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Hurricane Season 2009: Ilsa (Southern Indian Ocean)
03.25.09
 
March 25, 2009

Cyclone Ilsa No More

satellite image of Ilsa Credit: NASA JPL, Ed Olsen
> Larger image
The Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured this visible image of Ilsa on Mar. 24 at 07:41 UTC (2:41 a.m. EDT) as the satellite flew overhead.

On March 24 at 15:00 UTC (11:00 a.m. EDT), the remnants of Cyclone Ilsa were located about 365 nautical miles south-southwest of the Cocos Islands, near 18.4 south latitude and 92.0 east longitude. It has tracked west-southwest at 10 knots (11 mph). Ilsa at that time had sustained winds near 35 knots (40 mph), but it has since dissipated.

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



March 23, 2009

NASA Satellites See Cyclone Ilsa's Winds and Rains Wane

Quikscat image of Ilsa> Click for larger image
Credit: NASA/NRL
NASA's Quick Scatterometer satellite (QuikScat) can measure surface wind speeds of cyclones by using microwaves to peer into the clouds and recently caught Cyclone Ilsa's winds waning in the southern Indian Ocean. At the same time, NASA's Tropical Rainfall Measuring Mission satellite is seeing the intensity of Ilsa's rains wane, too.

QuikScat data shows wind speeds in different colors and wind direction as indicated by small barbs. The black barbs point to areas with wind speeds between 33-49 knots (38-56 mph). The two purple barbs show higher wind speeds near Ilsa's center between 50-60 knots (57-69 mph), which in this case are likely wind gusts, as the average wind speed recorded at this time was 45 knots (52 mph). This image was captured on Mar. 22 at 23:26 UTC (7:26 p.m. EDT). The minimum central pressure at the time of this image was 989 millibars. QuikScat has shown forecasters that tropical storm-force winds are occurring as much as 50 miles from the center of the storm.

Since the QuikScat satellite image was taken, Ilsa's winds slowed even more. Her sustained winds were down to 40 knots (46 mph)on Mar. 23 at 09:00 UTC (5:00 a.m. EDT). Ilsa was located about 365 miles south-southwest of the Coco Islands, near 17.5 degrees south and 94.1 degrees east at that time. She was moving west southwest near 12 knots, and will continue in the open waters. Ilsa is not a threat to any landmasses.

TRMM image of Ilsa> Click for larger image
Credit: Hal Pierce, SSAI/NASA
NASA's TRMM Satellite Analyzes Rainfall from Space

The image to the right was made from data captured by the Tropical Rainfall Measuring Mission (TRMM) satellite on Mar. 22 at 16:28 UTC (12:28 p.m. EDT). This TRMM image shows how intense the rain is falling within Ilsa. The center is located near the yellow, green and red areas, which indicate rainfall between 20 and 40 millimeters (.78 to 1.57 inches) per hour. The small red area in the center of the image is considered moderate rainfall. The image shows that most of the rainfall is considered less than "moderate" which would indicate a weakening storm. TRMM is a joint mission between NASA and the Japanese space agency JAXA.

Over the last several days, Cyclone Ilsa continued to weaken as oceanic conditions deteriorated (it is moving into cooler waters). The forecast for Ilsa calls for the system to slowly weaken and dissipate in a few days.

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


March 20, 2009

Category 3 Cyclone Ilsa Will Weaken on Weekend

AIRS image of Ilsa taken on March 19, 2009> Click for larger image
Credit: NASA JPL, Ed Olsen
Cyclone Ilsa has become a powerful Category 3 Cyclone on the Saffir-Simpson Scale (the scale that measures hurricane/cyclone intensity). Because Ilsa is going to move into cooler waters over the weekend, however, the storm is expected to weaken.

On Friday, Mar. 20, at 03:00 Zulu Time (Mar. 19 at 11 p.m. EDT), Ilsa was packing maximum sustained winds near 110 knots (126 mph). That's the upper end of the Category Three scale that ranges from 111-130 mph winds. Ilsa was located safely at sea in the Indian Ocean, about 530 miles east-southeast of the Coco Islands, near 16.6 degrees south and 104.5 degrees east. Ilsa continued moving westward near 10 knots (11 mph).

The Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured a visible and infrared image of Ilsa on Mar. 19 at 18:11 UTC (2:11 p.m. EDT).

The infrared image clearly shows a large temperature difference between Ilsa's cloud tops and the warm ocean temperatures. In this image, the orange temperatures are 80F (300 degrees Kelvin) or warmer. Ilsa'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.

AIRS generates infrared, microwave and visible images. The AIRS infrared data creates an accurate 3-D map of atmospheric temperature, water vapor and clouds, all of which are helpful to forecasters.

TRMM image of Ilsa taken on March 20, 2009> Click for larger image
Credit: NASA/SSAI, Hal Pierce
NASA's TRMM Satellite Analyzes Rainfall from Space

The image above was made from data captured by the Tropical Rainfall Measuring Mission (TRMM) satellite on Mar. 20 at 8:31 UTC (4:31 a.m. EDT). This TRMM image shows the horizontal pattern of rain intensity within Ilsa. The center is located near the yellow, green and red areas, which indicate rainfall between 20 and 40 millimeters (.78 to 1.57 inches) per hour. The red areas are considered moderate rainfall.

