An example of ambient humidity and its effect on wood and moisture content: I live in Hawaii, and most days the relative humidity is about 45-50% much of the day. A little higher in the cooler morning. Koa is a tropical hardwood, similiar to walnut in density and hardness. Koa will settle out to about 12% equilibrium moisture content. So if it takes a year or two to dry from green to fully air dry, the equilibrium moisture content will no longer change after that (stays at 12%), unless the wood is moved to a different environment.
Steve