Sydney's wettest October in nine years helped ease fire conditions but the coming surge in heat will sap much of those gains in vegetation moisture, the Rural Fire Service and meteorologists say.

Observatory Hill, on the edge of the CBD, collected 167.6 millimetres of rain in October, twice the average. Rain on 17 days almost meant Sydney had its cloudiest October in more than 40 years, according to Weatherzone.

There is no sign of early rainfall relief for farmers and firefighters with a drier and warmer than average forecast for most of spring for eastern Australia. Credit:Wolter Peeters

That wet spell, though, is fast fading, with November set for a warm start. After a top of 27 degrees on Thursday, the mercury in Sydney will climb to 37 on Friday before another warm day of 30 on Saturday, the Bureau of Meteorology predicting.

The first bout of heat "is a bit of a shock to everybody", Kim Westcott, a meteorologist at Weatherzone, said, especially as it comes after "three weeks of carrying the umbrella around".