Be upfront about it without a doubt............
And yes, you should at least try to get going now. Contact the local alumnae chapter and see what their reaction is. All of us can only tell you what WE would do, the important thing is how they react. They may also agree with us.
The alumnae chapter should be having a number of events coming up and you should have plenty of time to meet the members. In my opinion the worse case might be that they invite you to all of their events but tell you that you'll have to wait until you get to your new home to actually initiate.
If it was me <putting back on my AC President's hat> I would not care too much (we have members who move ALL the time) that you were moving PROVIDED I was convinced you were going to stay involved at your new home. Our AC consists of younger women and we have quite a few who move here, get involved for a short amount of time, and then move and get invovled somewhere else. As long as you remain involved, I don't see teh big deal.