Sydneysiders are being bathed by late-season warmth, the warmest for this late in autumn in 28 years, with the city exceeding 29 degrees at lunchtime.

The city reached 29.6 degrees, 8 degrees above the late-April average and half a degree warmer than May 5, 2012.

The last time Sydney has been warmer later in the season was in 1986 when the city reached 29.7 degrees on Anzac Day.

Residents are making the most of the conditions by flocking to parks and beaches in numbers not seen at this time of year in decades.

North-westerly winds have been dragging very warm air from western New South Wales where heat has built due to a lengthy run of northerly winds under clear skies. Western NSW has been reaching the low-to-mid 30s.

The warm weather will not last long with a gusty southerly change this evening cooling the city by 7-10 degrees.

Anzac Day will warm up to only 21 or 22 degrees across the city with southerly winds bringing cloud and a few showers.

Looking further ahead, there is some good news for those who like the warm days.

Residents can plan for temperatures in the mid-20s on Saturday and Tuesday, just ahead of a cooler change.

Elsewhere in NSW, today is also the warmest for this late in the season in 28 years in Newcastle, reaching 30 degrees.

It hasn't been this warm this late in the season in 12 years in Bourke (32 degrees), Kempsey (31 degrees) and Merimbula (26 degrees), nine years in Coonamble (31 degrees) and seven years in Port Macquarie (29 degrees) Lismore (30 degrees) and Casino (30 degrees).

Brett Dutschke is a senior meteorologist at Weatherzone, which is owned by Fairfax Media, publisher of this website.