Despite Canberra Airport recording only 2.8mm of rainfall to 5.30pm on Thursday, parts of the ACT did experience flooding as dams overflowed across the territory and wet weather continued into a second day.

But, in the 24 hours to Thursday morning, Canberra Airport recorded 25mm of rain, and the weather bureau has predicted more is on the way.

As of 6pm Thursday evening, emergency services had attended no major incidents. However, they had been kept busy with a steady stream of callouts for leaking roofs throughout the day.

Flood watch warnings have been issued for parts of the region, including minor flooding possible at the Queanbeyan and Molonglo rivers, and possible flooding of the upper Murrumbidgee River, Burrinjuck Dam and Coomer Creek.

Morgan Pumpa at the Bureau of Meteorology initially forecast 15 to 20mm of rain for Thursday.

There is a chance of a thunderstorm on Friday with 15 to 25mm of rain in total predicted for the day.

The weather is caused by a trough, associated with a cold front, which is moving across the far west of NSW and will continue to move east in the coming days.

"This system is expected to continue rain into the end of the weekend, before partly cloudy conditions on Monday," Ms Pumpa said.

The rain is expected to ease on Saturday, with four to 15 millimetres forecast at Canberra Airport.

However, Sunday is expected to see another increase with 10 to 25 millimetres predicted, as the trough and cold front is forecast to deepen into a low pressure system off the central southern NSW coastline.

"There are some uncertainties surrounding this second system moving over NSW over the coming days and then into the weekend. So just really important that people keep an eye on the forecast, check the warnings and also monitor a radar," Ms Pumpa said.

The ACT Emergency Service Agency received multiple calls about storm and tree damage across Canberra.

An ESA spokeswoman said most of the call outs had been for leaking ceilings and some for fallen trees.

She said the incidents were due to people not preparing for the storm and not fixing existing damage to homes.

In September, the territory recorded above average rainfall, with area-averaged rainfall being 34 per cent above the long-term average.

The national weather bureau said most of the rainfall recorded during the month was associated with cold fronts from low pressure systems passing over southern Australia.

Mean monthly maximum temperatures were close to their long-term monthly averages while minimum temperatures were around 1 degree above their monthly averages.

Total rainfall for the month at Canberra Airport was 71.4 millimetres, which is 133 per cent of the average at the current site, or 134 per cent of the average over all years of 53.3 millimetres.

Sydney officially marked its wettest year ever on Thursday, since records began in 1858. No such announcement has been made for Canberra.

Australia has entered its third consecutive La Nina. Flood warnings are in place across NSW, Victoria and QLD as Eastern Australia bears the brunt of days of drenching rain, filling already-flooded inland rivers.

A Weatherzone spokesperson said NSW would be the hardest hit state by thunderstorms this week as a trough and low pressure system moves across the states.

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