Sydney has clocked its hottest December day in 11 years as north-westerly winds from the hot interior kept sea breezes at bay.
Fire crews, meanwhile, are battling two blazes with residents near Abermain in the Hunter with home at risk. The Rural Fire Service has issued an emergency warning for the area.
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Sydney weather: the heat is on
The entire Sydney basin will see temperatures climb towards 40 degrees on Tuesday and Wednesday with little temperature drop overnight.
The city's temperature reached 37.8 degrees - or almost two degrees more than forecast - just after 1pm. So far the hottest inland site has been Richmond with 38.8 degrees recorded a few minutes earlier.
Miranda Langton, a meteorologist at the Bureau of Meteorology, said light sea breezes were gathering off the coast. Those managed to knock the mercury down 6 degrees in half an hour from the peak before temperatures started rising again.
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Tuesday's warmer-than-tipped maximum has prompted the bureau to raise its forecast for the overnight minimum to come in at 26 degrees.
Sydney's record high minimum temperature for December is 26.3 degrees, set in on Christmas Day,1868.
"There is a good chance we could break that," Ms Langton said.Â
Jacob Cronje, a senior meteorologist at Weatherzone, said it still possible to see some further heating in inland regions.
"It's a very hot air mass," Mr Cronje said. "We could see some 40s", with Bankstown being one site Weatherzone had earlier tipped to reach that mark.
Much of south-eastern Australia is covered by the hot spell. All four capitals - Canberra, Melbourne, Adelaide and Sydney - reached at least 33 degrees on the same day for the first time in December since 1965, Weatherzone said.
Heat lingers
Sydney's warm night is expected to be followed by another hot day, with 38Â degrees forecast for the city and 38 degrees for the west.
The Rural Fire Service has issued a total fire ban for the Sydney metro and Illawarra/Shoalhaven regions for Wednesday. Both regions are rated as having "severe" fire danger.
Other regions with total fire bans on Wednesday are in the upper central and lower central west plains.Â
The cool change is still expected to reach Sydney around dinner time, Mr Cronje said.
The most recent warmer December day for Sydney was 39 degrees on 7 December 2005, the bureau said.
On average there are fewer than one day of 35 degrees or warmer weather in Sydney. The most recent year with three such days was in 2000. On current forecasts, tomorrow will make it three for this month.
Health, fire risks
St Vincent's Hospital and the CIty of Sydney launched their extreme heat protocol to assist the inner-city homeless over Tuesday and Wednesday.Â
The hospital's Homeless Health Team have been patrolling handing out water, sunscreen, and information about heat illness and where the homeless can find some shade.Â
Standard temporary accommodation will be available to anyone who contacts Link2home over the two days, St VIncent's said.Â
The Rural Fire Service has issued an emergency warning for resident at Abermain near Cessnock in the Hunter Valley.
#Abermain / #Neath Fire: It is too late to leave for residents in Carrs Rd, Charles Rd & York St. Seek shelter as the fire approaches.
— NSW RFS (@NSWRFS) December 13, 2016
The RFS is also deploying its very large water-bombing air tanker to help fire crews on the ground.
Fire danger ratings for most of NSW are "very high" or "severe".Â
The Riverina town of Hay is the state's hottest site, with 40.1 degrees.
With the lingering heat, the Bureau of Meteorology said the strip of coastal NSW will have a low-intensity heatwave for Tuesday to Thursday. (See chart below.)
With Kate Aubusson
Follow Peter Hannam on Twitter and Facebook.
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