Canberra received 6.6mm of rain between 9am and 2.35pm, and the Bureau of Meteorology is predicting more wet weather into the evening.
A severe weather warning for heavy rain is in place for the ACT and central and southern NSW on Thursday.
The bureau is warning heavy rain may lead to flash flooding, and urging people not to drive, ride or walk through floodwater, and to keep clear of creeks and storm drains.
A duty forecaster at the bureau's Canberra office said it was likely rain in the ACT would increase over the morning, with the heaviest falls in the afternoon.
"Probably the worst of it will be this afternoon and then this evening it should be tailing off, so maybe easing back to a few showers in the evening," he said.
The forecaster said Canberra looked likely to receive 30 to 50mm rain today, and humidity levels were currently sitting at 90 per cent.
"It's very tropical at the moment, once we actually get to the back edge of this rain band things will start drying out and tomorrow will be a lot more comfortable," he said.