If you're planning to get home by cramming yourself onto a Tube train today, prepare for an unpleasant journey.
And, thanks to the brave souls at Gizmodo, we now know exactly how unpleasant it will be, after it lodged a freedom of information (FoI) request to find out which are the hottest Tube lines.
Surprisingly to City workers forced to endure the Central and Northern Lines every day, the Bakerloo Line takes the crown, with an average August temperature of 31.04 degrees centigrade.
That's followed by the Central Line, with an August temperature of 30.47 degrees, while the Victoria Line follows, at 28.03 degrees. The Northern Line is a comparatively balmy 27.98 degrees.
Meanwhile, lines on the surface - the Circle, Hammersmith & City, District and Metropolitan Lines - peak at just 25 degrees, and fall as low as 13.4 degrees in February.
This weekend's heatwave is due to carry on well into this week, with the mercury in London expected to hover around 30 degrees until Thursday.
The high temperatures caused the Met Office to issue an amber alert warning of a heatwave, with Public Health England advising people to drink plenty of water, keep out of the sun at midday, and wear light clothes.
Meanwhile, trade unions implored employers to ditch their dresscodes so workers aren't forced to toil away in suits.
“Obviously shorts and flip flops won’t be the right attire for all workers, but no one should be made to suffer unnecessarily in the heat for the sake of appearances," said Frances O'Grady, the TUC's secretary general.