Winter doonas were kicked off as the mercury dipped to a low of 17.3 degrees at 5.32am today, a remarkable 11 degrees warmer than the average August minimum temperature in Melbourne.

In fact, last night's balmy conditions were three degrees warmer than the average overnight temperature in the city at the height of summer. January's average overnight temperature in Melbourne is 14.3 degrees.

Bureau of Meteorology senior forecaster Scott Williams said the previous hottest August night was recorded on August 20 in 1885, when Melbourne dropped to a low of 16.2 degrees.

Mr Williams said warm air from central Australia was buffeting Victoria, and last night's cloud cover created ideal conditions for a record-breaking night.

Blustery winds averaging up to 50 km/h are forecast in the city this morning, decreasing to less than 35 km/h during the afternoon.

"We've had a very high temperature in the day and then we've had a windy, cloudy night to follow it and no rain so that's the reason we've stayed exceptionally warm," Mr Williams said.

"The cloud cover acts as a blanket, prevents the ground cooling and of course the wind stirring things up keeps it warmer than if it's still."

At 7.45am today, the temperature in the city was already nudging 19 degrees, with a forecast maximum of 21 degrees today.

Other parts of Victoria are expected to hit the mid 20s today. Mildura is forecast to be the state's hottest location at 25 degrees, while Kerang, Swan Hill and Orbost are expected to reach 24 degrees.

Mr Williams said the three-day warm spell was caused by north-westerly winds driven by a high pressure system over the Tasman Sea.

However the record warm start to August will grind to a halt this afternoon when the first part of a cold change moves across the state.

"It will be a two-part change,' Mr Williams said.

"There's a little bit of rain that will come along later on today, and then there's a more significant band of rain that will come through during tomorrow. It still won't be cold by any means tonight. We're expecting a low of 13 which is still well above the average, and then we will see a top of about 17 tomorrow before that rain sets in. It will probably commence late morning and then run through the afternoon."