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Hurricane Season 2009: System 97W (Western Pacific)
12.04.09
 
December 4, 2009

TRMM's analysis of rainfall within System 97W on Dec. 3 showed a very limited area of moderate rainfall. > View larger image
TRMM's analysis of rainfall within System 97W on Dec. 3 showed a very limited area of moderate rainfall. The yellow and green areas indicate rainfall between .78 to 1.57 inches per hour.
Credit: NASA/SSAI, Hal Pierce
The end of Nida (top left) and System 97W already beginning to fade (lower right) as it appears stretched out. > View larger image
This NASA Aqua satellite infrared image Dec. 3 at 1653 UTC showed the end of Nida (top left) and System 97W already beginning to fade (lower right) as it appears stretched out.
Credit: NASA JPL, Ed Olsen
System 97W's "Castle Wall" Breached, and Opened Up to Dissipation

The "walls" of System 97W have been breached, and residents in the Western Pacific Ocean no longer have a tropical cyclone to worry about today. The Joint Typhoon Warning Center cancelled their "formation alert" for System 97W. System 97W is following in Nida's footsteps and is headed for dissipation. Nida has now officially dissipated.

Animated infrared satellite imagery from early today, December 4, showed that the same thing that happened with Nida has happened with System 97W: its low-level circulation center is now exposed. That means that outside influences like wind shear and dry air can work their way into System 97W's center and weaken it from the inside out.

Think of a tropical cyclone's center of circulation like a castle wall. Once it is breached, anything from the outside can enter and take over or destroy whatever is inside.

System 97W's open center is near 17.3 North latitude and 141.0 East longitude, about 310 nautical miles northwest of Guam. Satellite data shows that the deepest convection (strongest thunderstorm activity) is to the north and northwest of the center, pushed there from wind shear.

The Tropical Rainfall Measuring Mission (TRMM) Satellite, managed by NASA and the Japanese Space Agency flew over System 97W at 15:35 UTC yesterday (10:35 a.m. ET). At that time TRMM's data noticed that the low-level center of circulation was already becoming elongated (an indication that wind shear is stretching the storm, and skewing circulation), and the heavier rains were located from 60 to 120 nautical miles northwest of the storm's center.

The Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured an infrared image of 97W on Dec. 3 at 1653 UTC that showed System 97W was already elongated.

Not only is System 97W getting weakened from an open "wall" but it's also moving into an area where the wind shear is higher. The vertical wind shear speeds are between 25 and 35 knots (28-40 mph) from the south. Not only that, but there's a cold front approaching, too.

System 97W is expected to track to the north and fizzle as it encounters that cold front and high wind shear.

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



December 3, 2009

Tropical Depression Nida (top left) on December 3 at 1:35 UTC and System 97W (bottom right). > View larger image
The MODIS instrument on NASA's Terra satellite captured an image of Tropical Depression Nida (top left) on December 3 at 1:35 UTC and System 97W (bottom right).
Credit: NASA MODIS Rapid Response
Nida fading top left (in purple and blue) on Dec. 2 at 16:11 UTC (11:11 a.m. ET) and System 97W developing (bottom right). > View larger image
This infrared image from AIRS shows Nida fading top left (in purple and blue) on Dec. 2 at 16:11 UTC (11:11 a.m. ET) and System 97W developing (bottom right). The highest, coldest, thunderstorm cloud tops are in purple (as cold as -63F).
Credit: NASA JPL, Ed Olsen
NASA's Terra and Aqua Satellites See Nida Fading, and 97W Getting Organized

NASA's Terra and Aqua satellites flew over Tropical Depression Nida and System 97W in the Western Pacific Ocean and noticed that one is fading while the other is powering up.

The Moderate Imaging Spectroradiometer or MODIS instrument that flies on NASA's Terra satellite captured a visible image of the two storms in one satellite pass. Nida still had a swirl to its clouds although the system has continued to weaken. On the visible imagery, System 97W currently appears as a rounded area of clouds with no established center.

The Atmospheric Infrared Sounder or AIRS instrument captured an infrared snapshot of both storm's cold cloud tops in one image. That provided more detail about the storms, showing Nida as elongated from southwest to northeast, indicating that the storm is coming apart. The infrared imagery also showed System 97W as a rounded area, indicating a strengthening circulation.

