I'm running my first half marathon at the end of June after a training plan of 17 weeks and I have another half planned for the end of September (23th) as well.
For the summer heat, the best is to train early in the morning or at night... it is way less struggeling (to me, at least)
Is there a reason you want to wait 6 weeks before you start training? Because depending when in the fall you want to run one, you might want to start early (my program for beginners was 17 weeks long...)