Went to Alaska Sept 17-26, 2019, (a few years ago). Although every year can be different and September can always be unpredictable. The weather was great for us, one port day had rain (Juneau) but we brought rain gear and were fine. (bring a good light weight "water proof" rain jacket and maybe pants), We did the hike up at Mendenhall Glacier and had a great experience. All the other days were long sleeves and sweat shirt weather. Most of the port days were cloudy but not cold. They say to layer your clothes but I mostly just wore a long sleeve shirt and a sweat shirt, we were outdoors a lot hiking or just walking the streets and never got cold. September is a wonderful month to go to Alaska, (no bugs 🤗) and a bonus if you go this late is that everything in the shops are on sale because their season is ending. I got a great Alaska sweat shirt for only $10 and most of the souvenirs were all 50% or more off.
