Residents in Perth and the south-west of the state are are being warned to prepare for more severe weather.
A cold front over the southern half of the state overnight has dumped 42 millimetres of rain in Perth.
Rottnest recorded 61 millimetres and wind gusts of more than 90 kilometres an hour.
Jandakot, Swanbourne and Garden Island have had more than 50 millimetres of rain.
The State Emergency Service has received 37 calls for assistance, mostly in Perth, for water damage and flooding.
Western Power says about 300 homes and businesses in Mullewa, east of Geraldton, lost power during the storm.
Services are expected to be restored by mid morning.
If anyone comes across fallen powerlines, they are urged to contact Western Power.
The Bureau of Meteorology is forecasting severe weather to hit the southern half of the state late tonight.
© ABC 2013
11:06 EDT El Nino is one extreme of the El Nino-Southern Oscillation (ENSO) phenomena, in which La Nina is its counterpart.