UPDATE: The State's emergency services are urging West Australians to prepare for severe thunderstorms, which are expected to continue to develop this evening.
The Bureau of Meteorology has issued a warning for damaging winds and heavy rainfall for the South West, South Coastal and Great Southern districts.
The warning affects the area bounded by Windy Harbour, Collie, York, Corrigin and Bremer Bay.
"This includes people in, near or between ... Bridgetown, Narrogin, Katanning and Albany. This does not include York," the Bureau said.
It warned that the storms might be accompanied by damaging winds and heavy rainfall, which could lead to flash flooding.
"Storms could cause damage to homes and property," the Bureau said.
"The overall weather pattern is not unusual for this time of year but severe weather may occur in some parts of the warning area."
Isolated showers and thunderstorms are expected to hit Perth early this week, with temperatures set to reach 36C on Monday and 31C on Tuesday.
The clouds should clear on Wednesday, but the temperature is expected to remain in the 30s. Perth can expect a 41C day on Saturday.
The Bureau warned on Thursday that the heatwave, which had already affected several States, would continue unabated this week.