If you're waiting for relief from the hot weather, you're likely to be disappointed as Perth looks set to have its longest heatwave in 20 years.

The Bureau of Meteorology says residents are set to swelter with nine days straight of temperatures in the mid to late 30s. A heatwave is when there is three consecutive days over 35C.

Perth temperatures have reached 35C or higher since Sunday and weather experts say there is no reprieve in sight.

Tomorrow's temperature is forecast to top 37C followed by temperatures of 38, 36, 38, 39, and 37. The minimum expected until Monday is a warm 22C.

WA Bureau of Meteorology climate information officer John Relf said that if the forecast temperatures eventuated, Perth could be in the middle of the longest heatwave for 20 years. The record was 10 days in 1975.

A strong high system and the low pressure system threatening to turn into a cyclone in the Kimberley region tomorrow morning are blamed for the scorching temperatures.

Meteorologist Scott Carpentier said the combination of the two systems was pushing a lot of hot, dry air from inland Australia across the continent and into metropolitan Perth.

"Basically it's becoming a little bit more heated every day as we go along and we are likely to be some of the hottest temperatures in Australia over the next few days," Mr Carpentier said.

"That wind stream is travelling right across the continent and heating up with the sun during the daytime."

Mr Carpentier said Perth's maximum temperatures would be equivalent to tropical areas in northern Australia. Hot dry air was expected to make life uncomfortable in Perth in coming days and coastal residents could experience some humid evenings.

January saw above average temperatures in Perth, with February on target to be a similar story, the bureau says.

Power consumption hit record levels on Monday.

Western Power spokeswoman Marisa Chapman said power use hit an all time high at 4.52pm as peak usage hit 3625MW.

Ms Chapman said that it was the most electricity used in the network at any one point in time ever. New homes being constructed and higher airconditioner use was thought to be behind the soaring power use.

On Sunday power consumption peaked at 2952MW at 6.04pm. Last summer's peak usage - 3574MW on March 17 - has been passed twice so far this summer, she said.