A short-lived reprieve from the blistering heat will end today, with today's temperatures in the Hunter expected to top 40 degrees.
The Upper Hunter will bear the brunt of the heatwave, with Singleton likely to peak at 43 degrees before the mercury continues to soar up to 45 degrees tomorrow.
It has prompted the Rural Fire Service to upgrade the Hunter's fire danger warning to severe today.
But RFS Superintendent Paul Jones says the worst may still be ahead.
"If we get the same sort of winds that we had earlier this week with those temperatures, we could even get up into the extreme fire danger behaviour, and possibly even getting close to catastrophic," he said.
"It just depends on how strong the winds are, with temperatures like that it just makes life very difficult for firefighters."
Hunter firefighters are baffled by the lack of fire activity across the region, praising residents for behaving responsibly.
While the rest of the State has battled intense blazes for days, Hunter crews have managed to quickly contain fires that have broken out, including one near Muswellbrook on Wednesday.
Superintendent Jones says the Hunter has been lucky so far.
"The Hunter Valley is one of the most extremely fire prone areas in the state," he said.
"It's extremely unusual for us to be as quiet as what we were, with the weather conditions that we had last week.
"We're very grateful for that but certainly none of the firefighters in the Hunter Valley are taking it easy.
"They're all very much aware of how fire prone the area is."
Felicity Gamble from the Bureau of Meteorology says a shortage of rain is compounding the problem.
"That would normally lessen the strength of the hot air mass," he said.
© ABC 2013
00:03 EST snParts of Sydney and the Blue Mountains have been battered by large hailstones after a severe thunderstorm moved across the area.