Vettel, who completed 65 laps, admitted that rain and strong crosswinds meant gathering meaningful data had been extremely limited.
Despite that the defending champion said Red Bull still had reason to be encouraged given the balance of the RB9.
"It was a rough day with a lot of crosswind and gusts, so it's not easy to read the data even though we collected some," said Vettel.
"It's difficult to compare things you are testing and to compare to other teams and drivers, and it's very difficult to know in terms of pace where we are right now.
"But I would be happy, because generally we are happy with the balance of the car.
"It does what we expect and it seems to behave. If you compare I think it is a better starting point than what we had last year."
Vettel said the tricky conditions also yielded up the possibility of teams springing surprises when F1 travels to Melbourne for the season-opening Australian Grand Prix.
"Conditions are very different to what we will see in Melbourne, so I don't think it will be a surprise if someone all of a sudden deals better with the conditions we face there," he said.
"Overall I think it has got tighter again this year, so it will be close until the end I guess - and we are not even at the beginning."
AUTOSPORT special testing coverage:
Gallery Testing blog Technical blog Live commentary