Temperatures in Sydney will climb into the 30s in coming days as very warm air from inland Australia gets drawn to the coast, setting up potentially NSW's first 40-degree day recorded in September.
A "vast area" of the state will have very high fire danger by the weekend, with some areas tipping into "severe" risks, Ben Shepherd, a spokesman for the NSW Rural Fire Service, said.
The mercury will begin a steady rise from Wednesday's relatively chilly - though bang on average - forecast top of 20 degrees in the city to 25 degrees by Thursday as the sunshine increases.
By Saturday, Sydney will be looking at a top of 33 degrees but most of inland suburbs will be reaching higher temperatures, including 36 degrees in Penrith, according to the updated Bureau of Meteorology forecasts.
"It's really going to be quite hot in Sydney," Jacob Cronje, senior meteorologist at Weatherzone, said.
The worst of the heat, though, will be felt in the state's north-west, where are a large region is likely to endure 39 degrees or hotter conditions on Saturday.
Wanaaring, which holds the current NSW record for September at 39.6 degrees in 2004, is among the expected hotspots.
NSW has never had a 40-degree day recorded in September, and the latest model runs are putting such a temperature in play, according to the Bureau of Meteorology.
Mr Cronje said that each wave of cold fronts moving across the country at this time of year tends to draw in the hot, dry conditions building over central Australia. So far, there's little sign of a break of that pattern of heat pooling in the red centre.
"I don't think that heat is going anywhere," he said.
Alas for those holding out for rain, there are few signs of more than the odd shower for most parts of NSW over the coming week, including Sydney.
So far Sydney has recorded just 24.4 millimetres of rain since the start of July.
That tally - if not added to by more than 3.7 millimetres by the end of the month - would be the city's second driest July-September period on record, trailing only 1907, Blair Trewin, senior climatologist with the bureau, said.
Saturday's expected maximum temperatures. Source: Bureau of Meteorology
Fire risks to be elevated
Along with the dry conditions and rising temperatures, winds are also likely to strengthen in coming days, Mr Cronje said, adding to the fire risks.
Fire authorities are gearing up for a more active and early fire season.
As of Wednesday, the state had more than 50 fires burning, nine of them uncontained, Inspector Shepherd said.
Sydney has already had its first total fire ban day, with last Wednesday's 33.8 degree maximum the first time the mercury had topped 33 degrees in the city by the first half of September in almost 160 years of records.
While it's too early to say whether the city will have another day of total fire ban during the coming warm patch, Inspector Shepherd said it may only take the increase in forecast wind speeds of a couple of kilometres per hour to nudge Sydney into that category.
As it is, areas of north-west NSW stretching into the Hunter are likely to have severe fire danger ratings for the weekend, he said.
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