In Catalonia, the weather is usually warm in early September with temperatures between 26°C to 31°C during the day and 17°C to 20°C at night. The weather can be sunny, partly cloudy, or sometimes rainy, but the rain is usually not heavy.
The weather is similarly warm in Aragon, with day temperatures around 29°C and night temperatures about 18°C. It's often sunny here, but it can sometimes rain a little.
When you reach Navarre by mid-September, the weather starts to get colder, with day temperatures falling to 20°C and night temperatures dropping to around 9°C. The weather is more unpredictable here and it can rain more often than in the other regions, but the rainfall is still usually not heavy.
To sum up, if you plan to walk the Camino Catalán in September, expect warm, usually sunny weather with some chances of light rain. Remember to take a raincoat, as rain is more likely in Navarre.
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