Sydney sweltered through another 30-plus degree day on Saturday with no respite in sight from heatwave conditions until the new year.

Penrith recorded a temperature of 38 degrees just before 2pm on Saturday and the CBD 30, with temperatures expected to be even hotter on Sunday, Weatherzone forecaster Graeme Britton said.

"We are looking at a pretty much repeat performance [on Sunday] - if anything it could be even hotter in the CBD," Mr Britton said.

Sunday is tipped to reach 32 degrees on Sunday with a low of only 23 overnight.