasters expect the intensity to remain unchanged in the next 24 hours before Kirrily moves into a better environment with less wind shear and warmer sea surface temperatures. Once there, it can strengthen again.

AIRS Kirrily Infrared The infrared image shows that Kirrily is disorganized and not rounded anymore. Credit: NASA JPL, Ed Olsen
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NASA's Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured a visible and infrared image of Kirrily on April 28 at 4:59 UTC (1:59 a.m. EDT). In the infrared image, Kirrily appears as the somewhat rounded area in blue and purple located in the bottom right corner.

In the infrared image the orange temperatures (sea surface and land temperatures) are 80F (300 degrees Kelvin) or warmer. The storm's lowest temperatures (in purple) are associated with high, cold cloud tops. Those temperatures are as cold as or colder than 220 degrees Kelvin or minus 63 degrees Fahrenheit (F). The blue areas are around 240 degrees Kelvin, or minus 27F.

As the week progresses Kirrily is expected to take a west-southwest track toward the Timor Sea. The Timor Sea is located to the west of the Arafuru Sea, and south of the Banda Sea, separated by the island of Timor. All of these areas are expecting high seas and downpours.

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

April 27, 2009

NASA's Aqua Satellite Grabs a Cloudy, Wet Look at Indonesia's New Cyclone

Aqua image of Kirrily Credit: NRL/NASA
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Kirrily is the latest tropical cyclone to develop in the Southern Indian Ocean and two instruments on NASA's Aqua satellite grabbed data on its cold clouds and rainfall as it became a tropical storm.

Kirrily formed during the early morning hours on April 27 Zulu Time. It formed between northern Australia and south of the island of New Guinea.

Tropical cyclone Kirrily had maximum sustained winds near 40 knots (46 mph) and was moving northwest near 6 mph on April 27 at 0900 Zulu Time (5 a.m. EDT). It was located near 6.4 degrees south latitude and 134.0 east longitude, which is about 410 miles north-northeast of Darwin, Australia or due south of West Papua, the western end of the island of Papua New Guinea, located in Indonesia.

The U.S. Navy's Joint Typhoon Warning Center (JTWC) noted that "Kirrily passed over the Aru Islands and will veer west then southwest whilst gradually strengthening after 24 hours." Kirrily is generating 9 foot high waves and tropical storm force winds extend as far as 25 miles from its center.

Warnings have been posted in parts of Indonesia already. Gale-force winds and high waves "can occur in the Tanimbar Islands, Aru and Kai in 24 hours," according to JTWC. "Heavy rain may occur in the Tanimbar Islands, Aru and Kai for a few days, as well as potential flooding."

Multi-spectral satellite imagery shows that the storm is consolidating and strengthening. However, because of its close proximity and interaction with the Aru Islands, it will weaken slightly before regaining strength when it moves back into open waters in a day.

NASA's AMSR-E Instrument Sees Rainfall and More

NASA's Aqua satellite passed over Kirrily on April 28 at 04:16 Zulu Time (12:14 a.m. EDT) and captured this image with its Advanced Microwave Scanning Radiometer-E (AMSR-E) instrument. AMSR-E measured the rainfall on the eastern side of the storm (in blue, green and yellow) as being between 0.2 to 0.6 inches/hour (blue and green).

Data from AMSR-E provides measurements of precipitation rate, cloud water, water vapor, sea surface winds, and sea surface temperature, all of which are indicators in whether a tropical cyclone is strengthening or weakening. One unique aspect of AMSR-E sea surface temperature data is that it reads those surface temperatures through most types of cloud cover, supplementing infrared-based measurements that are restricted to cloud-free areas.

AIRS image of Kirrily Credit: NASA/JPL, Ed Olsen
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NASA's AIRS Instrument Sees Kirrily's Cold Clouds

The Atmospheric Infrared Sounder (AIRS), another instrument on NASA's Aqua satellite, captured Kirrily's cloud temperatures. As with the AMSR-E image, the AIRS instrument only captured the clouds on the eastern side of the storm, because the satellite's orbit was east of the storm's center.

The AIRS infrared image shows those frigid cloud top temperatures that give forecasters a clue to a storm's strength. The coldest temperatures (and highest cloud tops) are usually shown in purple. Those purple areas are as cold as 220 degrees Kelvin or minus 63 degrees Fahrenheit (F) or colder. The lower clouds are depicted as blue areas, which are around 240 degrees Kelvin, or minus 27F.

Kirrily is expected to move in a counter-clockwise motion at sea over the next couple of days.

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