For more information about how TRMM looks at rainfall, visit NASA's TRMM website at: http://trmm.gsfc.nasa.gov/. TRMM is a joint mission between NASA and the Japanese space agency JAXA.

Cyclone Ilsa is expected to track west-southwestward and gradually weaken as vertical wind shear (winds blowing in different directions at different levels of the atmosphere that tear a storm apart) will begin to increase and the sea surface temperatures drop to below 26 degrees Celsius (78 Fahrenheit). A cyclone or hurricane needs sea surface temperatures near or above 80F to maintain strength or strengthen.

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


March 19, 2009

Cyclone 22S Explodes in Growth, Becomes Cyclone Ilsa

satellite image of Ilsa Credit: NASA/JPL
> Larger image
Cyclone 22S was born yesterday and overnight has exploded into a powerful tropical cyclone in the open waters of the southern Indian Ocean. It has strengthened enough to get named Cyclone Ilsa and is packing sustained wins near 100 knots (115 mph). That makes Ilsa a Category 3 cyclone on the Saffir-Simpson Scale.

Cyclone Ilsa is located about 625 nautical miles east-southeast of the Coco Islands, near latitude 16.5 south and 106.3 east. The Coco Islands are a pair of islands located in the eastern Indian Ocean, politically administered by Burma. Geographically, they're a part of the Andaman Islands archipelago and separated from the North Andaman Island (India) by the Coco Channel. Ilsa is moving west-southwest near 10 knots (11 mph) and will continue in that general direction, not directly impacting any landmasses.

This infrared image of Ilsa was created by data from the Atmospheric Infrared Sounder (AIRS), an instrument that flies aboard NASA's Aqua satellite. The image was created on Mar. 18 at 6:35 UTC (2:35 a.m. EDT).

The AIRS image shows the temperature of the cloud tops or the surface of the Earth in cloud-free regions. The coldest cloud temperatures are in purple located around Ilsa's center. Those areas in purple have some of the strongest thunderstorms. The second-coolest temperatures are in blue, which make up the clouds outside of the center of circulation.

Scientists use the AIRS data to create an accurate 3-D map of atmospheric temperature, water vapor and clouds, all of which are helpful to forecasters.

AIRS's infrared signal doesn't penetrate through clouds. Where there are no clouds the AIRS instrument reads the infrared signal from the surface of the ocean waters, revealing warmer temperatures in orange and red. Notice the red-hot land temperatures in Western Australia.

QuikScat Clocking Wind Speed From Space

satellite image of Ilsa Credit: NASA/NRL
> Larger image
NASA's Quick Scatterometer satellite (QuikScat) has been watching Ilsa's winds by using microwaves to peer into the clouds. QuikScat can determine the speed of the storm's rotating winds from its orbit in space. This image from QuikScat shows Ilsa's wind speeds in different colors and wind direction are indicated by small barbs. The black barbs point to areas with wind speeds between 33-39 knots (38-45 mph). The purple barbs show higher wind speeds near Ilsa's center between 49-60 knots (56-69 mph). Maximum winds around the center were near 100 knots (115 mph). This image was captured on Mar. 19 at 10:36 UTC (6:36 a.m. EDT). The minimum central pressure at the time of this image was 948 millibars.

The forecast from the Joint Typhoon Warning Center notes "Favorable upper level conditions should allow further intensification over the next 12 hours. However, the cyclone will encounter decreasing along-track sea surface temperatures and slightly less favorable upper level conditions after 12 hours which should result in slow weakening."

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



March 18, 2009

Tropical Cyclone 22S Forms North of Learmonth, Northwestern Australia

satellite image of storm 22S > Larger image
Credit: NASA
The 22nd tropical cyclone has formed in the southern Indian Ocean far enough away from mainland Australia to cause residents any problems.

Tropical Cyclone 22S formed in the morning hours of March 18, and has sustained winds of 35 knots (40 mph). 22S's center was located far north of Learmonth, Western Australia, about 510 nautical miles away. That puts its center near 13.7 degrees south and 113.3 degrees east. 22S has been moving west-southwest at a speedy 15 knots (17 mph).Estimated minimum central pressure is 1000 millibars.

Satellite imagery shows "deep convection" forming in the southwest and southeast quadrants. That means rapidly rising air that gives birth to thunderstorms that add to the strength of the storm.

According to forecasters at the Joint Typhoon Warning Center, "the system is in an area of moderate vertical wind shear (winds that can tear a storm apart) and high sea surface temperatures (which power a storm). As the system tracks to the west-southwest it will move closer to an area of more favorable vertical wind shear and upper-level outflow (meaning it will be able to strengthen).

This image was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite on March 18 at 06:44 Zulu Time (2:44 a.m. EDT). The rounded shape of the clouds indicates that 22S has a good circulation and reflects the forecast that the storm is strengthening. As 22S strengthens, it is forecast to stay at sea away from land areas for the next several days.

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