I live in the tropics where it is hot and humid year round. Personally I would keep the distance but run slower.
Run either very late or very early to avoid the afternoon heat
Stay hydrated, drink a lot throughout the day and not just before running!
Use isotonic drinks or mix some salt into your water to keep electrolytes high when sweating
Don't blame yourself for stagnating or reduced performance! I found that between running in the morning and afternoon here the heat and humidity alone can raise your heart rate by 10bpm!