Sebastian Vettel remains hopeful that Ferrari can make a substantial stride overnight after ending the first day of free practice for the Brazilian Grand Prix almost a second adrift of Mercedes.

Despite more than one off-track moment over the course of the day as most drivers struggled for grip around the Interlagos circuit, Vettel was third fastest behind Nico Rosberg and Lewis Hamilton in both sessions.

However, with almost a second splitting Vettel from FP2 pace setter Rosberg, the Ferrari driver is disappointed to be so far adrift, even if he remains optimistic that he can be closer come qualifying.

"I'll give you my number later and if you see the guy called grip, you'll just pass on my number now," he joked.

"It is a second too much, but we didn't get the best timing for our run," he said. "It was tricky for everyone, a couple of drops of rain, but overall, I think it was a difficult day. We can still improve though. I am looking forward to doing the analysis now and hopefully tomorrow we can do a step forward."

With temperatures and humidity soaring, the conditions have raised the possibility that Ferrari couldn't mount a challenge similar to that of the Malaysian Grand Prix. However, Vettel says inclement forecast threatens to scupper that.

"I think it was supposed to rain today but it hasn't so far. They say the same for tomorrow and then again on Sunday. Here you never know with the weather, you need to look up and see what it is."