Heavy falls have prompted forecasters and emergency services to warn of possible flash flooding across south-eastern NSW.
But meteorologists say Canberra should escape most of the severe weather swamping parts of the southern highlands and the south coast.
Weatherzone's Ben McBurney said Canberra had not received as much rain as further east, with Monday's predicted falls not enough to cause flooding
Canberra could also get more than half last month's total rainfall lash the city this week, with up to 25 millimetres expected on Monday alone. Only 35 millimetres fell in the capital during December.
The wet weather and cloudy skies are set to break up the hot spell the ACT has seen in the past few days, with maximum temperatures forecast to stay within the 20s in the coming week.
The Bureau of Meteorology on Monday issued a severe weather warning as the NSW south coast and southern NSW braced for falls of between 50 and 70 millimetres.
Batemans Bay, Braidwood, Bowral, Moruya Heads, Araluen and Nerriga are among the areas expected to be saturated by heavy falls, with localised falls of up to 140 millimetres possible across the 24-hour period.
The NSW State Emergency Service warned campers on NSW south coast rivers to move to higher ground and establish an evacuation route early on Monday morning, with more heavy rain on the way.
Since 9am on Sunday, 110 millimetres has fallen at Bodalla Post Office and 108 millimetres was recorded at Mt Darragh.
Moruya received124 millimetres while Regatta Point notched up 100 millimetres.
The Snowy Mountains recorded huge falls too, with 75 millimetres falling in Perisher Valley and 68 millimetres at Thredbo.
Clyde Mountain also picked up 100 millimetres in the past 24 hours.
Motorists planning on travelling through that area should delay their journey, Sean Carson of the Bureau of Meteorology told ABC radio.
A NSW Traffic Management Centre spokeswoman said there were no reported state road closures as of 8.40am.
In the ACT, the southern Googong foreshores have been closed due to the wet weather conditions, an ACT Government spokesman said.
Mr McBurney said that while the rain was expected to continue throughout Monday, it should ease into Tuesday and clear by Wednesday.
The SES has advised people in flood-affected areas not to drive, ride or walk through flood water and to keep clear of creeks and storm drains.
If you are trapped by flash flooding, seek refuge in the highest available place and ring 000 if you need rescue.
For emergency help in floods and storms, call your local SES Unit on 132 500.