I have had a lot of my runners complain about not being able to maintain their training paces in the warmer summer months. The Tinman Heat Index chart is informative and a great reminder about how much your pace is affected by the heat and humidity!
Try to fit in your runs in the early morning or late evening to beat the heat. Stay hydrated both before and after your workout and listen to your body! Back off the pace and refer to Timan’s chart. When that first cool day of autumn rolls in you will feel like a beast out there!