Alaska Weather In September 2025. Expect 12°c daytime maximum temperatures in the shade with on average 4 hours of sunshine per day in juneau in september. Don't forget a sweater and light or normal jacket, but also pack light clothing in case.

Don’t forget a sweater and light or normal jacket, but also pack light clothing in case. September in alaska is the shoulder season—offering the promise of lower prices on hotels and excursions, fewer crowds and bugs, fall colors, and northern lights viewing.