Workers will face a tough choice – head early to the beach or stay longer in their air-conditioned offices to dodge the worst of Friday's scorching heat.
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Wollongong is heading for a top of 36 degrees on Friday, and it will be even hotter at Albion Park with 37 degrees predicted.
The entire Illawarra is set for 30+ degrees.
Temperatures in Sydney soared neared 34 degrees by 10am and are forecast to reach 38 degrees, potentially Sydney's hottest day in 22 months.
To the west, Parramatta can expect 39 degrees and Penrith 40 degrees, as north-westerlies draw in heat from baked inland regions. Penrith reached 37.8 degrees by 11am.
"It's going to be a great beach day," said Rob Sharpe, a meteorologist with Weatherzone.
"We won't see a proper cool change until the early evening."
While the eastern suburbs will start to get cooler sea breezes from early afternoon, the sudden drop in temperatures won't come until about 7-8pm, Mr Sharpe said.
Residents in the west, though, won't see the mercury drop until a bit later and then more gradually than those in the east.
"If you want to avoid being in the heat, I'd stay in the office longer," he said.
The burst of heat and expected gusty winds have also triggered a total fire ban for the state, with fire-danger ratings declared "severe".
Similar conditions apply for the Greater Hunter, upper central west plains, north-western and central ranges, the Rural Fire Service said.
More than 25 fires are burning across NSW.
Friday's scorcher will be repeated on Sunday, although the CBD will be spared the worst, with a top of 35 degrees forecast by the Bureau of Meteorology. Saturday will be a milder 27 degrees.
In between, the overnight temperatures may remain above 20 degrees across most of the city until Wednesday.
"Because of that heat, houses are going to get hotter and hotter," Mr Sharpe said. "Sunday is going to be a very painful day for many."
Heat records
A top of 38 degrees for Sydney would make it the city's hottest day since January 18, 2013. That day the mercury reached 45.8 degrees, the warmest in records going back to 1859, the bureau said.
The hottest November day for Sydney was in 1982, on November 25 of that year, when the maximum reached 41.8 degrees.
Warm spells are becoming more likely than cold ones, globally but also in Australia, as the planet warms up because of climate change, scientists say.
According to the bureau's State of the Climate 2014 report, over the past 15 years, the frequency of warm months has risen five-fold compared with a 1951-1980 baseline, while the frequency of cold months has dropped by about one-third.
Overnight, the US National Ocean and Atmospheric Administration declared last month to be the hottest October on record, continuing a series of unusually hot months.
The first 10 months of 2014 are now the warmest such period on record. Should November and December be the 10th warmest on record, this year will be the hottest calendar year, eclipsing 2005 and 2010, NOAA said.
Abnormally warm seas are driving the data towards records highs, including in the Pacific where near-El Nino conditions persist.
Since El Ninos typically bring hotter- and drier-than-usual conditions for eastern and southern Australia, much of the country may endure a hot few months ahead.
"Summer is shaping up to be a hot one - and we're not even at the start yet," Weatherzone's Mr Sharpe said.
Weatherzone is owned by Fairfax Media, publisher of this website.
SMH
