"Normally there's a big difference between the CBD and western Sydney because of the sea breeze, but the north-westerly winds are expected to be so strong on Sunday that there will be no sea breeze felt anywhere," Ms Miskelly said.
Such high temperatures in March would not break any records, but they are pretty rare, Ms Miskelly said.
"Sydney has only reached 38 degrees in March eight times in 159 years of records, so it's definitely unusual" Ms Miskelly said.
"But it would be the hottest day for this late in March [instead of early March]."
The high temperatures, combined with winds predicted between 30-50km/h, are expected to pose difficult conditions for emergency services.
NSW Rural Fire service has issued a total fire ban on Sunday affecting more than half of the state, including the Greater Sydney Region, Greater Hunter, Illawarra/Shoalhaven, Far South Coast, Monaro Alpine, Southern Ranges, Central Ranges, North Western, Lower Central West Plains, Southern Slopes and Eastern Riverina regions.
"We've had a very long period of hot dry weather, and we are still in the official bushfire danger period, which runs until the end of March," said Greg Allan, spokesman for NSW Rural Fire Service.
"Unfortunately the rain recently hasn't been enough to soak in and really make any difference.
"So we're asking people to remain vigilant."
While Sydneysiders can expect a cool southerly change sweeping across the city after sunset on Sunday evening, temperatures will remain hot on Monday, sitting around 30 degrees.
A second push of cooler air is expected to pass through the city around Tuesday and Wednesday, bringing with it cooler temperatures and high chances of rain for the rest of the week, according to Weatherzone.
Weatherzone is owned by Fairfax Media, publisher of this website.
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