Melbourne is set for an "insufferable" weekend, particularly on Sunday, as a combination of high temperatures and rising humidity lift heat stress to levels rarely seen in the city.

According to the Bureau of Meteorology, humid conditions will make the maximums for Friday though to Sunday feel considerably warmer than the temperatures suggest.

The current forecasts are for tops of 29 and 33 for the city on Friday and Saturday. On Sunday, the city can expect a scorching 39 degrees, with some suburbs possibly climbing into the low-40s

"I wouldn't want to be playing the men's tennis final on Sunday," said Chris Godfred, a senior bureau forecaster, referring to the Australian Open event. "It won't be very pleasant."