Not counterintuitive. On the contrary. Water vapor is less dense than atmospheric gases. Hence, humid air is less dense than dry air and the ball will carry better. Air density is a major reason that Fulton County stadium in Atlanta was also known as The Launching Pad. First, Atlanta had the highest elevation of any MLB city at the time. Phoenix (just barely) and Denver have since supplanted it from that status. Second, Atlanta tends to have warm temperatures. Third, Atlanta tends to have higher humidity. Of course, the fact that it was a small stadium also helped a lot. I'm sure #44 was very glad to have played so many games there.