The Hunter has sweltered through a day of extreme heat, but a southerly change is due this evening.
The Hunter's hottest temperature was recorded at Tocal, where the mercury rose to 42.2 degrees.
Nobbys hit a high of 38.9 degrees at 1.08pm, rising from a low of 18 degrees at 5.56am.
Williamtown hit a high of 41.1 degrees at 1.35pm, with a low of 14.5 degrees recorded at 5.27am.
Scone hit a high of 41.3 degrees at 2.26pm, up from 16.2 degrees at 5.46am.
Don White, of Weatherwatch, said December days above 40 degrees were not common in Newcastle.
Mr White said this evening's southerly change would lead to milder weather on Friday.
"We're looking at temperatures into the high 30s again on Saturday before a south-easterly develops for a few days. That should keep temperatures down to the mid to high 20s through to Christmas Day," he said.
Air quality was rated hazardous in Newcastle on Thursday, as strong north-westerly winds brought bushfire smoke that obscured visibility.
