I go ocean fishing almost every weekend and part of how I plan my excursions is by checking the tides. I live in Long Beach, CA and the tides are always semi-diurnal. Two low tides and two high tides every day.
But this coming weekend, the tides in my area are messed up. On Saturday, there’s a high tide at 5:15am, then a low at 8:00am. Then a high at 2:34pm and the final low of the day at 10:47pm.
In other words, high tides are 9 hours apart but low tides are almost 15 hours apart, which makes sense in one way because 9+15=24, but the part I don’t get is why are high and low only three hours apart in the morning but nine hours apart in the afternoon/evening? Again, 9+3=12 (or half of 24) so that part of the math sorta makes sense, but I don’t see how it happens.
The relative positions of the Earth, Moon and Sun don’t change much in one day and the Earth is rotating at a constant speed, so why isn’t the afternoon pattern the same as the morning pattern but just 12 hrs later?
There has to be something obvious that I’m not seeing.
I was curious, so I went googling and found this on the wikipedia article on tide clocks:
[QUOTE=wikipedia]
However, in other parts of the world such as along the Pacific Coast, tides can be irregular.[1] The Pacific Ocean is so vast that the moon cannot control the entire ocean at once. The result is that parts of the Pacific Coast can have 3 high tides a day.
[/QUOTE]
Large bodies of water have substantial inertia, and are subject to various forces and constraints (coastlines, straits etc). This creates interference patterns that result in sometimes complex tides.
The pattern for Long Beach seems to be mixed semidiurnal, at least at neap tides. That is, there are two lows and two highs per day, but one low is much lower than the other. This is probably because there is some sort of diurnal harmonic that counters one of the low tides, such that it isn’t as low as would otherwise be expected.
Princhester covered most of it, and while I know that posting links to videos is typically taboo on the dope I have no practical way to explain that you have probably had how tides work explained in a way that is not true.
A wall of text cannot describe how they work as well as this video does.
You should look at the tides up here on the the Salish Sea if you want to see how crazy things can get.
The Torres Strait in Far North Queensland is the meeting of two oceans through a narrow strait with the ocean on one side up to 0.5m lower than the other, and the tides are diurnal on one side and semi-diurnal on the other. In the Strait it’s anyone’s guess what the hell is going to happen exactly and marine pilots taking large ships (with less than 0.5m under keel) through have to use buoys transmitting water heights in real time to know how to time their run through the Strait.
I should have qualified that I was talking relative to California Coastal tides. We do have some areas that exhibit the same diurnal on one side and semi-diurnal difference just miles apart. Deception pass is the most extreme for currents here with ebb and flood tide current speed of around 8 knots.
But it probably depends on what your in too, the 3 knots by cattle point is a bigger deal in a 40’ sailboat with a ~5 knots average max speed under typical airs. But yes it is manageable, you just have to wake up at 3AM to make a passage some times.
As every boater in the area has both the Canadian and US almanacs and flip books I cannot find an example on line, but the following site will animate the fun, unfortunately they also limit the data points if you zoom out.
But yes, any place that has restrictions will have similar cases. Here it is 6800 square miles of water flowing in and out of the 10 mile wide Strait of Juan de Fuca that requires you to look at tides and current predictions at multiple points along the route.
Wow. You have a low tide less than 3 hours after high tide? That is really strange. Here in NJ time between tides is roughly 6 hours as are your next tides in OP.
Tides in the Gulf of Mexico are pretty weird too. Lots of sloshing and bottom effects mean the simple [two bulges following Sun & Moon] model is all but irrelevant.
Tides can vary quite a bit from the nearly twice-a-day norm. The intro to the tide page on Wikipedia even mentions one-a-day tides that occur in some places. And that’s just the start.
There can even be places in the open ocean that experience no tides at all. It’s like one of those sandwich cutting theorems from Math. If someplace has tides with one phase and another place has tides with the opposite phase, then somewhere in-between there’s a place with no phase.