If you want to save your wallet the hassle down the road, don't buy seasonal clothing (shorts, etc.) in the size you believe you will be at a particular time, or you will be disappointed/elated. You are obviously not a good judge of how big or small you are and will not make the right choice.
Why the warning? Well today I pulled out a nice pair of dockers 38 shorts to wear today that I had bought at the end of last year's shorts season, and realized that I am already in 36s. In fact wearing minimal 38s anymore. I put them on to see since everything is different, and these didn't fit. The price tag is still on them though so they will be sold and someone larger than me will be able to use them. This is a good thing!