As a once-practicing, but now retired, theoretical thermodynamicist, I was going to pontificate on dew point and relative humidity, as I understand it pretty well. But Stan, whom I will call a practicing thermodynamicist, insofar as he actually makes stuff that deals with this sort of physics vs. just sits there with his computer and contemplates the pertinent partial differential equations, has nailed it down pretty tight. So I defer. We live in a water world, and nothing quite affects just about everything so much as the evaporation and condensation of water in our atmosphere. Your beer is going to get warmer quicker on a 90F, 80% RH day (dew point 83F) than on a 90 degree 40% RH day (dew point 62.4F). The dew point is the temperature of the water molecules as they condense on the outside of that cold beer can.
I was out in Albuquerque New Mexico in May once upon a time, and it was a really beautiful day, Blue-bird sky, gentle breeze upper 70s, may be 80,, hard to tell. Had the radio going, The guy came on and mentioned the current weather by noting the temperature and humidity, which he said was 5%. FIVE!!??? Is that even possible? I think he made a mistake, or I heard wrong. Even at 90F air temp and 5% RH the dew point is 10F. We were not freezing.