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A frontal system moving through the state on Wednesday and again on the weekend will draw heat in from central Australia. While winds will pick up, there will be little rain associated with the fronts.

"There could be the odd shower [such as late on Sunday] but it will probably just be dry all the way through" into next week," Mr Hough said.

Fire risks rise

While the winds are not expected to be very blustery, the combination of lower humidity and higher temperatures will also push up fire danger ratings from Wednesday.

"Over the next few days, we'll start to see more 'very high' fire danger ratings," Ben Shepherd, a senior spokesman for the NSW Rural Fire Service said.

For the Sydney region, the ratings are not likely to approach the level required to trigger a total fire ban during the current warm spell, he said.

The areas of "very high" ratings for Wednesday include Sydney and the Illawarra/Shoalhaven regions.

"That bit of rainfall we had was just enough to take the edge off [the fire risks]," Inspector Shepherd said.

The 20 millimetres of rain collected at Observatory Hill on September 8th was the most in a day in about 10 weeks.

Even so, evaporation rates so far this month are running slightly above the rainfall, continuing the process of drying out that has fire authorities predicting an early and active fire season along most of the east coast of Australia.

Recent rainfall had also been patchy. Places such as Katoomba in the Blue Mountains have fared relatively well, with the 67 millimetres of rain so far in September the best monthly return since March.

Richmond, on Sydney's north-west fringe, largely missed out on the decent falls, Inspector Shepherd said.

The inland warmth and winds have also nudged temperatures above 30 degrees on Tuesday in far-western NSW towns such as Wilcannia, while Mildura in Victoria's north-west corner reached 29.9 degrees.

Conditions were also whipping up large dust clouds west of Broken Hill that were visible on satellite images.

El Nino update

Separately, the bureau has left its estimate of the chance of an El Nino forming in the Pacific later this year at 50 per cent in its latest update. That's about twice the normal risk.

"Most international climate models surveyed by the bureau indicate that the tropical Pacific is likely to warm to El Nino thresholds by the end of spring," it said.