The Killer Heat
The Body's Response
The end result is that you are unable to reach your normal exerted workloads, you breath heavier, you sweat more, and your muscles are exhausted much quicker. But, we are adaptable beings and we can overcome these adverse effects.
Unfortunately, the benefits of acclimation can easily be lost after only about a week of being out of the sun, but stick through the heat and your body will acclimate accordingly. The best thing you can do in preparation is stay hydrated and drink plenty of water throughout your workout.