Ocean tides are caused by the gravitational pull of the Moon and Sun. Due to the rotation of the Earth, locations will experience two high and two low tides each day. An alignment of the Sun and Moon will result in more extreme tides, known as spring tides.
High tides are caused when the moon is either directly overhead or when it is located on the far side of the Earth. When the moon is 90 degrees from a location, a low tide will occur. The rotation of the Earth means that coastal areas will see tides of both types twice each day.