Rain has forced the third day of the third Test between Australia and South Africa at the SCG to be abandoned without a ball being bowled on Friday.

Persistent downpours in Sydney mean Australia captain Pat Cummins faces a dilemma on when to declare with his side in complete control at 475-4 with Usman Khawaja (195*) and Matthew Renshaw (5*) at the crease.

Time is running out for Australia to complete a clean sweep of the three-game Test series, after 57 overs were lost on the opening two days before Friday's complete washout.

The Sydney forecast is for improved weather on the remaining two days, with a shower or two predicted for Saturday, followed by partly cloudy conditions without any rain on Sunday.

There are 196 overs remaining in the Test, meaning Cummins will need to be decisive, but likely will allow Khawaja to reach a maiden double hundred.

Australia will be motivated to secure the victory clinch their first-ever spot in the ICC World Test Championship final to be played in June.

The Aussies are due to travel to India for a four-game Test series starting in February.

Sydney's rain curse persists

Sydney's poor run of rain impacting Tests in January continues, with a total of 25 days washed out due to rain in 110 Test matches at the SCG. Over the past eight years, 64 per cent of days during the SCG Tests have been impacted by rain.

Elsewhere, Perth has never had an entire day's play washed out, while Hobart (one) and Adelaide (two) have had minimal issues, while Brisbane and Melbourne have lost eight and nine full days respectively.