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Topic Title: How long does it take?
Topic Summary: From da 20 mile buoy
Created On: 07/26/2022 05:57 AM
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 07/26/2022 05:57 AM
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long_flaco1

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Good morning 2nd light fam.. I was discussing this with a random surfer at dawn yesterday while waiting on the next set..

How long does it take for waves to reach our coast in Brevard after they have hit the 20 mile buoy?

I was trying to find the mathematical calculations on my own but am coming up blank.. I "think" it would normally be about 3 hours with our typical 7 to 12 second swell period but, please put me on OG's?

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SK8 AND DESTROY
 07/26/2022 06:12 AM
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dingpatch

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Swell period is not a good indicator of "swell speed". For our purposes, our Atlantic swells are generally slower than in the Pacific, , , ,. A good rule-of-thumb is a speed of 15 MPH, maybe up to 17 MPH ?? Perhaps even slower ?

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 07/26/2022 06:21 AM
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johnnyboy

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I know they slow as they reach the shallower water so it's not a constant.

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 07/26/2022 06:24 AM
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dingpatch

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Yes, they start "dragging" on the bottom a long way out from shore.

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 07/26/2022 06:41 AM
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tom

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It takes a few months. Check again in Sept / Oct.

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 07/26/2022 07:40 AM
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ncsurf

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Originally posted by: dingpatch Swell period is not a good indicator of "swell speed". For our purposes, our Atlantic swells are generally slower than in the Pacific, , , ,. A good rule-of-thumb is a speed of 15 MPH, maybe up to 17 MPH ?? Perhaps even slower ?
That first sentence is very wrong.
 07/26/2022 08:23 AM
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Central Floridave

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120 mile buoy seems on average about 6 hours. I'm sure a lot of different factors. Angle, period, amplitude.

20 miler is usually within a couple hours. 1 mile buoy is currently not working unfortunately.

East Hatty buoy on a NE swell is typically 24 hours. E and SE Bahama Buoy about the same.

I'm not a detail oriented person so a OCD math nerd can give more accurate numbers! Just my experience.

 07/26/2022 10:02 AM
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long_flaco1

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Thanks Gents!

20 years on my comeback to surf-life and I'm "just now" starting to get it!

This here has been my missing piece of the puzzle and I've been forced into learning it (stoked for it too!) cause of soooo many conflicting surf forecast! Shoot just yesterdays Monday morning 2 out of 3 forecasters were saying said DONT GO, it will be shit! I saw the 20 miler showing 2.3 feet @ 9, and decided OUR BUOY'S DONT LIE to us!!!! and man, I had a super fun session (twas my bday and it has ALWAYS been about shin high historically)

Thanks for sharing this knowledge and stoked 2ndlightsurf community

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SK8 AND DESTROY
 07/26/2022 10:29 AM
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dingpatch

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ncsurf, Yep! Other than that locally we are not talking about "deep water" swells, , , , ,

From Surfline:

The speed of travel of the deep water swell group will be 1.5 times the swell period; ie: a 20 second swell will be traveling at 30 Nautical mph. The actual individual waves will be traveling at three times the swell period, so a 20 second swell will have waves moving at up to 60 Nautical mph.

The individual waves will travel to the front of the set as the swell group moves forward; once there, it'll slow down and drift to the back of the pack before moving forward again. Think of it as a conveyor belt turning at 30mph but the whole conveyor belt chassis is actually on the back of a flatbed truck going down the highway at 30mph. So if you had an object attached to the conveyor belt - while it's turning and being carried by the truck - the actual speed of the object would be 60mph. (Sound like math yet?)

https://www.surfline.com/surf-...0%3D%201%2C024%20feet.

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Edited: 07/26/2022 at 10:41 AM by dingpatch
 07/26/2022 01:10 PM
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surfsail

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Here in CFL we def have the 'continental shelf' effect going on ways - outside Bahamas , and north to NC, slowing the speed - and more than 'locally'..

If you are looking estimating arrival times of far off canes or Nor Easters far away near deep ocean depths & speeds are a good guesstimate.. Longer periods (far away swell source) def travel faster..

Longer period, smaller, 'pre-runners' come first, then typically period decreases, but size increases - till ... all gone..

