It's the middle of winter but Thursday has felt closer to a summer's day in Sydney, as the mercury climbed 9 degrees above the July average of 16.4.

At a top of 25.2, it's easily the hottest day on record for the first week of July – a full degree above the previous record of 24.1 in 2004.

Sunrise at North Cronulla beach on Thursday. Summer-style temperatures have broken the record for the first week of July. Credit:John Veage

And it will remain relatively warm until a cool wind change on Friday afternoon, although even over the course of the weekend, temperatures will remain around 2 degrees above average.

The monthly temperature record for Sydney's Observatory Hill is 26.5, from July 30 last year.