Just general surfing stuff

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Hatchnam
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Re: Just general surfing stuff

Post by Hatchnam » Thu Aug 23, 2018 3:41 pm

SAsurfa wrote:
Thu Aug 23, 2018 1:30 pm
Wow what have I just read :o

Kilojoules for wave forecasting.. a product of period and open ocean swell height which generally get incorrectly combined if there's multiple swells from the same angle or similar periods.

It's jiberish and looking at Sydney today KJ's are 261 but south facing beaches are overhead, doesn't line up Cranked..

You'd just found a way to correlate the KJ to size on your coast which generally sees swells rise and fall without too much contamination.

I'd guarantee it would totally muck up the forecast for a large long-period groundswell which has fore-runners arriving a day before, followed by the bulk of the swell.

Leave the Kilojoules for those talking about the consumption and burning of energy.
thank god you arrived to shut this nonsense down
godsavethequeen wrote:
Thu Nov 14, 2019 11:55 pm
My beef has always and only been with the realistic range available to the average Sydney working stiff
steve shearer wrote:full dionysian hand jive body torque

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Cranked
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Re: Just general surfing stuff

Post by Cranked » Thu Aug 23, 2018 3:55 pm

SAsurfa wrote:
Thu Aug 23, 2018 1:30 pm
Wow what have I just read :o

Kilojoules for wave forecasting.. a product of period and open ocean swell height which generally get incorrectly combined if there's multiple swells from the same angle or similar periods.

It's jiberish and looking at Sydney today KJ's are 261 but south facing beaches are overhead, doesn't line up Cranked..

You'd just found a way to correlate the KJ to size on your coast which generally sees swells rise and fall without too much contamination.

I'd guarantee it would totally muck up the forecast for a large long-period groundswell which has fore-runners arriving a day before, followed by the bulk of the swell.

Leave the Kilojoules for those talking about the consumption and burning of energy.
Why? They are useful. If they are not useful for you thats fine by me.

Here's a few points in reply though:

In regard to swells

1.There are usually a combination of various swells at any one time where I surf: WSW, SW, SSW, S and SE with periods from 6 to 22

1. I'm pretty sure the kJs are calculated from the swell height and period of the significant waves of the predominant swell, so saying the forecast kJs are incorrect is the same as saying the swell height and/or period for the predominant swell are incorrect.

In regard to kJs

1. Swells of various heights and periods can have the same energy (kJs)

2. As the swells move into shallow water their period and and height changes but their energy remains (largely) the same

3. The only advantage of being familiar with the kJs is that you don't have to know how each of the infinite combinations of swell height and period for a specific number of kJs presents as breaking waves at your local. If its the same number of kJs then it will produce very similar breaking waves.
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Thud
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Re: Just general surfing stuff

Post by Thud » Thu Aug 23, 2018 4:04 pm

Let it go mate.
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SAsurfa
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Re: Just general surfing stuff

Post by SAsurfa » Thu Aug 23, 2018 5:03 pm

Cranked wrote:
Thu Aug 23, 2018 3:55 pm
so saying the forecast kJs are incorrect is the same as saying the swell height and/or period for the predominant swell are incorrect.
Yes, I'm saying the models get this wrong plenty of times and this is when you'll get a wrong forecast.

Tomorrow for example, we've got an existing SW swell across Bali, and then there is a large new long-period groundswell due to arrive through the morning, peaking into the afternoon.

Now the models incorrectly combine this new long-period energy with the existing swell and jump the forecast size by midday on our Swellnet models and by 8am on your forecasts.

This is wrong and we'll actually see the swell build strongly through the morning and peak later in the day/overnight...

1.7m @ 18.3s and 1.8m @14.6s combined incorrectly at midday and over-forecast.
Image

Similar to Surf Forecast.com but at 8am with energy jumping to 3832Kj.. when peak will be later when the model has 2900..
Image

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Cranked
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Re: Just general surfing stuff

Post by Cranked » Thu Aug 23, 2018 5:04 pm

Sorry, that one was just crying out for a reply, I couldn't resist :-D-:
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Hatchnam
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Re: Just general surfing stuff

Post by Hatchnam » Thu Aug 23, 2018 5:32 pm

Craig, Can we also see a smack down on magic seaweeds forecasting shenanigans for east coast Australia .
godsavethequeen wrote:
Thu Nov 14, 2019 11:55 pm
My beef has always and only been with the realistic range available to the average Sydney working stiff
steve shearer wrote:full dionysian hand jive body torque

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Cranked
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Re: Just general surfing stuff

Post by Cranked » Thu Aug 23, 2018 6:37 pm

SAsurfa wrote:
Thu Aug 23, 2018 5:03 pm
Cranked wrote:
Thu Aug 23, 2018 3:55 pm
so saying the forecast kJs are incorrect is the same as saying the swell height and/or period for the predominant swell are incorrect.
Yes, I'm saying the models get this wrong plenty of times and this is when you'll get a wrong forecast.

