Rio is HOT all-year long. Sometimes hot, sometimes scorching!
For a CARIOCA a citizen who lives in Rio 19C (60F) - during the night- is Cold. If your final city is Rio travel with light clothes and one coat (not a heavy one).
I'd say for a tourist it's better to come to Rio during (our) winter as you can stroll easier and enjoy the city.
Ah.! In July it hardly rains !