For further reading regarding the failures of German torpedoes, I would suggest this little gem:
http://digitalcommons.georgiasouther...99&context=etd
I haven't gotten through all of it yet, but thus far it has proven to be a well researched and well written thesis on the German torpedo crisis that occurred early in the war.
Given what I have read thus far regarding the depth keeping springs, heavy waves would definitely have an adverse effect on torpedo reliability. The depth keeping springs were not thoroughly tested, or reliable, to begin with; combined with the constantly changing water pressures that come with 2-3m swells, I can easily imagine some failures being the direct result of heavy waves. To bring wind speed into the equation, winds above 15kt can easily cause swells of 3m or higher.