The sweltering conditions experienced by much of the southern Wheatbelt and south-east coast has broken several records, according to the Bureau of Meteorology.
Newdegate, Lake Grace, Ravensthorpe and Esperance are among the towns to have broken records during the heatwave over recent days, while the Wheatbelt town of Hyden has been one of the worst affected, suffering four straight days of 41 degrees or higher.
Esperance set the most notable record yesterday, breaking its previous mark for the hottest ever December day.
It recorded a top of 45.3 degrees at 1.23pm, beating the previous mark of 44.9 degrees set on December 29, 2009.
It was an astonishing 24.8 degrees above the town's maximum temperature just five days earlier.
Newdegate and Lake Grace both recorded three consecutive December days with maximum temperatures above 40 degrees from Saturday to Monday, for the first time.
Both those towns saw those runs end on Tuesday but with little reprieve, both recording maximums just under 40.
Ravensthorpe's streak of four consecutive days above 38 degrees, capped by a maximum over 42 yesterday, is also the first time that's happened in December in the south coastal town.
The bureau's Neil Bennett says relief from the unusually prolonged run of hot weather for the south-east coast and lower grainbelt will finally come from today.
"It looks as if temperatures for many parts will drop quite dramatically, in fact Newdegate is expecting a maximum of only 28, so that's a massive drop there," he said.
"Similarly for Hyden 33, Ravensthorpe 25, Esperance 24 and Lake Grace 30, so a significant change moving through."
Mr Bennett says the conditions that have been bringing the hot spell are moving further east.
"That hasn't been moving anywhere but it is slowly moving, we've got a very weak front moving in from the South West and that's going to push that trough inland further to the east," he said.
"Then we'll see the heat developing out further towards the Nullabor and those sorts of areas."
Mr Bennett says the conditions have resulted from those which brought a long hot spell to Perth late last week moving further inland.
© ABC 2013
17:34 EST The weather bureau's long-term forecast is predicting a drier than normal October to December for much of eastern Australia and north-west Western Australia.