"If you have a bit of cloud about during the day when you have maximum heating from the sun, that energy is not going to get to the surface and it's not going to heat up as much."

Mr Wilke says the high-pressure system is also to blame for Sydney's continual rains, which have been on-again and off-again throughout the week, and will stick around for most of next.

Sydney's CBD was expected to see maximum rainfalls of between 5 and 10 millimetres on Saturday, with a short reprieve of clear skies around lunchtime being undercut by returning falls later in the afternoon.

Showers will remain steady heading into Sunday and Monday, before a changing weather pattern brings the storm before the calm later in the week.

"For Sydney there's no real significant changes to the amount of rainfall we will get [on Sunday and Monday]. We are expecting a bit less rain on Tuesday before we have another front on Wednesday that will bring more showers," Mr Wilke said.

"It looks like Thursday and Friday's conditions will be better. Friday will probably be the next totally nice day."

Rural areas that have remained mostly dry throughout this month will get a good lashing at the start of the week, with falls of up to 15 millimetres predicted in Wagga Wagga on Tuesday, and Dubbo expecting to see up to 10 millimetres on Wednesday.

NSW's north-eastern suburbs will continue to feel the brunt of the falls from Saturday through to Tuesday, with about 30 millimetres of rain forecast for each day.

Mr Wilke said that there was a chance some suburbs in the region could even get up to 100 millimetres of rain, and a "flood watch" warning was still in place for the Northern Rivers region.

"The areas forecasted to get the highest amount of rainfall are those close to the Queensland border, so places like Tweed Heads and Lismore," he said.

The rain will back off to about 10 millimetres in the region on Wednesday, when the trough starts heading off the NSW coast and out to sea.

Next Saturday in Sydney's CBD is expected to be dry, with temperatures climbing about to about 27 degrees.