Sweltering Sydneysiders will have to wait until after midnight for a southerly change to cool large parts of the city.

Summer arrived with a vengeance on Tuesday, as temperatures soared to 38 degrees from Sydney Airport to Campbelltown. Penrith, where the mercury rose to 40.5 degrees, was the warmest place in NSW.

But relief in the form of a cool change is not expected until after midnight for most of the city.

Surfers swarm on Bondi Beach for the first day of summer, as temperatures hit 38 degrees. Photo: Dallas Kilponen

"That means temperatures may well stay warm throughout the evening," said Weatherzone meteorologist Craig McIntosh. "Not so much on the coast, as a strengthening north-easter is pulling it down around there."

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When it does finally arrive, the southerly will usher in a few days of cooler conditions. The Bureau of Meteorology is forecasting maximums of 23 or 24 degrees for the remainder of the working week, before warming up again on Saturday. Wednesday will be partly cloudy with the possibility of very light rainfall, according to the Bureau.

Winds kept temperatures at Observatory Hill more mild than the rest of the city on Tuesday, with the maximum recording of 33.3 degrees taking place at 11.15am. That was still far in excess of the December average of 25 degrees, Mr McIntosh said.

David B braves the midday heat to bring some heat on to the court at Victoria Park. Photo: Cole Bennetts

Firefighters were also attending a grass fire in Londonderry, a suburb in Sydney's north-west, on Tuesday afternoon. The fire flared up at the site of an old hazard reduction burn, but was under control and posed no threat to property, the NSW Rural Fire Service said.

Last month Sydney sweltered through its second-hottest November day ever, and meteorologists globally believe 2015 will be the warmest year on record.

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