Alaska weather is 'hit & miss'. We have cruised during the first part of May and had super weather. No rain. We did July a few years back and it rained the entire cruise. We are doing a mid-Sept. this year. BUT Alaska is so beautiful that the weather really does not effect our cruises. IMHO.....Just enjoy your cruise...whatever time you visit Alaska.....
I don't recommend anything past the first week of September- unless in a give away situation which Sept can be. The weather can greatly fall off as Sept gets later. I really like mid to late August- better wildlife viewing than Sept, longer days and still bargain rates. I haven't paid over $500 last 2 years for Sept cruising inside cruise only of course.
We have visited Alaska four times and believe that May is the best--we like the
white mountains and the beautiful glaciers. If you are into fishing, we were in
Ketichikan in August and the salmon were coming up the river for spawning--a
great sight--the river in the middle of town was "wall to wall" fish. The "best month"
depends on your individual expectations.
We had terrific weather for our June vacation. Land b/e June 6-16; and cruise June 16-23. But I understand the weather is extremely variable -- most of the Alaskans we spoke to seemed amazed at our run of good weather.
We were there July 14-21, 2001 and had no rain, except for a short sprinkle in Skagway. Just lucky. Some towns said it had rained for 11 days prior. We did however have great fishing and wildlife viewings during this time, which were important for us. The salmon attract alot of other wildlife, like bear and eagles. Also watch from your cruiseship in the "Icy Straits" going into and out of Glacier Bay and you might also see some great humpback whale sightings. Good Luck!