Hmmm.... from how you described the sequence, seems that it's a very risky manoever. If it were me, I rather be on silent speed or "silent stop", carefully align the torpedoes and fire when conditions are right. If that's impossible, I rather dive deeper and let him pass, if he hasn't seen me - it will be a bad day if he puts me on the defensive, just like this -->
Movies wise, Das Boot is more or less accurate from how they approach and fire torpedoes. The captain there lost sight of the approacing destroyer, which happens to me in rough waters/bad weather. I also remember the moment they attacked the convoy, doing the calculations and all, whilst they forgot that a destroyer is approaching them... ALARM!!!