My Seattle body has the same problem, and started in SJPP the 2nd week of September last year to beastly temps. But if you start by say 6 you can get in 6 hours of walking by noon, which is grand because the real heat starts to build up after...
I'm in León and it feels hot in the afternoon (siesta time!).
Most people are starting walking at 5.30am, 6am or 6.30am in order to get most of the walk done before it gets hot.
I have been starting at 7am and doing 20km or so per day.
The good...
We are starting the CF in St Jean DPP in 3 weeks' time. The weather aps forecasts for next 10 days time are showing very high temperatures (well very high for our Irish bodies!) around both St Jean and Pamplona.
What is it actually like there...
Have a look at public transport options on Google maps or Rome2Rio apps. Google maps says there's an ALSA bus at 13.45 (destination Pamplona) that will take you there.
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