Perth reached 35.7C today but the mercury is set to plunge by more than 10 degrees on Friday, leading into a wet weekend.
The temperature in the city peaked just before 2:00pm, with Pearce north-east of Perth recording a high of 37.4C around the same time.
A possible late thunderstorm about the hills was also forecast with gusty evening winds.
But the hot weather won't carry through into the weekend, with showers predicted for Friday and another thunderstorm, along with a maximum of just 25C.
Saturday will be 24C and rainy, with Sunday reaching 25C.
Bureau of Meteorology duty forecaster Mark Paull said a cold pall and a front moving thorough on the weekend would to cool things down.
"The change (of 11 degrees), it's more likely spring-type conditions when we get the big fluctuations in temperatures going up and down," he said.
"It's not unheard of through basically November for those conditions to continue."
Mr Paull said the Perth metro average temperature for November was 26.6C.
Today's weather was still a way off the highest maximum ever recorded in November of 40C, while the lowest maximum was 15.8C.
A thunderstorm warning remains this morning in place for parts of the South West, Lower West and Great Southern regions.
Affected towns include Dwellingup, Harvey, Collie, Williams, Kojonup and Manjimup.
Outside of Perth, showers and thunderstorms were predicted for the Kimberley, Interior, inland Gascoyne, northern and western Goldfields and all but the far eastern parts of the South West Land Division.ABC