After a record hot day in Perth on Saturday, the following 24 hours were the wettest in September since 1988.
In the 24 hours until 9am on Monday, Perth received 35.8 millimetres of rain.
This was the most rain since September 14 of 1988, when a record 51.8 millimetres of rain fell.
The rain and cool change followed a top of 34.5 degrees on Saturday, which was the hottest recorded September temperature for Perth.
Bureau of Meteorology duty Forecaster Luke Huntington said it was "very unusual" to see such a rapid change in weather from one day to the next.
He said a strong cold front with an associated cold pool generated cooler temperatures on Sunday.
A top of 21.7 was recorded in Perth on Sunday morning before temperatures dropped.
There could be a few more showers on Monday morning and a top of 18 degrees is forecast.
Forecast for the rest of the week:
Tuesday: partly cloudy 8-19
Wednesday: partly cloudy 10-22
Thursday: possible shower 11-22
Friday: partly cloudy 12-23
Saturday: showers 14-21
