Region can expect a 28-degree day with Sydney's first burst of spring heat

Very high fire danger is forecast on what should be a very warm and windy Wednesday across St George and Sutherland Shire.

Maximum temperatures of 28 degrees are expected across the region.

At 8.30am, it was already 17 degrees in Lucas Heights and 21.8 degrees at Sydney Airport.

Temperatures are likely to back off along the coast on Thursday and Friday before climbing back to the high 20s on Saturday. 

"It could be touch and go" whether 30 degree totals are reached in coming days, Tom Hough, a meteorologist with Weatherzone, said.

"Certainly, we'll get the high 20s."

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.

The region can expect a mostly sunny morning on Wednesday.

There’s the chance of a thunderstorm with little or no rainfall during the afternoon or evening, according to the Bureau of Meteorology. 

The NSW Rural Fire Service (RFS) said the warm and windy weather will increase the risk of fire.

The RFS has issued a "very high" fire rating for the Greater Sydney Region.

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.