One question, please:
if I leave Irun october the 13th and will arrive in Finisterre approximately the third week of november, where can I check (if it's possible) the weather that I'll find, in advance, please?
If you're walking the Camino del Norte then you'll be walking through the northern coastal regions of Spain - so much of the weather will be dictated by what's happening at sea. You can definitely expect frequent rain during that time of the year. You'll also have some beautiful sunshine and great views too.
Last year the warm summer weather lasted until about 20th October, but so far September has seen significant drops in temperature and massive flooding on the Mediterranean coast - none of which fits with yearly average statistics.
It will be what it will be, all you can do is check ahead by asking locals, watching TV weather reports (usually called EL TIEMPO or METEO) or, if you have data on a smartphone, then you could use the app called Windy - this has live satellite data for rain, wind and temperatures and is pretty accurate most of the time.
Many people in Spain use the internet site
AEMET.ES for forecasting weather. I have a cousin here in the Spanish military and he uses this.
I've attached a link here, set on Irún but you can select any area or town etc.
Weather. Forecast for Spanish towns: Irun (Gipuzkoa) - 7-Day weather forecast - Table
www.aemet.es