The mercury in the city will climb to 38 degrees on Friday, according to updated forecasts from the Bureau of Meteorology, after reaching about 27 degrees on Thursday.

Many western suburbs sweltered in temperatures well above 30 degrees on Thursday, with 35 degrees reached in Bankstown and 37 in Penrith.

Residents, particularly in the west, will feel as if they are in the middle of summer from Thursday until Monday.

Parramatta can expect a top of 39 degrees on Friday with Penrith likely to reach 40 degrees, the bureau said.

"It's pretty significant [heat] for November, that's for sure," Rob Sharpe, a meteorologist at Weatherzone, said.

Saturday will be cooler before temperatures again climb to 35 degrees in Sydney's CBD on Sunday and 40 degrees or higher in the city's west.

Richmond, to Sydney's north-west, can expect 42 degrees on Sunday, a temperature reached only twice in 75 years of records for the town during November, according to the Bureau of Meteorology.

Early summer

Many parts of inland Australia "have been getting their summer weather in November" after a series of heatwaves sweep across the continent, Mr Sharpe said.

Alice Springs, for instance, may register its fifth day of 40 degrees or warmer this November by Friday, including a record-shattering 44.9 degrees recorded a week ago.

That sizzler set a new high for November and beat any top recorded for December.

The unusually warm spring and the bureau's forecast for more to come has prompted the Bushfire & Natural Hazards CRC to update its seasonal bushfire outlook. It now expects most of the populated regions of south-eastern Australia to have an "above normal" bushfire season.

Heatwave view

A heatwave projection service provided by the weather bureau projects a three-day heatwave from Friday stretching from north-eastern Victoria all the way to Darwin, covering almost all the regions to the east.

For towns such as Bathurst, west of the Blue Mountains, the coming burst of heat is likely to be the sixth heatwave since the start of October. That gauge is based on at least three days in a row during which the maximums are in the top 10 per cent of records for those days, according to the Scorcher website produced at the University of NSW.

Mr Sharpe said the third of the troughs due to move through Sydney by next Monday is relatively powerful and should bring some much-needed rain as well as cooler conditions. The bureau is predicting as much as 10mm of rain for the CBD on Monday.

"The pattern [of heatwaves] will at least briefly end," he said.

"We'll have a bit of a reprieve," Mr Sharpe said, adding that the intense heat is likely to transfer from north-eastern Australia to the country's north-west.

This week, the weather bureau raised its forecast for an El Nino being declared in the Pacific. The weather event, which typically leads to higher than usual temperatures and lower rainfall for eastern and southern Australia, now has at least a 70 per cent chance of occurring over the summer, the bureau said.

Even near-El Nino conditions are enough to raise the odds of abnormal heat and dry conditions for regions stretching from Australia to Malaysia, and are boosting global temperatures already elevated by background climate change, climatologists say.

Last month was the hottest October in more than 120 years of records, the Japan Meteorological Agency said last week.

US agencies say the April-September period were also the hottest, making it more likely that 2014 will challenge 2005 and 2010 as the hottest year on record.

Weatherzone is owned by Fairfax Media, publisher of this website.