Saturday's sultry top of 30.6 degrees in the city was swiftly followed by cold winds and a forecast temperature of just 18 degrees on Sunday.

Bureau of Meteorology senior forecaster Rod Dixon said Saturday's hot weather was unusual for this time of year and unlikely to be repeated any time soon.

"It hasn't been this warm this early in September before," he said.

As short sleeves and thongs came out of hiding in Melbourne, September records were toppled in the north and east of the state.

Bushfires also broke out in Victoria's east, with the Country Fire Authority issuing a Watch and Act warning for the Dargo, Marlo and Buchan areas.

A State Emergency Service spokesman said they had received 154 requests for assistance in the past 48 hours, the vast majority relating to trees falling in the wind.

Calls were spread right across the state with the Broadmeadows and Bairnsdale units among the busiest.

But a strong southerly change that swept over Victoria late on Saturday will bring cooler conditions for the rest of the week.

"Those temperatures yesterday were at the extreme end of what we can expect in September," Mr Dixon said.

"It's not unusual to have high temperatures, then cool weather to follow, with the land heating up in the north of the state but the oceans still quite cool."

Monday is expected to bring further showers and a top of just 16 degrees, climbing to 17 on Tuesday and peaking at 22 on Wednesday.

Colder conditions and a few showers will hit later in the week, ahead of a mostly dry AFL grand final day and a top of 17 degrees.