Sydney's late-season heatwave fell short of delivering the city's hottest trio of March days since 1902, with another burst of warmth coming next weekend.

Monday's forecast top of 30 degrees by the Bureau of Meteorology turned out to be on the high side for Observatory Hill - though parts of the city's west tipped over 35 degrees.

Sunday's 38.4-degree-high, recorded at Observatory Hill, was the hottest this late in March since 1940, while Saturday's top reached 31.9 degrees, Brett Dutschke, senior meteorologist at Weatherzone, said.

The city has had only two previous stints of three 30-degree days in a row in March - in 1889 and 1902 - he said.