The rival Ashes teams and thousands of cricket spectators are set to endure four successive days of 38C or higher when the third Test begins tomorrow.
Today is forecast to reach 35C and temperatures are tipped to hover above this point for six consecutive days, which has only occurred six times in December since 1897.
Tomorrow's maximum will rise to 38C and there will be little respite, with maximums of 38C also expected on Saturday and Sunday before rising to 39C on Monday.
Neil Bennett from the Weather Bureau said after a cooler start to summer, with an average of 27C so far this month, the warmer weather would come as a shock.
"From Thursday to Tuesday we'll have 35C or higher for every one of those days - it's not pleasant," he said. "It is slightly unusual for the length of the hot temperatures."
Mr Bennett stopped short of predicting a heatwave because to meet the criteria Perth would need to experience an average daily temperature of 32C or above - across 24 hours - over three days.
The first three days of the third Test are sold out, with less than 2500 tickets available for the fourth day.
A number of tickets have appeared at inflated prices on websites such as eBay and Gumtree, but Cricket Australia executive general manager of operations Mike McKenna warned people against buying from scalpers.
"On many occasions fans have forked out well beyond their means, to discover on the day of the event that they've been duped by scalpers," Mr McKenna said.
St John Ambulance operations manager Jae Smith said it was important for spectators to wear sun protection, space their alcoholic drinks and drink plenty of water to avoid dehydration.
"The main thing is to look after your mates, and if any of them are looking like they need medical assistance they should make themselves known to medical people," she said.
With conditions ripe for booze- related trouble, WA Police has warned it will crack down on excessive drinking and troublemakers at the cricket, beaches and nightlife hotspots over the weekend. More officers will be on the beat in the Perth CBD, Northbridge, Fremantle, Hillarys, the WACA Ground and pubs.
Cdr Charlie Carver said police would take a zero-tolerance approach to drunkenness.
"This is about targeting those people who are committing those antisocial behaviour moments where there could be aggression, fights and other kinds of behaviours," he said.