Tides are the sum of effects caused by the gravitational attraction of the Moon and the Sun, as well as the gravitational force here on Earth.
The Moon's gravitational force is equivalent to only 17% of the Earth's gravity; while the Sun affects about 46% of a force over the Earth. As it is so much closer, the moon is constantly attracting waters of the Earth.
When the Moon is in line with one side of the Earth, it pulls on the water, causing a high tide. Because the Earth rotates on its axis the moon completes one orbit in our sky every 25 hours. Thus, we see two tidal peaks - as well as two tidal troughs - roughly every 12 hours.
Since the Moon moves around the Earth, it is not always in the same place at the same time each day. So, each day, the times for high and low tides change by 50 minutes.
When the Moon, Earth and Sun are perfectly aligned, the sum of the gravitational pull of the Sun and Moon cause maximum tide, or extreme tides.
When the Moon lies between Earth and the Sun we observe a New Moon. When the Moon is on the opposite side of the Earth from the Sun, a Full Moon is visible. In both of these cases, tides are 20% lower and higher, respectively, than the usual tides.
The Guinness Book of World Records declared that Burntcoat Head, Nova Scotia has the highest tides in the world. The Bay of Fundy has a 17-meter (55.8 feet) tidal range.
In many surf spots, surfing is only possible in low and high tides, (when conditions such as determined swell and wind are right). On certain other waves, middle tide conditions can be the best time to hit the surf.
All of these variables can be considered along with ocean floor and shore geography in order to establish standard patterns for above-average surfing days.
Discover the tidal "Rule of Twelfths" in surfing.