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Hurricane Season 2009: Hettie (South Pacific Ocean)
01.29.09
 
Jan. 29, 2009

AIRS image of Hettie from Jan. 29, 2009> Larger image
Credit: NASA JPL/ Ed Olsen
No Detective Needed, Tropical Cyclone Hettie Already Dissipating at Sea

Hettie is going to be a very short-lived storm. She has already weakened due to adverse atmospheric conditions and is already dissipating over the open waters of the southern Pacific Ocean.

Unlike her fictional British namesake Hettie Wainthropp, a private investigator from the book "Missing Persons," by David Cook, it doesn't take a detective to figure out that this tropical cyclone won't be around over the weekend of Jan. 31-Feb. 1.

On January 29 at 0300 UTC (10 p.m. EST Jan. 28), the Joint Typhoon Warning Center, the organization responsible for forecasting tropical cyclones in this region, issued their second, and final bulletin on Cyclone Hettie. At that time, Hettie's maximum sustained winds were near 30 knots (34 mph) and weakening. Her center was located about 390 miles southeast of Suva, Fiji. That's near 22.5 degrees south latitude and 177.8 west longitude.

NASA's Aqua satellite flew over Hettie and the Atmospheric Infrared Sounder (AIRS) instrument onboard captured this image of her cloud temperatures on Jan. 29 at 0135 UTC (Jan. 28, 8:35 p.m. EST). In this satellite image, Hettie appears as a very ragged circular area, with no eye. That's an indication of a weaker storm.

The AIRS infrared images show the frigid cloud top temperatures, giving 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, and there are two small such areas on this AIRS image. Lower, less cold clouds are depicted in blue, which are around 240 degrees Kelvin, or minus 27F.

Hettie will likely transition into a remnant low before the weekend arrives.

Text credit: Rob Gutro/NASA Goddard Space Flight Center


Jan. 28, 2009

Hettie Forms in the Southern Pacific Ocean

AIRS image of Hettie Credit: NASA/JPL
> Larger image
A new tropical storm named Hettie formed in the warm waters of the Southern Pacific Ocean today and it looks like that's where she'll stay until she fades by the end of the week.

Hettie is the 11th tropical cyclone in the southern Pacific Ocean this season. At 1500 Zulu Time (10 a.m. EST) on Jan. 28, her center was near 22.0 degrees south latitude and 177.7 degrees west longitude or approximately 315 nautical miles southeast of Suva, Fiji.

Fiji is an island nation in the South Pacific Ocean east of Vanuatu, west of Tonga and south of Tuvalu. Fiji consists of an archipelago of about 322 islands, 106 of which are inhabited. Most of the population resides on the two major islands, Viti Levu and Vanua Levu. Fiji lay to the east of Australia. The total distance from Australia to Fiji is 2,927 miles (or 4,711 kilometers or 2,544 nautical miles).

Hettie had maximum sustained winds near 35 knots (42 mph), with a minimum central pressure of 1000 millibars and was moving south-southwestward at 7 knots (8 mph).

The infrared imagery of the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite is used to identify the cloud temperatures in tropical cyclones. It captured this image of Hettie on Jan. 28 at 00:59 Zulu Time (7:59 p.m. EST on Jan. 27). The comma like shape of the storm is an indication that it's still not very well organized although there are some very cold temperatures (in purple).

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, which mean a stronger tropical cyclone.

The infrared image also shows a large 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 Hettie's high clouds. 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.

According to the Joint Typhoon Warning Center (JTWC), the organization that forecasts for tropical cyclones in the southern Pacific Ocean, recent animated infrared imagery (such as that from the AIRS instrument) and microwave image shows deep convection flaring on the southeastern periphery of Hettie's low level circulation center. An analysis of the upper atmosphere from the JTWC shows a "favorable environment, although moderate westerly vertical wind shear (winds that can weaken a storm) continues to limit significant development of the system."

Hettie is expected to maintain her strength over the next 12 hours and then begin to weaken as vertical wind shear (winds that tear a storm apart) increases and convection is sheared away from center due to an approaching mid- to upper-level shortwave trough (an extended area of low pressure). Hettie is expected to dissipate over water sometime on Friday.

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