This is how you calculate the heat index, which I discussed at length earlier. If you’re more of a visual person, you can use NOAA’s table. It’s supposed to give you an idea of how hot it feels, or to put numbers to the old adage that “it’s not the heat, it’s the humidity.”
It strikes me as a relatively noncontroversial idea, but there are people who disagree, like Rush Limbaugh (via).
Maybe he’d prefer wet-bulb temperature? I dunno. You’d think someone who lives in Palm Beach would be fine with a measure that combines heat and humidity, but I guess not. Or maybe there’s more to that whole thing about people living in the South being less susceptible to high temperatures than I thought.