Bureau of Meteorology duty forecaster Richard Carlyon said the warm temperatures, expected to continue until Sunday with a forecast top of 21, were uncommon for this time of year.

"It's been an unusual weather pattern for late August. We've had a very strong high pressure system in the south, over the Tasman Sea, extend a ridge of high pressure across Victoria, blocking cold fronts from coming through," Mr Carlyon said.

"Usually we're affected by more cold fronts, but we've had light winds, clear skies and temperatures slowly building."

But, it's not time to put away the winter woolies yet.

As spring officially arrives on Monday, so too will cooler temperatures.

"The high pressure system which has been blocking other fronts will move away to the east towards New Zealand, so we'll see more frequent cold fronts coming through and cooler weather," Mr Carlyon said.

"On Monday, the first cold front will move through and instead of seeing 20s on the forecast we'll be seeing temperatures back in the mid-teens."

Minor rainfall is also due across the region towards the start of next week.

"We're forecasting isolated showers, most of it in southern and mountain areas, but Bendigo is likely to see a shower or two on some of those days," he said.

Bendigo is expected to reach a top of 17 degrees on Monday with a medium chance of showers.

Tuesday and Wednesday will be a little cooler with maximum temperatures of 14 and a chilly start to the middle of the week with a 2-degree minimum forecast for Wednesday.

Mr Carlyon said the early warm weather was likely to push the average temperature for August to up to about 15.5 degrees, one degree above the monthly average.

"We're trending just above average at the moment, but the last four days of the month will push that average above 15," he said.

"It looks like the average was closer to 12 or 13 degrees for the first half of the month, while the average for the second half of the month looks more like 17 degrees."