The Watchtower deliberately makes the Trinity appear to be much more complicated than it is and never discusses the doctrine as espoused by the majority of Xtian religions, using diversion tactics to insinuate that Modalism represents the Trinity because a lot of prospective converts will fall for the subterfuge and it is an easier doctrine to confuse you with.
Have you seen the official doctrine of the Trinity from the Catholic Encyclopaedia? Do you understand it?
http://www.newadvent.org/cathen/15047a.htm
I'm not suggesting that you should believe the doctrine, just that in order to debate it with a JW, you do have to understand it so that you don't get diverted and confused and steam rolled into debating another subject chosen by the JW.