Ahead of today's opening session, the air temperature is 24 degrees C, while the track temperature is 27 degrees. Humidity is 90% and it is raining... as it so often doe here at this time of day.

Taking place much earlier in the day than any other session, much like Singapore, this session is pretty much irrelevant.

That said, for Charles Leclerc, Sean Gelael, Antonio Giovinazzi and Sergei Sirotkin it gives them time in an F1 car over a GP weekend, while at Toro Rosso, Pierre Gasly makes his debut.

With an eye on the very heavy rain, the start of the session is delayed "indefinitely".

While there will be further rain throughout the weekend, and lots of it, the drivers are severely limited in terms of the number of wet tyres available, consequently they will want to save them for Saturday and Sunday.

The safety car makes a couple of brave inspection tours but it is clear there won't be any action any time soon.

Nineteen minutes into the session, such as it is, Race Control reveals the session will begin at 11:30 (local time), giving one hour of running. Nonetheless, the wet tyre availability issue still applies.

Sure enough, at 11:30 the lights go green and after a short delay Alonso gets proceedings underway, his McLaren fitted with the halo, thereby allowing some much needed wet running time.

The Ferraris follow the Spaniard, all three of whom are on the full wets. Natch.

As Raikkonen heads back to the comfort of his garage, having warned about the engine mapping, a whole host of other drivers head out to test the waters, so to speak.

Giovinazzi is told to "be careful" as there is very low temperature in the brakes.

Forty minutes into the session, all bar the Bulls, Mercedes and Pink Panthers have been out.

One of the last out is Gasly, who wisely takes his exploratory lap on a 'softly, softly' basis.

Following several more minutes of nothing, as the rain eases off almost entirely, the Panthers head out, both shod with Inters.

Ricciardo is next to venture out, the Australian clearly struggling.

56 minutes into the session, Vettel is the first driver to head out for a second run, while Ricciardo remains on track also.

Verstappen heads out also, as does Raikkonen. Both on Inters.

Ricciardo posts the first time of the weekend, crossing the line at 1:55.601.

Asked if he wants to stay out, Verstappen says no, calling for more wing front and rear.

Vettel posts 54.463 and Raikkonen 54.884 as the Silver Arrows pair finally head out.

A spin for Sirotkin at T2.

Hamilton wastes no time in getting into it, the Briton the fourth driver to post a time (56.089), with teammate Bottas posting 56.666 shortly after.

No sooner has Ricciardo gone quickest (53.103), than teammate Verstappen responds with a 51.201. The Dutchman had previously been told to up his pace as his tyres were cooling.

Gelael goes 18th (of 18) leaving Alonso and Massa as the only drivers still to post a time.

Quickest in the first two sectors, Ricciardo goes quickest with a 51.194.

As Vettel heads off into the grave after locking-up, teammate Raikkonen almost trips up over a slow Leclerc.

Bottas posts 52.654 to split the Ferraris, only to be demoted when Raikkonen goes third with a 52.408.

In the McLaren pit the crew are using fans to try and dry the apron, however it is still raining.

Aware that the conditions, should they persist, offer another golden opportunity this weekend, Ricciardo is the busiest man on track. On his twelfth lap the Australian consolidates his top spot with a 49.719.

However, there is further method to his madness. Following the scare in Singapore, when it was feared a gearbox issue might end his drive to a podium finish, he is running said gearbox this morning to check and see whether he can continue with it or replace it... meaning a grid penalty. So far, so good.

A spin for Wehrlein in T10, "I locked the front," admits the Sauber driver.

Bottas improves to third and Stroll fourth, while Sirotkin is up to seventh.

Despite the conditions, Raikkonen is quickest in the speed-trap, the Finn clocked at 188 mph.

"Three percent shallow, three percent shallow," Hamilton is told. "It wasn't intentional," he responds. Shallow, Moi?

Gasly improves to seventh, eight spots ahead of Gelael.

A 51.518 sees Hamilton go third.

No messing about from that wild old fox Alonso, who, following a couple of exploratory laps, bangs in a 50.597 to go third. The sides of the McLaren smothered in flo-vis.

A late improvement sees Vettel go fourth (51.009), though the German is subsequently demoted by his teammate who posts 50.734.

An even later improvement sees Verstappen leapfrog his teammate also, the 20-year-old taking the top spot with a 48.962.

The session ends, Verstappen is quickest, ahead of Ricciardo, Alonso, Raikkonen, Vettel, Hamilton, Bottas, Stroll, Gasly and Sirotkin.

Palmer is eleventh, ahead of Vandoorne, Ocon, Gelael, Perez, Leclerc, Wehrlein, Grosjean, Giovinazzi and Massa.

Check out our Friday gallery from Sepang, here.