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Tropical Low Prompts Watch for Western Australia

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The potential risk posed by a Tropical Low over the South Indian Ocean prompted the Australian Bureau of Meteorology to issue a Watch for a portion of the coast of Western Australia on Wednesday evening.  The Tropical Low is currently designated as Invest 91S by the U.S. Joint Typhoon Warning Center.

At 10:00 p.m. EST on Wednesday the center of the Tropical Low was located at latitude 11.4°S and longitude 118.9°E which put the center about 510 miles (825 km) northwest of Broome, Australia.  The Tropical Low was moving toward the southeast at 6 m.p.h. (10 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1001 mb.

The Australian Bureau of Meteorology issued a Watch for the portion of the coast of Western Australia from Bidyadanga to Mitchell Plateau.  The Watch included Broome and Derby.

The circulation of the Tropical Low was in the early stages of organization on Wednesday evening.  There were not many thunderstorms near the center of the Tropical Low.  Thunderstorms were occurring in a band in the southern periphery of the circulation around the Tropical Low.  There also were not many thunderstorms in the northern side of the Tropical Low.

The Tropical Low will move through an environment favorable for the formation of a tropical cyclone during the next 24 hours.  The Tropical Low will move over water where the Sea Surface Temperatures are near 30°C.  It will move under the middle part of an upper level ridge that is northwest of Australia.  The upper level winds are weak in the middle of the ridge and there will be little vertical wind shear.  The Tropical Low is likely to continue to get better organized during the next 24 hours.

The Tropical Low Will move around the western side of a high pressure system over Australia.  The high pressure system will steer the Tropical Low toward the southeast during the next 24 hours.  On its anticipated track, the Tropical Low will approach the coast of Western Australia in 48 hours.

Tropical Low Forms Northwest of Australia

A Tropical Low formed over the South Indian Ocean northwest of Australia on Saturday.  At 1:00 p.m. EST on Saturday the center of a Tropical Low was located at latitude 14.3°S and longitude 121.9°E which put it about 255 miles (410 km) north of Broome, Australia.  It was moving toward the south-southwest at 4 m.p.h. (6 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1002 mb.

A Watch was issued for the portion of Western Australia from Mitchell Plateau to Wallal Downs.

The circulation around the Tropical Low was still organizing.  It did not have a well developed center of circulation.  There was a clockwise rotation around a broad center.  Bands of showers and thunderstorms were beginning to form in the outer regions of the circulation.  Upper level divergence was pumping mass away from the Tropical Low and the surface pressure was decreasing.

The Tropical Low will move through an environment favorable for intensification during the next 24 to 48 hours.  It will move over water where the Sea Surface Temperature is near 30°C.  The Tropical Low will move through a region where the upper level winds are weak and there will be little vertical wind shear.  The Tropical Low is likely to intensify into a named tropical cyclone and it could strengthen into the equivalent of a hurricane/typhoon.

The Tropical Low will move around the western end of a high pressure system centered near the north coast of Australia.  The high will steer the Tropical Low toward the south-southwest.  On its anticipated track the Tropical Low could approach the coast of Western Australia southwest of Cape Leveque in a day or two.