I walked the Le Puy route as far as Auvillar the full month of June and the weather was mostly ideal; not too cold, nor too hot. I only recall a couple of afternoon light showers, and one short rainy afternoon.
Although I normally walk in the spring, I chose June because my teacher friend was not available . Also, on this forum it was mentioned a few times that there were no French holidays in June, which avoids some of the French walking groups of friends.
I walked from Le Puy to Conques Oct 1-10 four years ago and had ideal weather. Then I picked up where I left off, Conques to Miradoux mid-Sept 2021 and had quite a bit of rain and a lot of mud so I guess it’s not easy to predict.
I walked from Le Puy to St. Jean this fall, Sept 5 to Oct 11 and had great weather - sunshine, blue skies, low to mid 20s C., only 2 days of mid 30s. There was one afternoon of rain and wind, and a few odd showers and foggy mornings but that was it. It warms up as you leave the higher Aubrac plateau and are down in the lower farming areas. Towards the end of Sept, the mornings were cooler, 7-8 degrees but with the sun it warmed up quickly. It was a hot dry summer-fall in Europe, and that seems to be the way the weather is going, but who really knows!
Sept can be a busy time for French walkers, but this camino is much quieter than the Camino Frances, and I didn't find it that crowded once everyone spread out over the route. My advice is to learn some basic French, if you don't speak it already. It is definitely an immersion experience. Bon chemin! You'll love it!
I walked Le Puy to Roncesvalles from Sept 28 to Nov 2, 2014, and encountered a heat wave midway (30-35C for more than a week) and a day or two of showers, but otherwise it was quite nice. To me, a bigger issue than weather was noise. It was autumn, the harvest was in full swing, and there was a constant din of machinery and, often, tractors bearing down on me on the road. I would probably not walk again in that season in southern France, even though the countryside is beautiful. And I do realize that I'm sensitive to noise and that not everyone would be bothered by this!
We walked from Le Puy to St. Jean from late August to early October (2018). Going through my photos reminded me of how much we loved this walk. The scenery is beautiful and the food is delicious. We used our phone translator A LOT, but that worked just fine.
It was very pretty in autumn. The weather was perfect with just a couple of rainy days and a few very hot days. I found myself wondering what the fallowed fields looked like in spring; I think we will have to go back and find out (so many Caminos, so little time and my knees do not understand why I must do this again and again and again ). There was some hunting beginning in October, so the gun shots in the distance were a little unsettling especially when one is walking in tall corn.
If you're not walking all the way to Santiago, I'd try to miss August. Obviously hot, but lots of French vacationers too.
If you are going to Santiago, it may be necessary to start in August so you can finish before it gets too cold. I left Le Puy on August 17 and got to Santiago on October 28. It was hot a few days in August, but most of the weather was great. It started to get pretty rainy in Galicia at the end of October. I don't know if that's normal or not, but I'm glad I didn't push it even later.
I walked once in autumn, starting from Le Puy in mid September, and a second time in spring, starting late April. The weather was pretty good overall both times, but there were a few days of cold rain and even snow, on both walks. On the spring walk it got pretty hot towards the end, I can remember walking into Aire-Sur-l'Adour through treeless fields with a hot sun beating down.
I started Aug 20. There was a heat wave for a few days, but I didn't think it was too bad. Mostly the weather was perfect. I also enjoyed walking with all the French vacationers. I actually missed them in September when the crowds thinned out - not that there was ever a "crowd" like on the Camino Frances. There were actually some chilly mornings in September where I was glad that I had warmer clothes.
We walked from mid May 2018. Some wet days, a couple of thunderstorms then becoming hot towards the Pyrenees. It had been a very wet Spring there so some muddy tracks and a couple of flooded ones with road walk arounds. Beautiful scenery, lush and green, lots of wild flowers and fields of narcissus on the Aurbrac Plateau being harvested for the perfume industry. Seeing the cows all dressed up in their floral head dresses, tractors decked out with flowers and farmers in traditional coustume for the Transhumance was a real highlight in Nasbinals but be aware that accommodation can be scarce during these events - we had a long day that day.
Last week of August to first week of October, 2018. I recall some showers, and two full days of rain towards the end of September but the walk is so glorious I have only fond memories of those days. I'm only recalling one day where the heat was really getting to me (mid-Sept) at the end of the walking day. Yes, the first 10 days we were walking with many others, especially groups of French vacationers. After Conques, the numbers of walkers fell. Everyone we met (minus one French bicyclist) were memorable in the very best way possible. We booked 3-4 days ahead, as is the way in France, and never had difficulty finding accommodations. My very favorite walk!! Buen Camino~!!