On December 3 at 0300 UTC, the Joint Typhoon Warning Center issued its final advisory on Tropical Depression Nida. Nida had maximum sustained winds down to 28 mph (25 knots), and was still crawling along at 4 mph to the northwest. It was located about 450 miles southeast of Kadena, near 21.6 North latitude and 134.2 East longitude.

Animated multispectral satellite imagery indicated that the low level circulation center, the storm's core, was fully exposed, and didn't show any strong convection. Convection is important because it's rapidly rising air that promotes the development of thunderstorms that power a tropical cyclone. It's like a car without gasoline, it's not going anywhere. Another thing that's leading to Nida's demise is cool, dry air moving into the edges of the storm. Because of dry air, wind shear and an open center, Nida is expected to last only another 24 hours.

As Nida fades, System 97W is getting organized. Earlier today, December 3, System 97W's center was located about 110 nautical miles west of Guam, near 13.6 North latitude and 142.9 East longitude. Currently, its maximum sustained winds are around 28 mph, and it is moving away from Guam in a west-northwesterly direction near 10 mph. Current estimated minimum central pressure from the system is around 1002 millibars. The storm is also moving into a better atmospheric environment, which will allow it to strengthen.

The Joint Typhoon Warning Center noted that the "Likelihood of tropical cyclone formation is good."

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



December 2, 2009

This NASA infrared AIRS satellite image shows Nidastill has some stronger thunderstorms around its center. > View larger image
This NASA infrared AIRS satellite image shows Nida (top left) still has some stronger thunderstorms around its center (higher, stronger storms are depicted in purple). Meanwhile System 97W (bottom right) is also showing some strong thunderstorms in the southeastern side (purple).
Credit: NASA JPL, Ed Olsen
This NASA visible AIRS satellite image shows Nida (top left) looking elongated, almost like a cocoon. > View larger image
This NASA visible AIRS satellite image shows Nida (top left) looking elongated, almost like a cocoon.
Credit: NASA JPL, Ed Olsen
Nida Getting Knocked By Winds, and 97W Piquing Interest

Nida is now a tropical storm, and is being knocked around by wind shear in the Western Pacific. Satellite imagery has confirmed Nida's center of circulation is exposed and the storm is losing its circular shape. Meanwhile, System 97W located to Nida's southeast looks ominous on NASA satellite imagery.

Tropical Storm Nida's winds are around 57 mph (50 knots) today, December 2. Nida is moving west-northwest near 9 mph. At 10 a.m. ET, Nida was located about 505 nautical miles southeast of the island of Kadena, near 21.3 North and 134.8 East.

Kadena is a United States Air Force (USAF) base located in the towns of Kadena and Chatan and the city of Okinawa, in Okinawa Prefecture, Japan. Kadena Air Base is the hub of U.S. airpower in the Pacific, and home to the USAF's 18th Wing and a variety of associate units.

NASA satellite data has helped forecasters see that the storm is elongating. Visible data from NASA's Aqua satellite, using the Atmospheric Infrared Sounder (AIRS) instrument showed the storm stretching in a northeast to southwest direction.

In addition, the Joint Typhoon Warning Center (JTWC) noted "Animated multispectral satellite imagery showed a fully exposed low level circulation center (LLCC) nearly one degree to the southwest of increasingly sheared convection." The convection (thunderstorms) near the LLCC is making the center difficult to locate on satellite imagery. The JWTC also notes that "the latest microwave imagery (like that from AIRS and NASA's Advanced Microwave Sounding Unit (AMSU) instruments both on NASA's Aqua satellite) indicates a weakened low level signature as well."

The AMSU instrument on NASA's Aqua satellite also showed that Nida's warm core has contracted and has become increasingly asymmetric. In addition, the core has dropped several thousand feet into the mid to lower troposphere. That's an indication of a weakening storm.

Because wind shear has increased to over 34 mph (30 knots), Lida isn't expected to continue weakening and dissipate over open water in the next three days. In addition, Lida is no longer expected to swing north and track to the west of Iwo To, but will likely keep zigzagging to the west-northwest until it fades.

System 97W, however, looks interesting on NASA satellite imagery. In the latest AIRS imagery 97W can be seen to the east of Tropical Storm Nida. It is centered about 235 miles southeast of Guam, near 10.4 North and 147.1 East. The JTWC has upgraded the likelihood of tropical cyclone formation for this system to "fair."

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