What Are Tides & How Do They Occur
Tides refer to the falling and rising of ocean levels within a day, caused by the gravitational attraction of the sun and moon and the earth’s rotation.
(The sun’s gravitational force on the earth is only 46 percent that of the moon. Making the moon the single most important factor for the creation of tides.)
So this is what happens:
The earth/ocean gets pulled into a bulge one way by the moon’s gravity and into a bulge on the opposite side by the rotational force of the earth.
This in turn creates a bulge on either side of the earth. A bulge closest to the moon (gravity) and a bulge on the opposite side/farthest away from the moon (rotational pull)
So there are generally two high tides and two low tides in any given 24 hour period – the amount of time the earth takes to do a full rotation.
Keep this in mind though: By the time the earth has done one rotation, the moon has shifted 12° further, and it takes an extra 50 minutes for the moon to be in the same position at your local break. So, the tidal cycle is not 24 hours long, but 24 hours and 50 minutes. Because of this, high and low tides are about 50 minutes later every day.
So How Does The Sun Factor In?
In one month, the moon rotates around the earth. When the moon is between the sun and the earth (at new moon), the sun’s gravitational pull is in the same direction as the moon’s. During these days the high tides are higher and the low tides are lower than they’d be with just the moon’s pull alone. This is called spring tide.
The same thing happens when the moon is on the direct opposite side of the sun (full moon). The two gravitational forces work together to make high high tides and low low tides.
When the moon is in its first quarter or its last quarter, the sun’s gravitational pull is in perpendicular direction to that of the moon. The sun pulls water away from the areas of high tide to the areas of low tides, resulting in lower high tides and higher low tides. These are called neap tides.
So What Does All This Mean For a Surfer
Your local break more than likely will be affected by the tides, negatively or positively.
During a high tide there is more water on the reef, sand bank or point break etc. During low tide, less water on the reef, sand bank etc. Whether or not that makes your spot turn on or off only you can tell.
It takes lots of observation to get to know all the spots in your local area and know if they are good on a low, mid or high tide or if a low going high or high going low is good for a particular spot.