Ahead of today's opening session the air temperature is 25 degrees C, while the track temperature is 37 degrees.

More than most other GP weekends, this opening practice session is pretty unrepresentative and meaningless, what with it taking much earlier in the day than both qualifying and the race. Nonetheless, with new bits to try and four drivers making the Melbourne debut, there is some work to do.

On the other hand, with rain showers and even thunderstorms forecast for Saturday and Sunday, the teams may want to get in some dry testing for Bahrain and China before conditions deteriorate tomorrow.

The lights go green and Vettel leads the way followed by Grosjean, Ericsson and Alonso. Raikkonen is among the early risers, though the Finn has difficulty navigating the narrow pitlane.

Ominously, the last to head out is the Mercedes duo, the German team one of the only outfits not having brought any significant updates here.

Hamilton is straight on to the ultrasofts, while his rivals are on a mixture of softs and supers.

Hulkenberg is the first driver to head out for a second run, the German sporting softs on his Renault. He subsequently pits having failed to post a time.

The track falls silent... something we may need to get used to this year considering the new limit (three) on power units for the season.

After several minutes of silence Russian rookie Sirotkin heads out, the youngster and his team having a lot to prove following a tough pre-season. He is subsequently joined by Ricciardo.

Sirotkin posts the first time of the weekend, year even, crossing the line at 1:32.057.

Moments later Stroll posts 29.403 as Sirotkin improves to 29.342 however, both a demoted when Ricciardo bangs in a 27.608.

The TV cameras cut to the McLaren garage where the new 'Halo friendly' monitor completely obliterates any view of Alonso sitting in his car. Dumb.

Vettel posts 30.108 and Raikkonen 26.989 as the Ferrari duo bookend the five names currently on the timesheet.

Sainz goes seventh (of seven) as Bottas serves notice of intent with a 26.499, the Finn 0.490s up on his countryman. Vettel improves to fourth with a 27.657 as Ricciardo improves to 26.299.

A 26.007 sees Verstappen go top as Hamilton finally heads out again. His first lap is conservative, to piut it mildly, the world champion posting 36.522.

All times posted thus far are on ultras while the Ferraris are on softs and Sainz on supers.

Next time around Hamilton improves to 25.694 only to be leapfrogged by Ricciardo and then Verstappen (24.959) moments later. That fast lap by Hamilton included a huge slide in the penultimate corner.

Thirty minutes into the session all but Magnussen and the McLaren pair have posted times.

Verstappen consolidates his top spot with a 34.936, the youngster going quickest in S3. However, Hamilton is on a hot lap and having gone quickest in S1 and posted a PB in S3 finally crosses the line at 24.914.

The Ferrari pair remain 0.9s off the pace but are on tyres two steps harder than the ultras being used by the Mercedes and Red Bull runners.

As Vandoorne heads out, the Saubers pair assume the same positions the Swiss team habituated for much of last year.

As Hamilton improves to 24.531, Vandoorne heads back to the pits having failed to post a time.

An overenthusiastic Sirotkin is lucky not to clout the wall as he enters the pitlane carrying just a little too much speed.

Forty minutes in and the track falls silent again as the drivers hand back their extra set of tyres.

Back in the McLaren garage and Alonso's car waits as team members appear to be holding some serious discussions at the rear of the car, early reports suggesting that there is an exhaust issue. However, moments later the Spaniard step into the MCL33.

At which point, with neither McLaren having posted a time, it's worth noting that the Toro Rosso pair are 15th and 16th.

After 50 minutes, it's: Hamilton, Verstappen, Ricciardo, Raikkonen, Vettel, Bottas, Ocon, Sainz, Perez and Stroll.

Bottas gets things going again, the Finn subsequently joined by Ericsson and Leclerc.

A 24.577 sees Bottas improve to second just 0.046s off his teammate's pace.

This is normally when attention shifts to Sunday afternoon and the teams switch to long runs however, this could well be influenced by the weather forecasts for the coming days.

As in testing, the Sauber looks to be a real handful, with Ericsson and Leclerc both struggling.

Going quickest in the first and final sectors, Hamilton improves slightly to 24.147.

Vandoorne is the first of the McLaren pair to post a time, but at 29.558 the Belgian will be looking for a serious improvement. Teammate Alonso is still to head out again.

While the Mercedes duo persist with ultras, Ferrari remain on softs and Red Bull switch to supers. Seventh placed Sainz is also on supers as is his Renault teammate Hulkenberg.

Magnussen is back on track, the Dane having completed on 7 laps thus far having suffered a sensor issue. No such problems for teammate Grosjean however, the Frenchman improving to 8th with a 26.458.

Though Raikkonen continues with the softs, Vettel has switched to the supers but a mistake in the final sector, not to mention traffic earlier in the lap, means he fails to improve.

Three PBs sees Grosjean improve to seventh (25.730) as Hamilton consolidates his top spot with a 24.06 having gone quickest in S2. Vettel still struggling to improve on the supers.

Alonso's first lap of the day sees the Spaniard (on supers) cross the line in 14th (26.638), ahead of Perez, Magnussen, Hartley and the Saubers.

A little cross-country for Magnussen who heads off on to the grass in the penultimate corner.

PBs in all three sectors finally see Vettel improve to fifth, 0.969s off Hamilton's best.

While his teammate remains rooted to the foot of the timesheets, Alonso improves to ninth with a 26.285.

Next time around Alonso leapfrogs countryman Sainz for 8th, stopping the clock at 25.896.

"The midfield battle looks just as tight as we expected it to be," admits Pirelli, "only a few tenths of a second to choose between them. But there's no point in trying to draw too many conclusions."

With seven minutes remaining the experimenting continues, the Force India of Perez smothered in flo-vis.

Vandoorne improves to 12th with a 26.541, things appear to be improving for McLaren after a difficult start to the session. However, this means that the Sauber pair, along with Hartley, drop to the bottom.

Ominously, the McLaren pair have both completed among the most laps, though Ocon leads the way. Verstappen, Perez and the Saubers also having been kept busy.

Magnussen, Alonso, Vandoorne and Hartley have done the least.

At the end of the session the drivers head to the grid for practice starts following the decision to lower the starting lights to accommodate the Halo.

The session ends with Hamilton quickest, ahead of Bottas, Verstappen, Raikkonen, Vettel, Ricciardo, Grosjean, Alonso, Sainz and Vandoorne.

Gasly is eleventh, ahead of Sirotkin, Hulkenberg, Ocon, Stroll, Perez, Magnussen, Hartley, Ericsson and Leclerc.

Check out our Friday gallery from Melbourne, here.