Sydney has sweltered through a scorcher but Santa is bringing a change with him for Christmas Day which is set to be much cooler than Christmas Eve.

The family barbecue is likely to be held under cloudy skies with a maximum of 23 degrees predicted and a south-easterly wind reaching 25km/h.

The Christmas barbecue is likely to be held under cloudy skies. Credit:Jessica Hromas

The cool change comes after Sydney's Observatory Hill reached 37.7 degrees just after 2pm on Sunday, well shy of Penrith's maximum of 42.1 degrees.

The western Sydney suburb came close to breaking a record set just 10 days ago when it reached 43.5 degrees.