As the remains of Tropical Cyclone Isobel merged with a deep low pressure system over Western Australia's southern coast, communities braced for violent gusts of up to 120 kilometres (75 miles) an hour and torrential rains.

"It looks as though peak wind speeds are going to occur during this evening before the low slowly moves away to the southeast," Caroline Bojarski of the West Australian Weather Bureau said.

Dubbed a "perfect storm" by meteorologists, the rare weather system had dumped almost 100 millimetres (3.94 inches) of rain by the afternoon, Fire and Emergency Services Association spokesman Mike Venn said.

Some 92 mm of rain had fallen in coastal Esperance since 9.00 am and another 90 mm was possible before midnight, he said.

"We've already got localised flooding in town, we've got our ... units out doing a lot of sandbagging ... so if we get another 90 mm that could be just exacerbated a little bit more," he said.

"A few streets in the Esperance townsite have been closed due to flooding, with drains blocking up and threatening people's homes."

Further east, a massive 134 mm fell on Baladonia, doubling the previous record for a day's rain.

Earlier in the day as as the storm swept southward, a 75 mm deluge forced resources giants BHP Billiton and Minara Resources, the country's two largest nickel producers, to cease pit operations.

However oil producers Woodside Petroleum and Santos Ltd, which had both halted activities ahead of Tropical Cyclone Isobel's northwestern landfall Wednesday, expected their operations to be back online by Saturday and Friday respectively.

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