Today's prompts take advantage of that mood. Choose one, find a piece of shade and write the afternoon away.
The day is hot, hot, hot and your protagonist is a child at the beach. Who is he/she with? Why are they there? How does he/she feel about the heat? Is your character tired and cranky or does he/she want to stay in the sun longer than is wise? Write in first person from the child's perspective.
A beautiful glen stretches before you on this warm summer day. Describe it so that anyone reading your piece can see what you see and feel what you feel.
The sun is shining and it's a beautiful day outside. Just a hint of breeze blows the leaves. Your protagonist is working inside an air conditioned building with no windows. Write a conversation he/she has with his boss.
Have fun -- and enjoy the weather!