The effect of heat is much greater than that of humidity -- the ball does go a tiny bit further in humid air, but it is only maybe a yard's difference between a 'very dry' and 'very humid' day in any particular locale.
http://wahiduddin.net/calc/calc_da.htmHere's a neat little web site you can plug the numbers in to compare "relative density". Consider 100% to be normalized sea level density -- plug in 16 feet altitude, 57 degrees, 30" barometric pressure and 57 degree dewpoint and you get 100% relative density or normalized sea level. Those are conditions on a cool clammy day at Pebble Beach, for example.
If you plug in 1/2 mile elevation (2640 feet) 95 degrees, the same 30" pressure and 60 degree dewpoint, for Sand Hills on a typical summer day, you get 84.54%, meaning the air is about 15% less dense there. That doesn't mean you'll carry the ball 15% further, since drag isn't linear to air density, but it helps you see the magnitude of the difference between various conditions.
High ball hitters get more help/hurt from air density since drag is a bigger factor the longer the ball is in the air. The less dense the air is, the less effect wind has on the ball, and the harder it is to get the ball up in the air via backspin (so you might want a higher lofted driver in Denver than in Palm Springs) However, the ball will lose less spin during its flight so it will bite a bit better in less dense air.
Altitude and temperature dominate, and air pressure makes more difference than you'd think, but even Tiger isn't precise enough to tell any difference humidity can possibly make.