There has been substantial rain overnight in the southern half of the state.

Perth received 27 millimetres of rain since 9:00 am yesterday to lift the monthly falls to 154.4 millimetres, well past the average of 133 millimetres.

It has been the wettest August in Perth since 2004.

The southern Perth suburb of Jandakot has had 49 millimetres in the past 24 hours.

There has also been some good falls in the wheatbelt with Dalwallinu recording 17 millimetres and Southern Cross 10 millimetres.