I recently got off a Celebrity cruise throughout the Baltics & Scandinavia. Before my cruise, I made a weather chart for my wife and I to track the 10 day forecast across all ports on one page. I shared it with some other members of my cruise and everyone found it to be very helpful. I decided to make a website that generates the same report for other cruises which you can find here: Cruise Weather Forecasts - CruiseOutlook.com
The 10 day forecast is updated daily so as you get closer to your cruise, the information will be more and more relevant.