Revised forecasts are tipping an even sweatier end to this week, with Melbourne set to swelter through what could be its hottest run of days in 100 years.

The Bureau of Meteorology this afternoon increased its heatwave predictions for the week, with the mercury expected to hit 38 degrees tomorrow before climbing skywards to 40 and above until Saturday.

James Bedurke, Emma Patane, Dina Wardell and Mary Tseros take a dip to cool off in the 37-degree heat at Altona Beach on January 13. Credit:Paul Rovere

The forecast looks set to beat the 1956 record of three days over 40 degrees and may equal the 1908 record of five consecutive days above 40.

If it tops the latter, this month will also become the hottest January in Melbourne in a century.