Title text:
They're up there with coral islands, lightning, and caterpillars turning into butterflies.
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Source: https://xkcd.com/3135/
this post was submitted on 30 Aug 2025
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Been trying to learn about the tides around here so I can tell what I'm seeing on the water. Imagine my joy when I found a Casio, which I collect, with tide and moon phase indicators!
And that's when I learned the Gulf Coast is strange, has diurnal tides (twice a day) the watch can't predict. Took me an hour and a half to figure out it would never function. The moon phase works!
Huh. TIL that there are three common types of tidal cycles and which one you get depends on geography, location, ocean currents. https://beltoforion.de/en/tides/tidal_cycles.php
And yeah, dinural is apparently the most rare of the three. Wild.
Thanks. I didn't know either that there are places, where the sea level does not rise and fall twice a day.
I was reading Circe, by Madeline Miller, and on several pages some ancient Greeks wait for the tide to sail away, or watch the sea rising while waiting for Odysseus, and so on. Like, woman, did nobody notice at your publishing house?
Me, too, TIL!
Diurnal tides are once a day (semidiurnal is twice a day). By the Gulf Coast, I guess you must mean the Gulf of Mexico. I'm living on the other side of the world in the other diurnal region, so I assume our tides are synchronised!
Gulf of America, you extreme left Antifa socialist!!1!one
No idea how I got that backwards. I even looked it up before posting!
Diurnal bros! Theres's dozens of us!
Tidal prediction requires a harmonic analysis of observed tides, and its location specific. Not sure how a watch is supposed to do that other than holding a database of tidal coefficients.
This video contains a lot of interesting history of tidal analysis and prediction:
https://youtu.be/IgF3OX8nT0w
There are adjustments you can make on the watch. Requires tables and whatnot. That's why it took me so long to figure out it wouldn't work!
Tides go in, tides go out, you can’t explain that.
Casio can't!
Now if you want strange tides look at Southampton. Not very big tides given its in the middle of the channel but the graph is an interesting one to look at.