Best advice is to avoid anchorages that are exposed to a north swell even if they are calm when you tie up in late afternoon (CGB and White Bay, JVD are notorious and from the cruising guides & chart briefings this should be common knowledge). With the multiple sources of marine forecasts available at our fingertips there is plenty of advance notice available, and the swell can sometimes very quickly build in just a few hours. There are several good close-by alternatives to CGB and White Bay if a north swell is forecast - Great Harbour, Little Harbour, and Diamond Cay at JVD, and Sopers Hole.