[dghlsakjg]

Your clock was off. Tides advance ~30 minutes per day. But not exactly 30 minutes. Sometimes more. Sometimes less. Sometimes it doesn’t follow a semi diurnal pattern.

Water can’t pass through landmasses, and that is a huge factor. If the earth had no landmasses, the tides would be entirely as you expect. However, if you look at a global visualization of tidal heights, you will see that a small landmass, NZ is a great example, can have highs and lows just miles apart. Same in Panama, what happens on the pacific coast is wildly different to what happens on the Caribbean.

In addition, the gravity of the sun comes to factor as well. Where I am, north of the 50th parallel, we simply don’t get very low tides during the day when we are near the winter solstice. The opposite happens in the summer.

The timing of the tides for any given spot tend to be predictable (where it is semi diurnal anyway, other places are a mess). But heights are extremely variable.

[TomK32]

And then there's the Solent which for Springs has a double high tide as the western end of the Solent is quite narrow and the tide racing around the Isle of White and in from the wider eastern side. https://www.nci.org.uk/solent-tides/

[kgwgk]

> Your clock was off. Tides advance ~30 minutes per day.

“roughly 12 hours”

[CommenterPerson]

Thank you. I still feel the stackexchange post misses the forest for the trees (and weeds). Take a look at the NOAA global map showing coasts that have semidiurnal tides (that is, one in roughly ~12 hours) [1].

Most all of the coast of Africa is semidiurnal. So is east coast of North America, a lot of South America. Bay of Bengal, a lot of Europe. If you see the map on the RWU [2] site it shows Greenland and the north coast of Russia (although stretched due to the latitude) are also semidiurnal. This is a major part of the global coastline. The simple mental model explains this. I feel that going to partial differential equations, fourier series, etc. etc. is a little too complicated.

[1] https://oceanservice.noaa.gov/education/tutorial_tides/tides... [2] https://rwu.pressbooks.pub/webboceanography/chapter/11-3-tid... -

[detourdog]

Wind can have a large effect the Chesapeake Bay's tides during large wind events in the atalanitc can effect water levels by feet.