I'd say that any fluctuation like that in weight, over such a small time frame, virtually
has to be water. If you think about it what other body mechanism could physically produce the gain?
My tuppence ha'penny on the above discussion would be to aim for the first show regardless of how ideal the categories are just to take the mental leap of becoming a competitor. The second point would be to talk to your mentor about concentrating less on bulking and more on improving the condition. A shape-up style effort between now and Xmas?
Of course the above advice comes with the following caveats; you'd have to accept that you could arrive at your show wanting more mass and the part about working on condition now -well, your mentor might really be that
100% confident he can bring you in on time starting in the spring.
If I am going to get brutally honest I
actually think you should just make improving your conditoning your 100% focus, regardless of shows, mass, whatever. I think you just want to get lean and sooner rather than later.
I may be wrong and I don't mean to speak out of turn