Specific to John Ladds, comments on his Yosemite hike, I can verify the issue of hot temps in September.?
Our recently scheduled labor day hike from Kearsarge to OV was canceled due to the fire/smoke. We had a "back-up" plan last week to do the Grand Canyon of Tuolumne starting out of Yosemite Creek, exiting White Wolf. Unfortunately, I have a leg injury that precluded me from doing that back-up hike. My party went ahead with the back-up hike, but reported temps in the mid 90's almost everyday. (no water issues though).
I guess my take-a-way here is that for the higher altitude JMT hikes, I have found September to be great temps wise. This year, water availability is an issue for sure. Personally, any late season hike this year would revolve around proven availability of water. For the Yosemite hike and the lower elevations like the Tuolumne / Glen Aulin area, it's still pretty hot in Sept so kicking those hikes into October makes sense, and water availability is good. Obviously, with winter around the corner, any October hike is contingent on weather conditions.?
Will Cronan