When, and if, I decide to attack in that kind of weather I plot the ships course as precise as possible and get myself positioned ahead and on the same "line".
Let the ship overtake you, and hope itīs not just a fishing boat
, staying some 50-100m to the side on parallel course.
Set your torpedoes to magnetic pistol and fire them when the ship is closing to 300m ahead of you, almost out of sight.
But if itīs some 15m/s wind and heavy sea I donīt bother, too big risk of waisting
expensive torpedoes.