I visited Iguazu in January 1990. At the airport, we saw a temperature display of 46C - and indeed, we had to land in Argentina because the Brazil airport runway was melting.

This is absolutely the hottest place I've ever been. And the rickety motel we stayed at had poor A/C that both kept us awake, and didn't actually cool the room very much.

Keep this in mind for planning a trip - and it really is worth the trip!