Maroubra Beach
© Kate Geraghty
Exercising early at Maroubra Beach on Wednesday.
A scorching end to 2016 will ensure Sydney registers its hottest year in more than a century-and-a-half of records.

The mercury is expected to climb to 37 degrees in the city on Thursday and 42 in Penrith, and fall just a couple of degrees shy of that on Friday, according to the Bureau of Meteorology.

All of coastal NSW will endure a heatwave on Thursday, with almost all of it either ranked as severe or extreme. (See bureau chart below). Authorities have also activated the state's heatwave action plan to ensure the public takes care to limit the effects of the heat, such as by staying hydrated and limiting outdoor activity.

The surge of late-December heat means Sydney would notch the city's hottest year in records going back to 1858 "without a doubt", Joel Pippard, a meteorologist with Weatherzone, said. "To not do that, temperatures would have be below zero."

According to Weatherzone, Sydney's maximum temperatures, including Wednesday's top of almost 29 degrees, lifted the average so far this year to 23.76 degrees. That's two degrees above the long run norm, and about a quarter degree higher than the previous hottest year in 2013.

Minimum temperatures will eclipse the previous high set in 2010 by almost half a degree, and are running at an average of just over 15.5 degrees for 2016 with just a couple of days to go, Mr Pippard said.

"It's mainly due to those cold days not being so cold," he said. "Those cold fronts have been dipping south [of Sydney].

Overnight warmth is a feature of the current heatwave, with Sydney's temperatures likely to remain above 23 degrees until at least Tuesday, according to bureau forecasts. With high humidity, it will feel a few degrees warmer than that.
Sydney heawave

Fire risks will increase along with the mercury, with fire danger ratings reaching "high" levels on Thursday for Sydney, the Hunter and north coast regions, and for the central west plains and north western districts, the Rural Fire Service said.

Other agencies issued warnings for the coming heat, particularly as it will coincide with a number of year-end events.

"Festival organisers should ensure that partygoers have access to free drinking water, shade, first aid services, and quiet areas where patrons can relax when they need a break," Michael Gannon, president of the Australian Medical Association, said.

Festival attendees also had a role to play in ensuring their own safety, he said: "Taking illicit substances is illegal and dangerous, and tragically we have seen deaths and hospitalisations at festivals in previous years".

Ben Scalley, NSW Health's Director of Environmental Health, said people should take precautions.

"Heat-related illness is very serious and ranges from mild conditions to very serious medical emergencies," Dr Scalley said. "Heat puts a lot of strain on the body and can cause dehydration, heat exhaustion and heat stroke. It can also make underlying health conditions worse."

Areas where the temperatures could climb above 39 degrees on Thursday include regions from Sydney northwards to Taree, and a broad swathe north-west of Dubbo, stretching into Queensland. (See bureau map below.)
Sydney heatwave
The Bureau of Meteorology is expected to release its annual assessment of temperatures for Sydney, NSW and the rest of Australia next week after the final 2016 figures are collated. This year will be Australia's fifth warmest in records going back to 1910, the ABC reported on Wednesday.