Ahead of today's opening practice session the air temperature is 17 degrees C, while the track temperature is also 17 degrees. After several days of sunshine, as widely predicted, it has been raining for a couple of hours, though Saturday and Sunday are expected to be dry.

Red Bull can secure its second successive constructors' title this weekend however, celebrating its 700th Grand Prix, McLaren would dearly love to upstage the Austrian team.

Jean-Eric Vergne replaces Jaime Alguersuari in this session, the Frenchman having just secured the runner-up spot in World Series by Renault Championship. Karun Chandhok is in Jarno Trulli's Lotus while Narain Karthikeyan is in Tonio Liuzzi's HRT.

Tyre compounds this weekend are soft and supersoft though it is unlikely we'll be seeing much of them this morning.

The lights go green and surprisingly there are a few eager beavers including Ricciardo, Karthikeyan and Vergne. The Indian driver preparing for his return to the race seat for his home race in two weeks time.

One by one more drivers pour on to the track, almost literally, including Rosberg, Massa, Webber and Schumacher.

Ten minutes into the session the McLaren duo are the last two drivers to make an appearance. Even on the extreme wets it is remarkably slippery.

As drivers talk, joke, drink (energy mixes) and grin at the cameras, the fans in the stands wait expectedly. Half-an-hour into the session Hamilton is the first driver out for a second run. After a single exploratory lap he returns to the comfort of his garage.

Fifty minutes into the session Hamilton comes out yet again, however, it remains very, very wet, visibility is poor.

As the McLaren driver stays out for a rather wet flying lap, he is joined by Buemi and Chandhok. The Englishman crosses the line at 2:05.484, watched by Fernando Alonso who looks far more comfortable back in the Ferrari garage.

With lots of standing water, and having been told to take it easy, Chandhok pits after just one lap. Hamilton, meanwhile, improves to 2:03.391. Buemi goes second with a 2:07.906.

Hamilton returns to the pits as Buemi improves to 2:04.554 and Ricciardo posts 2:13.882 to go third. Vergne, Kobayashi and Rosberg are now on track.

Buemi goes quickest with a 2:03.182 as Maldonado runs wide as he leaves the pits. Kobayashi goes third (2:06.423) ahead of Ricciardo and Vergne.

Rosberg posts 2:06.241 to go fourth as more drivers head down the pitlane. More drivers means more traffic and consequently next time around Rosberg fails to improve.

With 20:00 on the clock, there are just nine names on the timesheet: Buemi, Hamilton, Schumacher, Kobayashi, Rosberg, Vergne, Maldonado, Ricciardo, Karthikeyan and d'Ambrosio.

Schumacher runs wide and di Resta spins, as does Perez, as conditions appear to worsen. McLaren reveal that they are finished for the session.

Although it is still raining, Sutil, currently fourth on 2:03.800, goes quickest in S1. He loses a little pace in S2 finally crossing the line at 2:03.756. Elsewhere, Vergne locks up at the rear and takes full advantage of one of the large tarmac run offs.

Di Resta improves to fifth with a 2:03.950 watched by (2012 teammate) Nico Hulkenberg.

While Webber shows no sign of making an appearance, Vettel heads down the pitlane, the German usually revelling in such conditions. That said, the world champion runs wide at Turn 10, as does Chandhok moments later.

Having posted a 2:15.437 on his first lap, Vettel sets about improving on the second. A 2:04.425 sees the Red Bull driver go seventh.

As Barrichello complains about the handling of his car, unsure whether its aquaplaning or simply stalling, former Ferrari teammate Schumacher goes quickest in S1. The German has a poor middle sector as Karthikeyan has a big, big spin.

Sutil goes quickest with a 2:03.141 as fellow German Schumacher once again goes quickest in S1. Elsewhere, Vettel does brilliantly not to collect one of the Virgins. Schumacher goes quickest with a 2:02.784 ahead of the world champion who posts 2:02.852.