I'm confused by the skepticism displayed here. Drag on a ball can be easily predicted as:
D = 1/2(rho)(C_d)(A)(V)^2.
rho = air density
C_d = drag coefficient (constant value for a baseball at a constant exit velocity)
A = projected area (constant for a baseball)
V = velocity of baseball
It is well known that air density decreases with increasing temperature and humidity.
So, for the same exit velocity off the bat, if the temperature is higher, air density decreases, drag decreases, and the ball travels farther.