No way to tell. Alaska weather is all over the board, just like the Caribbean. Last year we had temps in the high 40's to mid 50's on our late June cruise. The cruise immediately prior to ours had temps in the 60's and low 70's.
You just have to go prepared for anything. Clothing that can be layered. We also brought collapsible umbrellas that are about 8 inches long when closed up.