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 07/26/2022 02:00 PM
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dingpatch

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Interesting part of Surfline link (above) in regard to the depth of a swell's "drag (especially off Brevard and further North):

Just how far underwater a swell's motion goes depends on swell period. That depth in feet is calculated by squaring the swell period then multiplying the product by 2.56. In the case of a swell with 20 second period, the math is 20 x 20 = 400, 400 x 2.56 = 1,024 feet. So that swell would begin to drag on the seafloor once it moved into waters of that depth. As the sea became shallower, the drag would increase. In contrast, a swell of six second period would not start to feel the resistance of the seabed until it entered seas that were 92 feet deep. Interference with the seafloor can change a swell's direction, in some instances up to 180 degrees. That wrap is much more pronounced in long-period swells than in short-period ones. So knowing a swell's period can be critical in forecasting if the swell will head straight into the coast or whether it will take a detour along the way.

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 07/27/2022 08:12 AM
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long_flaco1

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Good stuff guys! Thanks

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SK8 AND DESTROY
 07/27/2022 01:00 PM
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Cole

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Originally posted by: tom

It takes a few months. Check again in Sept / Oct.


via GIPHY





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 07/30/2022 01:27 PM
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SurfCaster

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If it's on the 20 miler it's pretty much on the beach. As Dave said 6hrs or so from the 120

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 07/31/2022 07:42 AM
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ncsurf

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Originally posted by: SurfCaster If it's on the 20 miler it's pretty much on the beach. As Dave said 6hrs or so from the 120
Depends on the period. Most of the time, it is going to be longer than that. But when you consider the time it takes to collect and then display the data on NDBC (or whatever site you use to see the observations), it is probably around that, again depending on the period.
 08/01/2022 07:42 AM
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SurfCaster

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I'm thinking it depends on the period.

It also depends on what you mean by "waves"....small amplitude forerunners may reach the beach with little to no discernible indication on the buoy (except maybe on the PSD). Furthermore, nobody really cares about 5 sec wind swell, and around here anything longer than about 13 sec interval closes out. So I'll stick with a rough guesstimate and surf checks, and you mathematicians can crank up Univac and time your paddle out down to the minute.

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"If I say it's safe to surf this beach, captain, then it's safe to surf this beach!"
 08/01/2022 07:49 AM
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StirfryMcflurry

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2nd Light math types in action
 08/02/2022 01:16 PM
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ncsurf

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Originally posted by: SurfCaster I'm thinking it depends on the period. It also depends on what you mean by "waves"....small amplitude forerunners may reach the beach with little to no discernible indication on the buoy (except maybe on the PSD). Furthermore, nobody really cares about 5 sec wind swell, and around here anything longer than about 13 sec interval closes out. So I'll stick with a rough guesstimate and surf checks, and you mathematicians can crank up Univac and time your paddle out down to the minute.
Some surfcaster you are! I'll be in the water waiting for you since I actually know how to read the buoys. ha!
 08/02/2022 01:56 PM
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long_flaco1

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I get what your putting down man!

My real mission is that there have been like SOOOOOOOOOOO many "Conflicting Surf Forecast" recently, that I'm completely over relying on these said surf forecast gurus hypothesis's and have been digging DEEP into the buoy data readings AFTER my sessions to see what it was saying when I first arrived and also when I left.. It's pretty dope to learn.. I really appreciate all of you 2ndlight familias input homies!

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SK8 AND DESTROY
 08/06/2022 02:18 PM
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SurfCaster

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Originally posted by: ncsurf

Originally posted by: SurfCaster

I'm thinking it depends on the period.



It also depends on what you mean by "waves"....small amplitude forerunners may reach the beach with little to no discernible indication on the buoy (except maybe on the PSD). Furthermore, nobody really cares about 5 sec wind swell, and around here anything longer than about 13 sec interval closes out. So I'll stick with a rough guesstimate and surf checks, and you mathematicians can crank up Univac and time your paddle out down to the minute.


Some surfcaster you are! I'll be in the water waiting for you since I actually know how to read the buoys. ha!


Sweet, prove it! Next pumping swell give us your dead nuts arrival prediction for Jetty Park then paddle out there and wave to the camera at the appointed time.

Flaco, you should be able to find sources on the internet like the Surfline link above. And although open ocean wave speed does depend on the period, the timing of swell arrival at your beach depends on a host of other factors like the characteristics of the fetch, direction, bathymetry, interference with other swells, currents, tides, etc. Its not something that can be solved with an equation, lab, or computer model. Some folks keep a surf journal which can be a big help and is kinda fun. Good luck, and remember it's better to be too early for the swell than too late!

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"If I say it's safe to surf this beach, captain, then it's safe to surf this beach!"

Edited: 08/06/2022 at 02:36 PM by SurfCaster
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