1. ## King Tide Question

Next week, we will have the highest predicted tide in Puget Sound for 2023 (13.1 feet). Interestingly, the low tide that day will not be lowest tide of the year. The lowest tide of the year will be in July (minus 4.0) but the high tide on that day will not as high as the January king tide.

How come?

2. ## Re: King Tide Question

Originally Posted by Bobcat
Next week, we will have the highest predicted tide in Puget Sound for 2023 (13.1 feet). Interestingly, the low tide that day will not be lowest tide of the year. The lowest tide of the year will be in July (minus 4.0) but the high tide on that day will not as high as the January king tide.

How come?
Not an easy answer, as it's a complex topic. For a full explanation, I highly recommend...

3. ## Re: King Tide Question

Variables caused by the juxtaposition of earth, sun and moon. And as Neil DeGrasse Tyson likes to point out, the earth’s water levels stay the same, we just rotate in and out of different depths.

4. ## Re: King Tide Question

Originally Posted by David G
Not an easy answer, as it's a complex topic. For a full explanation, I highly recommend...

I have read the book, based on your earlier suggestion. I just requested it from the library to re-read. Maybe I can find the answer.

I liked Neil DeGrasse Tyson's image that there is always a bulge under the moon and we rotate into the bulge and out of the bulge. It's an amazing thing when you think about it.

5. ## Re: King Tide Question

It’s easy to calculate… just incorporate the position of the moon and sun (37 different terms… because the orbits of the earth and moon are not circular) along with the data that describes the characteristics of the location you are trying to predict for (another 37 terms)… the height of the tide will be the cosine sum of these 37 terms.

…except for Anchorage AK… that one takes 117 terms

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## Re: King Tide Question

Going to the coast tomorrow. Should be splendid surf. Beware of sneaker waves!

7. The tilt of the earth puts any location in a different relative position depending upon time of year. Also, the earths distance from the moon and sun is different.

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8. ## Re: King Tide Question

Originally Posted by Dave Gray
Going to the coast tomorrow. Should be splendid surf. Beware of sneaker waves!
Son2 is there with his new gf... admiring the ocean and enjoying the tidal influences.

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## Re: King Tide Question

In a similar vein I was surprised some years ago that the latest sunrise, the earliest sunset and the shortest day were on different days.

Looking at the figures for London last month they were approximately latest sunrise 28th, the earliest sunset 12th and the shortest day 22nd.

10. ## Re: King Tide Question

Originally Posted by Bobcat
I have read the book, based on your earlier suggestion. I just requested it from the library to re-read. Maybe I can find the answer.

I liked Neil DeGrasse Tyson's image that there is always a bulge under the moon and we rotate into the bulge and out of the bulge. It's an amazing thing when you think about it.
But there is also always a bulge on the opposite side from the moon.

Tom

11. ## Re: King Tide Question

Tidal predictions take into account about 15 cyclical variables, combined by Fourier analysis.
The first mechanical analogue tidal predictor in the UK was:
One of Thomson's designs for the calculating part of a tide-predicting machine is shown in the figure (right), closely similar to the third machine of 1879-81. A long cord, with one end held fixed, passed vertically upwards and over a first upper pulley, then vertically downwards and under the next, and so on. These pulleys were all moved up and down by cranks, and each pulley took in or let out cord according to the direction in which it moved. These cranks were all moved by trains of wheels gearing into the wheels fixed on a drive shaft. The greatest number of teeth on any wheel was 802 engaging with another of 423. All the other wheels had comparatively small numbers of teeth. A flywheel of great inertia enabled the operator to turn the machine fast, without jerking the pulleys, and so to run off a year's curve in about twenty-five minutes. The machine shown in the figure was arranged for fifteen constituents in all.
https://en.wikipedia.org/wiki/Tide-predicting_machine

The 15 cyclical elements do not combine to a symmetrical up or down.

12. ## Re: King Tide Question

Wow - and that's not what he was famous for.....
https://collection.sciencemuseumgrou...tide-predictor

13. ## Re: King Tide Question

The key word is “prediction”. The actual tide levels are influenced by several other variables such as runoff and most notably atmospheric pressure. We have a very high predicted tide for Tuesday morning here. It is predicted higher than the one that did all the damage a couple of weeks ago. But then, there was heavy runoff from high freezing levels in the mountains and one of the lowest barometer readings I have ever seen at 28 point something. I doubt Tuesday morning’s highest predicted tide will be that high.

14. ## Re: King Tide Question

Another interesting factoid: Tide Prediction Machine #2 was used until the mid-60’s, but NOAA shifted to a Fortran program and punch card input after that. The Fortran program, including the use of punch cards, was still in use by 1994, when I discovered an error in the actual printed tide book produced annually by NOAA. I emailed them to point out the error, which they initially denied. After a number of back and forth emails, NOAA finally admitted I was right about the error, and they apologized to me for initially refusing to acknowledge the error.

The error, as it turned out, was caused by one punch card that had some data accidentally shifted to the right by 5 columns.

15. ## Re: King Tide Question

Was supposed to be this morning around 10am down in Truro. Fortunately no wind to speak of. The current crop of houses too close to the beach is safe for another month.

Last year this happened: