State Emergency Services (SES) manager Chris Stickland said the storm was a sign of things to come this winter.
But he said the weather was not as bad as the Bureau of Meteorology predicted.
"There was so much rain that people's homes flooded," he said.
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READ NOW"We had 20 jobs throughout Mandurah; 10 on Saturday and 10 on Sunday."
He said people needed to learn from the weather at the weekend and get themselves storm ready.
"This is a wake-up for storm season," he said.
"Storm season damage costs are more significant than fires and cyclones.
"It's important for people to prepare."
The SES rain gauge recorded 30cm of rain from 12am on Saturday through to Sunday.
"The further south west you went, the worse the weather was," he said.
"Some areas had more rain though and some had less."