Weather records have been smashed in Western Australia as a trough moves across the state, bringing more unseasonal heat to the country’s east.

Parts of WA have already broken the 40-degree mark as 19 records tumbled on Wednesday.

“More are expected to be broken today … [and there will be] more record temperatures in the Goldfields on Friday,” the weather bureau tweeted on Thursday.

The warm spring weather is expected to arrive in the eastern states in time for this weekend’s AFL and NRL grand finals.

Senior meteorologist Angus Hines said Melbourne could expect warm and sunny conditions for the AFL decider on Saturday, “with a maximum temperature into the high 20s for the opening bounce”.

“We could see a few patches of cloud throughout the afternoon, but conditions are expected to be mostly bright and sunny,” he said.

“The clear conditions are due to a high-pressure system across Victoria this week, with winds turning north to north-westerly on Saturday and bringing the warmer weather.

“While not as warm, temperatures will be reaching the mid-20s tomorrow afternoon, and clear skies are forecast for the grand final parade and Victorian public holiday.”

If the forecast eventuates, it will be just the fifth AFL grand final played in Melbourne on a day reaching 26 degrees or warmer.

Tweet from @BOM_WA

Sunday’s NRL grand final clash at Sydney Olympic Park is also expected to be played in very warm conditions – although the night-time kick-off will bring some relief.

“Maximum temperatures are expected to reach the mid-30s in western Sydney on Sunday afternoon, as hot, gusty north-westerly winds flow into the Sydney basin,” Hines said.

“By kick-off at 7.30pm (AEST), temperatures are still expected to remain in the high 20s and decrease steadily throughout the game, though overhead conditions will remain mostly clear, with just a few patches of cloud.”

Earlier games, including the NRLW grand final, will be played in peak heat. Temperatures as high as 35 degrees are likely.

“Those hot north-westerly airstreams are forecast to make way for a brief, cool southerly change early on Monday in time for the NSW public holiday,” Hines said.

If temperatures reach 35, it will be the hottest NRL grand final day since observations began at Sydney Olympic Park.

And temperatures are tipped to get even hotter in Sydney next week. Forecaster Weatherzone said highs of 37-38 degrees were expected in the city’s west on Tuesday.

The grand final weekend heatwave comes two weeks after spring arrived with another burst of unseasonal heat in the eastern states, bringing health warnings and catastrophic fire danger.

Last week, the BOM declared an El Niño event for the coming summer.

“The declaration of these events, and their concurrence over spring, reinforces the bureau’s long-range rainfall and temperature forecasts, which continue to predict warmer and drier conditions for much of Australia over the next three months,” it said.

“The confirmation of an established El Niño increases the likelihood that the event will be sustained through the summer period.”

The bureau’s most recent long-range forecast predicts that, from October to December, most of Australia is three times more likely than usual to experience “unusually high maximum temperatures”.