Acclimate To The Heat
There are two ways to acclimate your body to the heat in the weeks prior to a race. The first way to do it is passively. If you have the ability to go into a sauna or in a warm room to heat your body up prior to training runs, this will help your body get used to running with a warmer core temperature. The other way is to do it actively by adding layers of clothing during easy and long runs, as well as pace-specific efforts. In the final month of your training, start running in long-sleeve T-shirts and then add a heavier layer, such as a light jacket, in subsequent weeks to allow your body to get used to running fast in warm conditions.