Sydney's run of unusually warm and sunny days will last well into next week as dominant high pressure systems block a series of cold fronts streaming across the country's south.

The Harbour City can expect daytime temperatures 3-7 degrees above the August norm of about 18 degrees over the coming week, the Bureau of Meteorology said.

More beach-welcoming weather on the way for Sydney. Credit:James Brickwood

The agency, though, backed off an earlier prediction that Sydney could get a top of 28 degrees next Wednesday and now rates 25 degrees the more likely maximum. Friday's top will be 23 degrees before conditions cool slightly for the weekend.

"A dominant high pressure system is sitting near Brisbane, and we're going to see a series of fronts, one after the other, each dropping south" of Sydney, Rob Sharpe, a meteorologist at Weatherzone said.