Tag Archives: South Indian Ocean

Tropical Cyclone 03S Moving West of Australia

A tropical cyclone designated 03S moved farther west of Australia and weakened on Saturday.  Tropical Cyclone 03S moved across northern Australia as a low pressure system last week before move off the coast near Broome.  After the center of the low moved over the South Indian Ocean thunderstorms developed near the core of the system and the Australian Bureau of Meteorology classified it as a tropical low.  The tropical low strengthened into the equivalent of a tropical storm on Friday night, but the Australian Bureau of Meteorology did not give the system a name.

At 7:00 p.m. EST on Saturday the center of Tropical Cyclone 03S was located at latitude 19.5°S and longitude 109.8°E which put it about 335 miles (540 km) northwest of Learmonth, Australia.  Tropical Cyclone 03S was moving toward the west at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 994 mb.

Tropical Cyclone 03S has a well defined low level circulation but the distribution of thunderstorms is asymmetrical.  Most of the stronger thunderstorms are forming in bands west of the center of circulation.  There are also bands in the eastern half of the circulation but they consist primarily of low clouds and rain showers.  Strong easterly winds in the upper levels are shearing the tops off of any thunderstorms that develop in the eastern part of the circulation.  The easterly winds are also inhibiting upper level divergence to the east of the center.

Tropical Cyclone 03S will move into an environment that will be unfavorable for intensification.  Tropical Cyclone 03S is moving over water where the Sea Surface Temperature is near 26°C, but it will move over cooler water during the next several days.  An upper level ridge centered over Australia is generating easterly winds which are blowing across the top of the tropical cyclone.  The easterly winds are causing moderate vertical wind shear and are responsible for the asymmetrical distribution of thunderstorms.  Tropical Cyclone 03S is likely to weaken slowly during the next several days.

A subtropical ridge will continue to steer Tropical Cyclone 03S to the west during the next few days.  On its anticipated track Tropical Cyclone 03S is expected to move farther away from Western Australia as it weakens.

Tropical Low Forms Over Western Australia

An area of low pressure system has been moving across northern Australia during the past few days.  The low remains organized and the Australian Bureau of Meteorology classified the system as a Tropical Low on Wednesday because of the potential for it to develop into a tropical cyclone.  At 10:00 a.m. EST on Wednesday the center of the Tropical Low was located at latitude 15.9°S and longitude 127.0°E which put it about 80 miles (130 km) west-southwest of Wyndham, Australia.  The Tropical Low was moving toward the west at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) an there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1002 mb.

There is a well defined cyclonic circulation in the lower levels of the atmosphere, but there are not many thunderstorms in the core of that circulation.  Most of the thunderstorms are developing in bands that are on the periphery of the circulation.  The strongest thunderstorms are forming in bands in the western portion of the circulation as that part of the Tropical Low begins to moves over water.  The strongest winds are also occurring in these thunderstorms that are over water.  The Tropical Low is moving underneath an upper level ridge and the ridge is causing upper level divergence which is pumping out mass.

The core of the Tropical Low is still over Western Australia and moving over land is the primary factor inhibiting intensification of the system.  The atmospheric environment is favorable for intensification.  The upper level ridge is producing light winds over the Tropical Low and there is little vertical wind shear.  The Sea Surface Temperature of the water west of Australia is near 30°C and there will be plenty of energy in the ocean to support strengthening when the core of the circulation moves west of Australia.  Some slow organization of the circulation is possible during the next 12 hours as the core of the Tropical Low moves closer to the coast of Western Australia.  Further intensification is likely during the next several days once the core of the Tropical Low moves over the warm water.  The Tropical Low could strengthen into the first named tropical cyclone of 2017 later this week.

The upper level ridge is producing light easterly winds which are slowly steering the Tropical Low toward the west.  That general motion is expected to continue for another day or so.  Eventually, the Tropical Low is forecast to move on a west-southwesterly track that would paralle, but keep it to the west of the coast of Western Australia during the next several days.