We took fleece jackets and that was fine. In Sitka we were a little cold, probably dressing in layers is the best bet. We did not have any rain. It was cool (60's or 50's), but not really cold.
Our first 24 hours we had high seas and everyone was a bit sea sick, some more than others. After that no problem. Sunday we got on the boat.
Next day was Glacier Bay, you don't get off the boat, I recommend going to the bow of the boat for best views.