Murdoch earned a fifth and a third in yesterday's two races in blustery conditions, lifting him up the standings from fifth.
Sweden's Max Salminen is five points adrift in fourth.
Today's programme includes a medal race for the top 10, worth double points, while those outside the top 10 are scheduled to sail one final fleet race.
"It was good to get two races in the bag that were definite keepers," says Murdoch.
Following two poor races on Wednesday, dropping him to 14th, Murdoch has been in catch-up mode.
"It's a shame that day three didn't go the way I wanted but I'm pretty proud of myself to come back out swinging from that and have a couple of good days," he says.
"That was the main goal after day three - to get myself back in contention for a medal again and I've managed to do that, and I'll be fighting hard for it [today]."
The weather forecast is not good, with an ominous light, variable prediction looking favourable for weekend beach-goers but not for the Olympic Finn fleet.
Murdoch isn't concerned about racing in light airs.
"On day three, some of the choices I made on the first beat set me back. I came off the start really well in both those races. I don't think I've got any issues in the light airs - boat-on-boat, I was more than fast enough.
"I think that I've shown myself that regardless of the conditions [today], I'll be well in the hunt for a medal."
Junior was 21st and 22nd on the water yesterday and a good race today could see him improve, with just three points to 13th.
If wind permits, racing starts at 11am today.
