Ahead of today's opening practice session, the air temperature is 16 degrees C, whilst the track temperature is 21 degrees. It is cool and overcast. We're going to get rain today, but it remains to be seen when and how heavy.

Tyre compound available this weekend are soft and supersoft - as in Monaco - whilst there are two DRS zones, the first on the straight leading to the final chicane and the second on the pit straight leading to T1. They share a single detection point located just before T9.

There have been a number of changes to the track since last year; the wall and fence behind the run-off area at T10 have been renewed, whilst new walls and fences have
replaced guardrails on both sides of the track between Turns 10 and 12. Also, from now on cars straying into the run-off area at T13 will have a new line between bollards to follow when rejoining the track.

The main point of interest here - other than how Hamilton and Mercedes recover from Monaco - is the engine upgrades from Ferrari and Honda, the Italian team looking to bridge to obvious gap to its German rivals.

Brakes are put under enormous pressure here, which could lead to problems for Mercedes, in particular, The German team having shown this to be one of its few weak points.

The lights go green and Massa and Raikkonen lead the way, both, no doubt, eyeing the ever darkening shies. In no time at all there are thirteen drivers on duty.

"I can't get out of second gear," complains Button. And that's on his installation lap. The McLaren driver slowly makes his way back to the pits.

Rosberg posts the first time of the weekend, the German stopping the clock at 1:23.011. Moment later teammate Hamilton posts 20.287 before locking-up in T1.

Ericsson goes third (25.083), the Swede working hard to generate some heat into his tyres. The Sauber driver subsequently improves with a 21.038 as Bottas goes third and Steven fourth, ahead of teammate Merhi.

Another lock-up in T1 for Hamilton, the Briton doing well to catch the car as it slid across the track.

Seventeen minutes into the session, all twenty drivers are on track.

Hamilton posts 17.734 and Rosberg 19.389 as Mercedes ups the pace. The German subsequently improves with a 17.756.

The TV camera pick up on marshals who are removing staples that have been stuck on the track in the pitlane.

As Hamilton improves with a 17.530, teammate Rosberg goes quickest (17.105). elsewhere, Vettel makes hard work of passing Merhi.

Raikkonen is currently third, ahead of Bottas, Maldonado, Hulkenberg, Massa and Grosjean.

Hamilton raises the bar ever higher as he crosses the line at 16.608. moments later, Vettel goes third (17.905).

Bottas and Kvyat are the first drivers to fall foul of the re-profiled final chicane and its bollards.

Told Hamilton's time, Kvyat - currently 13th and 3.170s off the pace - replies: "I don't need to know that, I don't need to know that".

Talking of Hamilton, the Briton hits the kerb as he runs wide in T8/9, sending a tremendous shockwave through his rear wheel.

The opening half-hour comes to an end as Hamilton leads the way, followed by Rosberg, Vettel, Grosjean, Massa, Hulkenberg, Raikkonen, Maldonado, Bottas and Perez. Button is the only driver not to have posted a time.

Bottas advises that the track was improving and that his tyres felt good.

While most pore over the data from their initial runs, Button heads down the pitlane for another single lap.

Ricciardo is out of his car as his crew work on the front of his car, amongst other things the brake ducts are being changed.

As the sun shines, Bottas is told that the start of FP2 should be dry, therefore the team will not make the switch to options until FP2.

After more than ten minutes of inactivity, Stevens gets the session back underway, followed by Maldonado.

Button is back on track and begins his first flying lap of the day. The Briton posts 24.871 having spent much of the main straight weaving from side to side in an attempt to generate heat into his rear tyres. Sure enough, next time around he improves to seventeenth with a 20.199. "It's really pointy, really pointy," he complains.