[XXi]

I did several surface attacks in very poor weather conditions. Still, the best way is to enter the convoy submerged and then surface, when you know you`re in the middle, encircled by merchants, not DD`s. It is always risky as escorts can take you by surprise, you have little time for targetting and choosing targets, finishing the vessels off with a deck gun is not an option... And don`t forget the premature detonations, in storm they`re more a rule thank exception.
THe only good thing in very bad weather is it doesn`t help your enemies either - until they have no radar, they can loose contanct on the surface. And asdic gets interrrupted so that your chances of escaping are rising.

Anyway, for me best weather to attack is moderate to bad. Very bad is just too problematic, clean weather means the risk is much higher.