In Seattle we experience two high tides and two low tides every day, but what causes them?

Gravity, mainly by the moon (but helped by the sun). The moon excerpts a gravitational pull on Earth’s water and Earth, which results in the Earth actually being pulled away from its water. This gravitational phenomenon is enhanced by the sun. When everything (moon, Earth, sun) is aligned (full moon and new moon) we experience spring tides (strong). When the moon is not aligned we experience neap tides (weak).

In Seattle we have mixed semidiurnal tides— which means the high tides are different volumes, the low tides are different volumes (mixed) and both occur twice a day (semidiurnal).

Really low tides occur during the day in the summer and during the night in the winter.

Around the world we have amphidromic points in the oceans. These points are tidal nodes where no tides exist. The further away you are from an amphidromic point the the larger the tides can be. But tidal magnitude also depends on bathymetry (sea floor), geography, and currents.

Check out tidesandcurrents.noaa.gov to find more information about tides in your area!