You can tell the rut is about to begin when you start seeing rutting activity. Rubs, scrapes and bucks chasing does.

Weather will wffect the rut. If it's hot alot of the rutting will take place after dark when it's cooler. Same with a full moon the bucks will do alot of chasing at night.

I've also read articles that state the moon has something to do with the rutting cycle. After seeing how much the moon effects all animals I wouldn't doubt it.