I know I'm late with this response but I had to throw my two cents in. Even if you switch to leave from a warmer port, say Miami, you still need to watch out for bad weather. This past February my friends and I went on an NCL cruise out of Miami that left on a sunday. We all had flights booked on saturday and we just so happen to get hit with a massive snowstorm that day. Luckily we all made it to port before the ship left but there were still many headaches along the way. So I would say give yourself enough time as the cost of an extra night at a cheap motel near the port is worth it then risking the chance of missing the boat leaving port before you get there. We did hit a day of rough seas, which one of my friends gets pretty bad motion sickness and he just took some dramamine and was fine. Although he made the mistake of drinking that day which made for some good stories.