If you can find a nice place away from crowds, September can be a nice time for caribou - some times there are frosts that knock down some of the bugs, the cooler weather can make a better time to care for the meat, and with more leaves off the trees, and brush visibility can be better. Also by then the moose hunters may be gone - depending on area and season. The later you go in September, the more careful to avoid big bulls that may be getting rutty and really nasty to eat - but nmis Sept is usually ok.