Does Huixian County in Longnan need to wear a thin sweater in September?

No need. According to the meteorological information of Huixian County in Longnan, the weather in Huixian County in Longnan gradually turned cold in September and entered the autumn climate. The average temperature is 7 to 14 degrees Celsius. You can wear a suit, coat, windbreaker, etc. You can wear a thin sweater when the weather is colder. Therefore, in Huixian, Longnan, you don't need to wear a thin sweater in September.