The Bureau of Meteorology has revised its warnings and says severe thunderstorms are no longer affecting Sydney's fringes.
A warning remains in place for parts of the North West Slopes and Plains district, including Moree, Narrabri, Mungindi and Collarenebri.
An earlier warning said severe thunderstorm with large hailstones, heavy rainfall and flash flooding could strike the Blue Mountains and Hawkesbury areas of Sydney.
Sydney's near-perfect summer has extended well into autumn, with the city notching up a record run of warm days for the season.
With Wednesday's peak of 27.8 degrees, Sydney has now clocked daily maximums of at least 25 degrees for the past 17 days, eclipsing the previous record of 16 such days set in 1977, said Brett Dutschke, senior meteorologist with Weatherzone.
A cool change later on Wednesday should moderate conditions slightly. Even so, with 26-28 degrees expected each day until Monday, according to the latest forecasts, the record spell could reach 22 days.
“In March, you'd normally start to get the odd decent front or two coming through,” Dr Dutschke said. “They just haven't made it as far north as Sydney.”
The city has also been bathed in a daily average of seven hours and 40 minutes sunshine since the warm spell began on March 3, about 80 minutes more than the long-term average for this time of the year.
The balmy stretch comes after Sydney recorded its driest summer in 27 years. Unlike cities such as Melbourne and Adelaide, Sydney also largely avoided extreme heat with only six days above 30 degrees for December to February and humidity was the lowest in at least a decade, Dr Dutschke said.
While March's rainfall has been Sydney's wettest for any month since November with 63.8 millimetres so far, much of it has fallen in short thunderstorm bursts that have caused only brief interruptions to outdoor activities.
“Generally you just wait for a little while and then you get back into it,” Dr Dutschke said.
More thunderstorms are expected in the next week, though, with most of NSW likely to be affected. Some areas can expect multiple days of storms with hail and strong winds a risk, he said.
So far in March, Sydney's average maximum has been 26.9 degrees, or more than 2 degrees above normal for the month, and ahead of the average during last summer of 26.5.
The warm conditions in March extend far beyond Sydney, with Hobart running about 3 degrees above normal and Melbourne more than 2 degrees above.
“Australia is on target to achieve one of its five warmest Marchs on record,” Dr Dutschke said.
Last year was Australia's hottest in more than a century of records, while Sydney had its hottest year in records going back to 1859. Meteorologists say a background warming because of climate change is making it more likely that temperatures for warmth will be broken, while fewer cold records are falling.