September 9, 2009
Tropical Storm Dujuan Takes Frontal Characteristics
Hurricane Season 2009: Tropical Storm Dujuan (Western Pacific)
Tropical cyclones can either dissipate at sea or on land, become extra-tropical, or merge with cold fronts. Tropical Storm Dujuan is becoming extra-tropical and has elongated. In fact, the storm has elongated so much that it has developed frontal characteristics over the last day and NASA satellite imagery depicts the storm's change in shape.
NASA's Aqua satellite flew over Tropical Storm Dujuan at 10:53 p.m. EDT last night, September 8 and captured an infrared and visible image of the storm's clouds from the Atmospheric Infrared Sounder (AIRS) instrument. Both AIRS images showed Dujuan's clouds are stretched from northeast to southwest almost resembling more of a cold front than a tropical storm, although the center of Dujuan's circulation is still visible in both images.
At 8 a.m. EDT today, September 9, Dujuan was still transitioning into an extra-tropical storm, and still maintained a warm core. When storms transition to extra-tropical status they become cold core storms. At that time, Dujuan's center was located 945 miles south of Petropavlovsk, Russia, near 38.4 north and 157.9 east. It was moving northeastward near 34 knots (39 mph) and is forecast to speed up as it becomes a cold core system (much like a typical northern hemisphere low pressure system). Its maximum sustained winds were still near 55 knots (63 mph), and it was still producing 19 foot-high seas. Dujuan is forecast to maintain its intensity and continue producing high seas in its path into the Northern Pacific Ocean.
The system is currently tracking over cooler waters around 75 degrees Fahrenheit (tropical cyclones need sea surface temperatures at least near 80 F to maintain intensity) as transitions to an extratropical cyclone. A recent NASA Aqua satellite image from the Advanced Microwave Sounding Unit (AMSU) instrument showed that Dujuan still has deep convection (strong thunderstorms) near its center, although the strongest storms are northwest of the center.
Rob Gutro, NASA/Goddard Space Flight Center
September 8, 2009
NASA's QuikScat Sees Dujuan Intensify While Moving Away from Japan
Dujuan is a tropical cyclone that keeps hanging on as it moves east-northeast away from Japan, and NASA's QuikScat imagery noticed that its sustained winds intensified over the last day from 46-57 mph because environmental conditions are helping it.
On Monday, September 7, forecasters expected Dujuan to become extra-tropical by the end of the day, but it held onto its tropical storm status for one more day. Today, September 8, the sustained winds were near 50 knots (57 mph), and Dujuan had moved to a position 305 nautical miles southeast of Toyko, Japan, near 32.3 north and 144.0 east. Dujuan was moving east-northeasterly near 21 mph.
The Joint Typhoon Warning Center (JTWC) noted in their recent discussion "Animated infrared imagery shows that central convection is continuing to persist over a well developed low level circulation center as indicated in a 0846 Zulu Time (4:46 a.m. EDT) Quikscat pass which depicts 45- to 50-knot unflagged winds." NASA's Quick Scatterometer satellite (QuikScat) analyzes and determines rotating surface wind speed of a tropical cyclone by using microwaves to peer through the clouds.
The JTWC also noted "Though the deep convection has indeed shifted to the northeast quadrant of the storm, recent microwave images (September 8 at 7:26 a.m. EDT (1126 Zulu Time) from the Advanced Microwave Sounding Unit (AMSU) on NASA's Aqua Satellite) still show central convective organization."
Warm sea surface temperatures and moderate wind vertical wind shear are allowing Dujuan to keep going in the Western Pacific Ocean.
Data from the Atmospheric Infrared Sounder (AIRS), an instrument that flies aboard NASA's Aqua satellite was used to create a visible image of Dujuan on September 7 at 11:47 p.m. EDT.
AIRS also captured temperature of the high, cold, cloud tops in Dujuan and identified them as cold as or colder than 220 degrees Kelvin or minus 63 degrees Fahrenheit (F). 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.
Dujuan should be transitioning into an extra-tropical storm by tomorrow.
Rob Gutro (from NHC discussion), NASA/Goddard Space Flight Center
September 4, 2009
Tropical Depression Dujuan Fighting to Live
Tropical Depression Dujuan formed early today, September 4, and is fighting upper level winds to stay alive some 465 miles south-southeast of Okinawa, Japan.
Tropical Depression Dujuan, also known as storm 13 W (for the thirteenth tropical cyclone in the western Pacific Ocean) had maximum sustained winds near 40 mph earlier today. It was located near 19.0 north and 131.1 east, and moving northeast around 15 mph.
The Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite flew over the large Tropical Storm Dujuan and revealed cold high, thunderstorm clouds, as cold as -63F on September 3 at 1:11 p.m. EDT. Infrared imagery shows the temperature of the cloud tops which gives a hint about the power of the thunderstorms in a tropical cyclone. The colder the clouds are, the higher they are, and the more powerful the thunderstorms are that make up the cyclone.
The storm is forecast to move north-northeast and is forecast to move east of Japan, with its center staying at sea. On its track into the open waters of the Western Pacific Ocean it is expected to get close enough to Japan to bring rain there over the weekend.
Rob Gutro, NASA/Goddard Space Flight Center