In this case, I'd track a convoy until the weather improves. It's a long way to England, so you can wait.
Early in the war, when the escorts don't have a radar, maybe I'd try a surface attack. I did it once and it was interesting.
I torpedoed a few ships from very close range, until one escort emerged from the fog, steaming at me. She rammed me as I dived, but fortunately didn't hit me with DC. I got away.