It will move some but as Bud said, follow the manufactures recommendation for acclimation. It will swell a bit with higher humidity and shrink a little when its less humid. The 'swelling' wont likely even be measurable and certainly not noticeable. Where it sometimes goes awry is when it acclimated in a very humid environment and then shrinks (when AC is on) and you have slight gaps between boards. If you are concerned, acclimate it with the AC on. Or better yet, acclimate it in the environment you are most likely to encounter. In other words, if you never run the AC then acclimate it that way.