Ahead of today's opening session, the air temperature is 24.7 degrees C, while the track temperature is 40.4 degrees. The skies are blue and it warm... and getting warmer.
At Williams, Nicholas Latifi takes over George Russell's car, while at Ferrari attention will no doubt be on the stewards hearing that follows the session as the Italian team attempts to overturn the penalty handed to Sebastian Vettel in Canada.
Ferrari is one of several teams running updates this weekend, and while Vettel and teammate Charles Leclerc will have a new front wing, Max Verstappen, Pierre Gasly and Daniil Kvyat will all have the latest-spec Honda engine.
There's an upgraded engine for Daniel Ricciardo also, while teammate Nico Hulkenberg misses out as he would have incurred a grid penalty.
The lights go green, and local hero Grosjean is among the first out, followed by Giovinazzi, Norris, Sainz, Kvyat and Magnussen. Vettel is among the early risers.
Sainz wastes no time in putting a score on the board, the Spaniard stopping the clock at 1:35.909.
Leclerc posts 36.934 and Vettel 38.853, before the Monegasque improves to 35.822.
There is something very weird, my tyre is dead," declares Leclerc as a worrying 'stripe' appears on his right-front.
Apparently, Leclerc is running the old front wing, and Vettel the new version. That said, the German reverts to the old version for back-to-back analysis.
There follows a spell of inactivity before, around 18 minutes in, drivers start heading out again.
A spin for Kvyat in T5 sees an early appearance of the yellow flags. Replay suggests a snap oversteer. Incidentally, the Russian will start from the back of the grid on Sunday after taking all manner of new components.
Sainz retakes the top spot with a 35.752, ahead of Leclerc, Vettel, Gasly, Norris, Kvyat and Albon.
"You can't do two consecutive laps with the tyres," reports Vettel.
As Latifi reports "cutting in seventh gear", Hulkenberg reports that his cockpit is like a "barbecue". Indeed, moments later worrying smoke can be seen appearing from beneath his steering wheel.
As he exits the pits, Vettel has to take avoiding action in order to avoid Bottas who was on a flying lap. The pitlane exit, of course, has been re-profiled in order to avoid just such incidents.
"That was a mess," says the German, "I chose to go right just to avoid people."
"I don't know what's going on," complains Verstappen, "I'm sliding more and more, there's no grip."
A 34.695 sees Bottas go quickest, ahead of Gasly, Norris, Verstappen and Sainz.
As Bottas, who has improved to 34.500, reports his steering as being "spongey", Verstappen, despite his issues, goes second, just 0.095s off the pace.
At 40 minutes, it's: Bottas, Verstappen, Hamilton, Norris, Gasly, Sainz, Ricciardo, Perez, Leclerc and Vettel.
Haas reports a suspected water leak on Grosjean's car.
At Renault the plank on Hulkenberg's car has been cited as the source of that smoke and as a consequence has been changed.
Following another lull, Norris heads out to get proceedings underway again. His car sporting lots of lovely flo-vis. The McLaren driver is currently 4th, 0.499s off the pace.
Bottas's best was set on the softs, while Verstappen's was on the mediums. Gasly, Sainz and Perez were also on the yellow-banded rubber which suggests it could be the way to go.
A 34.271 sees Gasly go top, with Norris crossing the line at 34.110 shortly after.
As in Canada, the Alfas are worryingly off the pace, Giovinazzi and Raikkonen currently both over 2.7s off the pace.
Ricciardo improves to fifth with a 34.712, but is demoted when Hamilton posts 34.106 to go top.
Gasly subsequently posts 34.091 and Bottas 33.779.
As the qualifying sims continue, Verstappen switches to the softs. Having dropped to sixth, 0.816s off the pace, he improves to second with a 33.618, just moments after Hamilton had raised the bar with a 33.272.
With 22 minutes remaining, the Ferrari pair are down in 15th and 16th, both over 2.5s off the pace, having completed 10 (Leclerc) and 13 laps (Vettel) respectively.
As Bottas posts 33.173, Verstappen spins at T8 bringing out the yellows after losing the rear as he carried too much speed into the chicane that divides the Mistral Straight.
The Racing Point pair remain the only drivers still to try the softs.
As Gasly complains about the traffic, he is basically told; "well I can't do anything about it".
As Hamilton retakes the top spot (32.738), Leclerc goes third (33.111) as teammate Vettel heads out.
"There is something loose by my left foot," reports Kvyat.
A PB for Vettel is S1, but he is already 0.28s off the pace. At the second split he is 0.779s down, finally crossing the line at 34.904 to go 12th.
"Something doesn't feel right at the front," warns Vettel. Elsewhere, Hamilton has gone wide following a lock-up.
Told he can do another lap, Norris responds: "There's no pint, I can't tell you anything. The tyres are too destroyed to give you any feedback." So that's a no then.
On his second hot lap, Vettel posts PBs in all three sectors, and while he improves to fifth he remains over a second off the pace.
A spin across the kerbs for Gasly at T3. "Not good," says the Frenchman.
The session ends. Hamilton is quickest, ahead of Bottas, Leclerc, Verstappen, Vettel, Gasly, Norris, Sainz, Ricciardo and Albon. While Perez is eleventh, ahead of Hulkenberg, Stroll, Kvyat, Magnussen, Raikkonen, Giovinazzi, Latifi, Kubica and Grosjean, who completed only 9 laps due to that water leak.
The sessions for the support races should help improve the track over the next couple of hours, and hence ease the graining witnessed over the last ninety minutes.
However, warmer temperatures, and the wind - it's not called the Mistral Straight for nothing - will bring their own problems.
Check out our Friday gallery from Le Castellet, here.