Ahead of today's first free practice session the air temperature is 19 degrees C, while the track temperature is 20 degrees.

Following days of predictions about the weather it is wet and overcast. There was rain throughout the night and again earlier this morning, and while it stopped for a while around ten minutes before the start of the session it has started again, albeit lightly. The dark skies suggest we are in for more today and for the rest of the weekend.

The tyre compounds this weekend are hard and medium, though in both of today's sessions teams will have access to the latest-spec 2014 prototype tyres... not that we're likely to see much of them this morning.

There are two DRS zones, one on the main pit straight and the other on the back straight between Turns 3 and 4.

As in Austin, Daniil Kvyat is on duty for Toro Rosso, the Russian youngster at the wheel of Daniel Ricciardo's car, while James Calado replaces Paul di Resta and Rodolfo replaces Max Chilton.

Kvyat is talked through the various dials and buttons on his steering wheel. Rather him than us.

The lights go green but as one might expect there is no rush to get to work. That said, three minutes into the session Bianchi leaves his garage. The Frenchman completes one lap of the soggy circuit before diving back into the relative comfort of his garage.

Gutierrez, Bottas, Gonzalez, Rosberg, Hulkenberg and Maldonado test the conditions.

Ten minutes into the session all but Perez and Calado have been out.

Despite having won both titles several races ago, both Red Bulls are sporting an array of sensors and lashings of flo-vis. Of course, the Austrian outfit is really already looking ahead to 2014.

In his final race for Ferrari, Massa is sporting a tribute helmet and overalls.

Button posts the first time of the day (26.184) but this is soon beaten by Rosberg who crosses the line at 25.747. Both drivers are on Inters while some prefer the full wets.

As Rosberg runs very wide at T1, Button raises the bar with a 25.391 before the German responds with a 24.781.

A big slide and spin for Hamilton coming out of T3. Stranded in the middle of the track, the Mercedes driver is eventually able to reverse and get going again.

"Car is very on the nose, car is very on the nose," says Button who subsequently pits to decrease his front wing flap angle.

Twenty-five minutes into the session there are fourteen names on the sheets, Rosberg heading Button, Hamilton, Perez, Hulkenberg, Kvyat, Sutil, Gutierrez, Bottas and Vergne. Everyone now on Inters

"Really struggling to get heat into the tyres," says Button, "we need to find out if it was taking front wing out of it or if circuit's getting wetter."

Hamilton makes it a Mercedes 1-2 with a 25.230, though the Red Bulls, Grosjean and Calado have yet to post times.

Gutierrez is informed that Hulkenberg is gaining time in Turns 6 and 7 by carrying 4th gear through the corners. While Hamilton is informed he's losing time to Rosberg in Turns 6, 7 and 11.

Forty-three minutes into the session Vettel finally heads down the pitlane, the German sporting a set of primes. This comes as Grosjean, Maldonado and Gonzalez are shown slipping and sliding on the Inters.

As Alonso goes fourth (25.593), on-board footage shows just how slippery it remains.

Kvyat improves to sixth (26.064), as in Austin the Russian youngster looking very confident.

Back in the pits, and still to post a time, Vettel heads out on a set of the 2014 development tyres. “It's raining harder now,” he is subsequently told, “we've got the data we need... box”.

Just after half-time, it's: Rosberg, Hamilton, Button, Alonso, Perez, Kvyat, Kovalainen, Hulkenberg, Massa and Gutierrez.

"The track conditions is getting worse, no?" says Perez, who is informed conditions are indeed worse and others are "struggling to run in the 27's.

After a near-miss with Van der Garde, Grosjean tells his team: "Hey, we need to talk to the guy at Caterham, almost hit and run off track". "OK, Romain, we will talk to them," is the response.