You shouldn`t wear that shirt if it`s still damp. (=slightly wet, often in an unpleasant way)
I don`t mind how hot it is, as long as it isn`t humid. (=referring to the moisture in the air)
One good thing about the Scottish climate is that it keeps your skin moist. (=slightly wet in a good way)
I was caught in the rain and my clothes are completely wet. (=not dry)