OK, most of us don't have much of a blast when it comes to running in the summer. As for racing? Yeah, it takes a special breed to be able to peak on a hot and/or humid day. I am not that special breed.
1. Ease Off The Throttle
I have had many races where I knew I was in shape to run, say a 6 minute mile pace but knew the weather distracted otherwise. So I made the decision to run 6:30s instead and finished slower than I wanted but fare better if I had tried those sixes, blew up and ended up walking 15 minute pace. The general rule is that above 55 degrees, for every increase of 10 degrees, marathon pace increases by 1.5-3%. So, in other words, there are going to be plenty of training runs and plenty of races in the hot and sticky months were it just is not going to be optimum for you to go all-out. Accept that and you will have a much better day.
2. You Simply Must Get Fluids
I am know for being a bit of a camel. If the run is going to be less than 90 minutes, even in hot weather, I barely even think of taking a drink of water before I run, let alone taking water with me. But as the weather changes so should your plans. I still rarely take water with me but I know where liquid is available in case I need it. I also know that hydration is something you do before, during and after the run, if you want the best results.
Of course, too much liquid is a problem too. But don't let the fears of hyponatremia (and the rarity with which it happens) keep you from getting your fluids.
3. Mix it Up
Use the summer to work on your speedwork. As I talked about in the Wonderfulness of Track, mixing up workouts is a good thing and in the summer when it is hard to really go long, going short and fast can be greatly beneficial.
4. Know It All Helps
It hurts like the dickens, leaves you crashed on the couch or side of the road and makes you wish for the icy cold hand of winter. Yet working out in this weather, if done right, will make you a better runner. It will make that cool, crisp fall morning where you put on your bib number all the more savory. Remember that much we do as runners is, or should be, delayed gratification. We put in the hard work and effort when others won't so we can achieve the things others cannot. The sacrficies we make in these not-so-prime months will pay dividends in the future.
If you want that first sub-4 hour marathon or the first sub-20 minute 5k, the summer is where those dreams are made.
Go get them.