I've noticed that as well on occasion, though it doesn't always seem to happen. It's weird though that sometimes the weather changes from day to day and other ttimes it's painfully slow. A while ago I got stuck in fog with zero visibility for something like two weeks. I had to torpedo ships only with the help of radar and hydrophone. Luckily it was just off the Japanese coast so I figured the risk of friendly fire was pretty low
Torpedo attacks in calm weather and good visibility get's much easier though later on when you get access to the electrical mk.18 torps that are completely wakeless.