I believe it could if circumstances are such that a port stop is unsafe and there is nowhere else to go. Whether any penalty against the cruiseline would be waived for that I don't know. But extending one cruise means shortening -- or even cancelling -- another, so they try to avoid it but it does happen.
Why?
Weather, according to info posted on other forums. If you look at the top right corner of the image posted above your post, there seems to be an organized system close to what would be, and heading toward the UK. I looked at a few marine forecasts and there are gale warnings for today and potentially rougher seas to the north later this week...
Rough seas/ weather
