Wind speeds of up to 90 km/h are ripping through Melbourne's CBD, and areas near Melbourne Airport, Laverton and Essendon.
The Bureau of Meteorology says severe storms are coming down from the north and west of the state, and winds may reach up to 100 km/h in the next few hours.
There is a severe thunderstorm warning for the entire Melbourne metropolitan area, along with Mildura, Horsham, Warrnambool, Ballarat, Bendigo, Seymour, Maryborough and Geelong.
Strong winds are expected to reach Melbourne's eastern suburbs by about 8pm Monday.
The sudden winds are a fitting end to a spring where temperatures fluctuated dramatically.
A Melbourne Airport spokeswoman said planes were not yet being diverted, but flights could end up being disrupted later this evening is weather conditions worsened.
She advised anyone booked to fly out of Melbourne to assume their flights would still be going ahead as planned.
But Bureau of Meteorology forecaster Scott Williams said while temperatures were typically up and down for that time of year, a lack of rain was particularly notable. Rainfall was about 50 per cent lower than average for spring across the state - making it the sixth driest spring on record for Victoria.
"It certainly looks like it's been a significantly warmer spring than average and also quite dry," Mr Williams said. "That's exactly what you'd expect for the strong El Niño system that we're in."
October temperatures were well above average for Victoria, with six days topping 30 degrees - matching the state's current record. "October was the warmest on record across most of the country," he said.
November was also warm, finishing with Mondays's expected top of 31 degrees in Melbourne. At about 2.45pm the mercury had reached 30.4 degrees, ahead of a cool change forecast to hit Melbourne around 9pm.
The first day of summer will kick off in cooler style with a predicted top of 23 degrees.
Meanwhile in Melbourne, the temperature should dip to 18 degrees on Wednesday, before temperatures rise back up to an expected top of 31 by the weekend.
"We'll still be jumping around quite a lot in temperatures," Mr Williams said.
At this stage, December looks like being hotter and drier than average, with plenty of variation set to continue until the second half of summer arrives, he said.
