what is the climate like in france during august/september/october.
I have been to Paris in Mid-late October and early November 3 times, and it was wonderful weather. Hardly any rain. Mild temperatures. But I always monitor an internet weather site for the countries I'm going to before I leave, and pack accordingly. From my experience (also going in April and January) you probably do not need any rain gear other than an umbrella -- unless the forecast is showing a big storm system.
Here's a great place to find out on weather history from past years by week or days, etc. I use it planning my trips all the time... http://www.wunderground.com