Victoria could see its first 40ºC so far this summer on Monday as Melbourne sweats through its hottest day in a year.

A tongue of hot air from central Australia will sweep across Victoria on Monday ahead of an approaching cold front.

Image: Hot air over Victoria on Monday afternoon, according to the ACCESS-C model.

Amid this hot air mass, the temperature in Melbourne was already above 30ºC by 9:30am. At midday, it had reached 34ºC and is expected to top out at around 38ºC this afternoon.

While this is likely to be the hottest day in a year for Melbourne, and a whopping 12ºC above average for this time of year, it's not out of the ordinary to see days this hot in the middle of summer.

In records dating back to 1856, Melbourne has registered over 120 days at or above 40ºC during January. That's an average of roughly seven to eight per decade.

But while today's warmth isn't out of the ordinary historically, it will be noticeable across the city. Prior to this week, Melbourne's highest temperature so far this summer was only 33.7ºC, which occurred in the middle of December.

Daytime heat in Victoria has been suppressed this summer thanks in part to the cooling effect of La Niña on summer-time air masses over Australia.

Victoria as a whole just registered its coolest December in a decade based on daytime maximum temperatures. For Melbourne, it was the coolest December in 19 years.

Outside Melbourne, the mercury could reach 40ºC in northwest Victoria this afternoon. If it does get this hot, it will be the first 40ºC day in Victoria so far this summer. Impressively, this would be Victoria's latest first 40ºC of summer since 2008/09.