Sydneysiders will be leaving their winter woolies at home on Sunday to welcome what is expected to be the warmest July day on record.

Sunday's forecast of 26.0 degrees creeps above the previous maximum temperature by 0.1 degree to herald the hottest July day in over 27 years.

The current record of 25.9 degrees for the coldest month of the year was set on 24 July 1990.

The minimum predicted temperature for Sunday is 12 degrees for much of the city thanks to a cold front sweeping east across the country, pushing warmer conditions toward the east coast ahead of cooler conditions early next week.

The cold front could bring strong wind gusts across parts of NSW, however Sydney will escape the worst of it, experiencing only above-average temperatures

The high temperature should be fairly uniform throughout the city, said Fairfax Media's Weatherzone meteorologist Kim Westacott.

But the trade-off for the top temperature will be a cloudier day, she said.

"The high cloud coming through will mean Sunday will be more and more cloudy throughout the day. We won't get the beautiful blue skies we got [on Saturday], but it's a pretty good weekend all round," Ms Westacott said.

Showers are forecast for Monday, with an 80 per cent chance of rain between five and 10 millimetres as the maximum temperature dips to 21 degrees.

"We'll see a low pressure trough come through on Monday and that will bring some showers with it," Ms  Westacott said.

"The current forecast is up to eight millimetres, and that will cool things down too."

The mercury is not expected to crack the 20s for the rest of the week, with lows between eight and 10 degrees through to Friday.

"Tuesday and Wednesday we'll get the odd shower, and we'll notice it's gone back to the high teens again. On Thursday and Friday, we'll see some more rain develop as well," Ms Westacott said.

The temperatures, when paired with below-average rainfall, have prompted concerns from the NSW Rural Fire Service (RFS) that this year's fire season could start early.

Speaking to the ABC, NSW RFS Commissioner Shane Fitzsimmons said the landscape has dried up in some areas, with particular concerns for the NSW south coast, northern ranges and central west.

"We could see very much the potential for an early start to the bushfire season in different parts of NSW as we head into this next couple of months," Mr Fitzsimmons said.

Officially, the bushfire season lasts from October 1 to March 31. The last season was described by the RFS as "the worst fire weather conditions ever recorded in NSW", with more than 11,000 fires burning 277,434 hectares and destroying 65 properties.

with Georgina Mitchell