The brightest moon in about 18 years with grace the skies Saturday night. The "supermoon", besides sounding really awesome, is roughly 30% brighter and 14% larger than a regular full moon.
The moon circles around the earth on an elliptical path. It's closest point on this path, under 222,000 miles, is called the Perigee. While there is nothing especially uncommon about either the Perigree or the Full Moon they hardly ever line up on the same day. When these two semi-monthly events line up they produce the brightest and biggest moon.
The moon will most precisely hit its Perigree at 3pm EST meaning Europe should actually see it at its true peak. It will diminish only so slightly however by the time the moon rises over the United States.
Though there will be plenty of light the "supermoon" will not have an especially strong impact on tides or produce strong swells, at least not any more than a perigree moon normally does.