If you walk the Camino de Finisterre in September, you can expect generally good weather. This path passes through Santiago de Compostela, Negreira, Olveiroa, Corcubión, and ends in Fisterra. You'll see many days with some cloud cover, and it may rain lightly from time to time. Heavy rain is rare, which makes this a good time for the walk.
On this path, the daytime temperatures usually reach about 24-25°C - warm but not too hot. At night, it cools down to around 13°C. The temperatures stay fairly steady throughout the path.
Rainfall along the way is light, with more chances of rain when you start in Santiago de Compostela and finish in Fisterra. For example, it rains very little in Negreira, with only 0.3 mm on average, and a bit more in Corcubión with 1.5 mm.
In short, September is a good time to walk the Camino de Finisterre. You'll have warm days, cooler nights, and some rain.
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