Every day, all over the world, the oceans experiences two high tides and two low tides. If you surf, snorkel, boat, paddleboard, or spend any time at the beach, you might have even checked tide reports for the day so you know what to expect (a great practice by the way). As the day drags on, the waters come and go. But why twice a day? Well, in short: it all has to do with the moon.
Our Earth has gravity, and therefore a massive gravitational field; it’s what keeps you from floating right off the ground into space. The moon also has a gravitational pull and, though smaller than ours, it effects how the ocean acts. The Earth rotates on its axis every 24 hours, like those toy globes with a pole through the top and bottom. Since the moon moves as well, tides are based on the “lunar day”, which is 24 hours and 50 minutes. This is why, occasionally, tide reports will only have 3 tides listed for the day rather than the normal four. The last tide of the day prior happens right before midnight, and the first tide of the next day occurs right after. The gravitational pull from the moon essentially squeezes the water around the globe, with the highest tide of the day facing the moon, the low tides on the sides, and the lower high tide away from the moon (image below).
Image Source: Maximum Weather Instruments, 2022