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Hurricane Season 2008: Anika (Indian Ocean)
 
Nov. 21, 2008

Tropical Storm Anika and Tropical Cyclone 03S Both Fading

AIRS image of Anika and O3S on November 21, 2008> Larger image
Credit: NASA JPL
This weekend is a killer for tropical cyclones in the Indian Ocean. Both Tropical Storm Anika and Tropical Cyclone 03S are both meeting their end over the weekend of Nov. 22-23.

Anika be a tropical storm on Friday, Nov. 21, but by Saturday, Nov. 22, when the storm is expected to make landfall north of Port Headland, Australia, it will quickly weaken into a remnant low pressure area.

Meanwhile, on Nov. 21-22, Tropical Cyclone 03S is fading in the same area. 03S is passing south of the Cocos Islands, located south of the Isle of Java. That puts 03S to the northwest of where Anika is located.

Where is Anika?

On Nov. 20 at 21:00 Zulu Time (4:00 p.m. EST), the Joint Typhoon Warning Center issued its final advisory on Anika. At that time, Anika had sustained winds near 35 knots (40 mph) that were quickly waning. Anika was 650 miles northwest of Learmonth, a city in northwestern Australia. It was near 15.5 degrees south latitude and 105.7 degrees east longitude and moving southeastward near 13 knots (15 mph). It will continue moving in that direction until it makes landfall this weekend. Anika continues to deal with strong vertical wind shear (winds blowing in different directions at different levels of the atmosphere that tear a storm apart) and cooler sea surface temperatures. Ocean waters of at least 80 degrees Fahrenheit are needed to power tropical cyclones.

Where is Tropical Cyclone 03S?

Tropical Cyclone 03S formed behind Anika, which was also called Tropical Cyclone 02S, and is following Anika's path. That's not good news for keeping 03S alive, because the conditions Anika are in are unfavorable, and include cooler sea surface temperatures and wind shear. That explains why Tropical Cyclone 03S is fading, too.

On Nov. 20 at 21:00 Zulu Time (4:00 p.m. EST), the Joint Typhoon Warning Center issued its final advisory on 03S. At that time, it has maximum sustained winds near 25 knots (29 mph). It was about 620 miles west of Cocos Island, moving near 27 knots (31 mph). 03S will fade over the weekend of Nov. 22-23 at sea.

NASA's Aqua Satellite Captures Both Storms

NASA's Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured this visible image of both 03S (located in the top left corner of the image), and Anika, located in the left center of the image). The eastern-most part of Tropical Cyclone 03S is on the left top edge of this satellite image, while most of Anika is clearly visible from this satellite overpass. Both storms will have faded away by Monday, Nov. 24.

Text Credit: Rob Gutro/NASA's Goddard Space Flight Center


Nov. 20, 2008

Anika Maintaining Strength, Eyeing Northwestern Australia

AIRS image of Anika from Nov. 20, 2008> Larger image
Credit: NASA JPL
Tropical Storm Anika is holding its own, and is now targeting a landfall in northwestern Australia, between the towns of Port Hedlund and Learmonth by Nov. 22.

On Thursday, Nov. 20 at 1500 Zulu Time (10:00 a.m. EST), Anika had maximum sustained winds near 50 knots (57 mph) with higher gusts. She was located about 705 miles west-northwest of Learmonth, near 16.1 degrees south latitude and 104.3 degrees east longitude. Anika was moving southeastward at 15 knots (17 mph).

Several Factors Affecting Anika

Wind shear, a low pressure area, and warming cloud top temperatures all mean weakening for Anika over the next couple of days. Vertical wind shear has increased in excess of 30 knots as an upper level trough (an elongated area of low pressure) moves toward the cyclone from the southwest, diminishing convection, the rapidly rising air that forms thunderstorms, to southeast. Cloud tops have also begun to warm in response to cool sea surface temperatures. The system will continue to track generally southeast-ward for the first 36 hours then move towards the east as the system weakens. Continued moderate to high vertical wind shear and cool sea surface temperatures will further weaken the cyclone.

NASA Satellites Capture those Cloud Temperatures

As mentioned above, cloud top temperatures were used to determine if the storm is weakening or strengthening. Forecasters look at data from the Atmospheric Infrared Sounder (AIRS) instrument that flies on NASA's Aqua satellite. When cloud temperatures get colder, it means that clouds are getting higher. Building clouds indicate a lot of "uplift" in the atmosphere and stronger thunderstorms. The data from AIRS is also used to create an accurate 3-D map of atmospheric temperature, water vapor and clouds, all of which are helpful to forecasters.

The infrared image, taken on Nov. 19 at 1:59 p.m. EST (18:29 UTC) shows a huge temperature difference between the tops of the clouds in a tropical cyclone and the warm ocean waters that power it. The lowest temperatures (in purple) are associated with high, cold cloud tops that make up the top of the storm. 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. Anika is the circular purple and blue area, south of the island of Java.

AIRS infrared signal doesn't penetrate through clouds, so where there are clear skies AIRS reads the infrared (heat) signal from the ocean and land surfaces, revealing warmer temperatures (colored in orange and red). The orange temperatures are 80F (300 degrees Kelvin) or greater (the darker they are, the warmer they are). Tropical cyclones need sea surface temperatures of 80F to strengthen and maintain their strength.

Text Credit: Rob Gutro (from JTWC reports), NASA's Goddard Space Flight Center


Nov. 19, 2008

Tropical Storm Anika Passing South of the Isle of Java

Satellite image of Anika Credit: NASA's Jet Propulsion Lab
> Larger image
Tropical Storm Anika formed in the Indian Ocean late in the day on November 18, and was passing south of the Island of Java on its way to northwestern Australia by the next day.

At 1:00 a.m. EST on Nov. 19, Tropical cyclone 02s, also called Anika, had maximum sustained winds near 35 knots (40 mph). Anika was located approximately 50 miles east-northeast of Cocos island in the Indian Ocean, near 11.8 degrees south latitude and 997.7 east longitude. Was moving east-southeast near 15 knots (17 mph).

The Joint Typhoon Warning Center noted that the system will move into an area of cooler sea surface temperatures and moderate to strong vertical wind shear (winds that tear a storm apart) after 24 hours, which will begin to weaken it.

Some of the satellite data that forecasters use to determine if a storm will hold together, dissipate or strengthen are cloud temperatures. They look at data from the Atmospheric Infrared Sounder (AIRS) instrument that flies on NASA's Aqua satellite. When cloud temperatures get colder, it means that clouds are getting higher. Building clouds indicate a lot of "uplift" in the atmosphere and stronger thunderstorms. The data from AIRS is also used to create an accurate 3-D map of atmospheric temperature, water vapor and clouds, all of which are helpful to forecasters.

The infrared image, taken on Nov. 18 at 12:29 p.m. EST (17:29 UTC) shows a huge temperature difference between the tops of the clouds in a tropical cyclone and the warm ocean waters that power it. The lowest temperatures (in purple) are associated with high, cold cloud tops that make up the top of the storm. 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 infrared signal doesn't penetrate through clouds, so where there are clear skies AIRS reads the infrared (heat) signal from the ocean and land surfaces, revealing warmer temperatures (colored in orange and red). The orange temperatures are 80F (300 degrees Kelvin) or greater (the darker they are, the warmer they are). Tropical cyclones need sea surface temperatures of 80F to strengthen and maintain their strength.

Text Credit: Rob Gutro (from JTWC reports), NASA's Goddard Space Flight Center