Paris August.

Yes it can be very hot, in the mid to high 20s which is not so comfortable in a city environment. One thing to consider if going to Paris at this time is the fact that many museums etc close for a couple of weeks in August, it's a big annual holiday time there so if that's what you're visiting for you might be disappointed. Better to check in advance before you're booking.
 
August is supposed to be a great month to go to Paris as the average Parisian gets out of there so there are fewer people. However the reason the average Parisian gets out of there too is because it's hot...so what you gain on one side you lose with the other. I was in Paris two years ago end of July and whilst it was hot, it wasn't unbearable, although two showers were required and plenty of sunscreen. We were in a small hotel in St Michel, you can request a/c units in most places if you don't get one by default. There are water blowers at d'Eiffel Tower and it's not as if you'll be out in the sun basking all day...nothing that a couple of beers and icecreams wouldn't help with. Catacombs (underground and cool), museums, you can avoid a lot of it ...Highly recommend tour bus - get ticket for two days, not much in price between one and two days...bon voyage
 
Yes, Paris is a bit muggy in August. Lots of Parisians chase their psychoanalysts to the south coast and further afield. But the upshot is that you get more pavement for your buck. Some restaurants also close - especially Italian. A votre sante!