Sydney's scorching weather is set to continue on Monday, with temperatures forecast to surge beyond 31 degrees and the chance of a thunderstorm developing during the day.
In Sydney's western suburbs, temperatures are expected to hit the mid-30's, eclipsing Sunday's high of 36 degrees, said Jane Golding, a meteorologist at the Bureau of Meteorology.
It is a familiar story across the state.
Over the weekend towns in north-western NSW experienced their first 40-degree day for spring this year, with Wilcannia and White Cliffs reaching 42 degrees, while Tibooburra had its hottest week in at least 100 years.
In Sydney the warm weather was well above this month's average maximum temperature of 23.5 degrees, itself 1.4 degrees warmer than the long-term average. Sydney's warmest day this month remains the 33.8 degrees set on October 5, the hottest NRL grand final day in history, while Sunday saw the mercury climb to 32.5 degrees.
The rest of the week should be mostly dry for the city, the bureau said.
Tuesday is expected to reach a maximum of 28 degrees, before cooling on Wednesday to a top of 23 degrees.
But it will steadily heat up again, to 26 degrees on Thursday and 27 degrees on Friday, before reaching a forecast high of 32 degrees on Saturday.
Weatherzone has predicted an "extreme" pollen reading in Sydney on Monday.
Fire danger
With extensive heat again expected across the state on Monday, the Bureau of Meteorology has issued a fire weather warning for seven fire regions: Far North Coast, North Coast, Greater Hunter, New England, Northern Slopes, North Western and Upper Central West Plains.
All seven areas have had been declared total fire ban regions, ahead of a "vigorous trough", bringing with it hot, dry and very windy conditions, the bureau said. "Dry thunderstorms are possible over much of state in the vicinity of the trough."
The bureau has also issued fire weather warnings for parts of South Australia, Western Australia and Queensland.
Mandora in WA reached 43.6 degrees on Sunday, while Moomba Airport in SA reached 43.1 degrees and Birdsville in Queensland hit 43.3 degrees.
Global warmth
Another unseasonably warm spring weather follows a global pattern.
The 12 months to September has already been the warmest such period since records began in 1880, the US National Oceanic and Atmospheric Administration (NOAA) said last week. NASA which uses a different measurement system concurred with NOAA's findings.
Temperatures have risen 0.69 degrees above average, eclipsing the three previous September to August ranges, the last of which was set last year.
"It's pretty likely" that 2014 will break the record for hottest year, NOAA climate scientist Jessica Blunden said in a statement.
The global heat wave stretches back for the past 355 months, all of which have been hotter than the long-term average.
"Every month on this planet has been warmer than the 20th century average," said Ms Blunden.
What is unusual about this years potential to break the temperature record is that it will not be a "super El Nino" year, where sea temperatures in the equatorial Pacific rise significantly above average.
The last super El Nino ended in 1998, the hottest year ever recorded - a year frequently cited by climate change skeptics who claim that the planet has not warmed in 18 years.
El Nino chance
The Bureau of Meteorology said last week that an El Nino had a 50 per cent chance of developing this year.
Andrew Watkins, the Bureau of meteorology's manager of climate prediction services told Fairfax Media that records could be broken even without a "full-blown El Nino" because of the planet's broad scale warming.
The Bureau warned that hot and dry conditions are expected, prompting bushfire warnings.
"We are expecting a warmer than average summer for the next three months," said Ms Golding.
A spokesman from Weatherzone said Sydneysiders should not be complacent about the threat of fires despite the heavy rainfall experienced in storms earlier this month.
"Sydney as a whole has done quite alright in terms of rainfall this month," the spokesperson said. "We've exceeded our average monthly total in terms of rain already, but we can't become complacent when we start bushfire season."
With Megan Levy
Weatherzone is owned by Fairfax Media, publisher of this website.