Tomorrow for example, we've got an existing SW swell across Bali, and then there is a large new long-period groundswell due to arrive through the morning, peaking into the afternoon.

Now the models incorrectly combine this new long-period energy with the existing swell and jump the forecast size by midday on our Swellnet models and by 8am on your forecasts.

This is wrong and we'll actually see the swell build strongly through the morning and peak later in the day/overnight...

1.7m @ 18.3s and 1.8m @14.6s combined incorrectly at midday and over-forecast.
Image

Similar to Surf Forecast.com but at 8am with energy jumping to 3832Kj.. when peak will be later when the model has 2900..
Image

You state:
Now the models incorrectly combine this new long-period energy with the existing swell and jump the forecast size by midday on our Swellnet models and by 8am on your forecasts.
but Surf Forecast is not combining the two swells, the big jump at 8am from 2031kJ to 3832kJ is because the long period 18s swell jumps from 1.7m to 2.5m (shown on both surf forecast and swellnet).

The open ocean swell height has only gone up by about one third but this means the energy nearly doubles (roughly 2000 to 4000), its nothing to do with the other 15s swell. This is another reason why swell energy is a better measure of an open ocean wave than wave height and period.

If the swell forecast is correct then the breaking waves will be much bigger around 8am.
Last edited by Cranked on Thu Aug 23, 2018 6:46 pm, edited 1 time in total.
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Re: Just general surfing stuff

Post by Hatchnam » Thu Aug 23, 2018 6:45 pm

Are you really going to argue with someone that forecasts professionally for a living?
godsavethequeen wrote:
Thu Nov 14, 2019 11:55 pm
My beef has always and only been with the realistic range available to the average Sydney working stiff
steve shearer wrote:full dionysian hand jive body torque

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Cranked
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Re: Just general surfing stuff

Post by Cranked » Thu Aug 23, 2018 6:49 pm

Can't you see I am pointing out what appear to me to be inconsistencies in what he has stated?

I'm quite happy to be corrected if I'm wrong. Maybe he is saying that the underlying model itself for the 8am swell height for the 18s swell actually includes the 15s swell and the model is incorrect? I'm not sure.

The best way to learn is to take a position as you see it and then see what happens.
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Re: Just general surfing stuff

Post by steve shearer » Thu Aug 23, 2018 8:30 pm

Cranked wrote:
Thu Aug 23, 2018 3:55 pm



2. As the swells move into shallow water their period and and height changes but their energy remains (largely) the same


Incorrect.
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Cranked
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Re: Just general surfing stuff

Post by Cranked » Thu Aug 23, 2018 9:47 pm

When the water depth is 1/20th of the wavelength the wave speed slows with decreasing water depth. As one wave slows, the wave following it moves closer. The wave speed and wave length decrease but the wave period and wave energy remains the same and the wave height increases.
Yep, incorrect for period, but correct for energy and height, which are the most pertinent for what I am saying
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Re: Just general surfing stuff

Post by Beanpole » Thu Aug 23, 2018 10:55 pm

Hatchnam wrote:
Thu Aug 23, 2018 6:45 pm
Are you really going to argue with someone that forecasts professionally for a living?
Professional witch doctor?

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SAsurfa
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Re: Just general surfing stuff

Post by SAsurfa » Fri Aug 24, 2018 8:20 am

That's what I'm pointing out Cranked, that jump is not natural and not what you'll see in real life, it's the models incorrectly combining the swells which I've learned to identify easily.

This is also why those who look at just windguru etc and see 18s swell arriving with no size, but with an existing 2m swell say the forecast is wrong when they think it should be falling out of the sky. And then the next day it's large and they say the swell running a day late.

It's not running late it's just you have to really aware of what's happening with the model output and in the real ocean to understand the actual expected sizes and timing.

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Re: Just general surfing stuff

Post by offshore1 » Fri Aug 24, 2018 11:06 am

Pay attention Grasshopper.

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Thud
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Re: Just general surfing stuff

Post by Thud » Fri Aug 24, 2018 3:52 pm

I just watched the replay of the Chopes final. God I hated watching that Charlie cnt carry on in the channel.

Medinas boards always look good though
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Re: Just general surfing stuff

Post by Thud » Fri Aug 24, 2018 4:49 pm

Bummer. Just saw the fella who lived in his van and surfed at Avalon drowned. Leggie caught on reef.
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Re: Just general surfing stuff

Post by Cranked » Fri Aug 24, 2018 5:15 pm

offshore1 wrote:
Fri Aug 24, 2018 11:06 am
Pay attention Grasshopper.
I have carefully noted the circumstances of this model failure offy and will treat any future occurrences with great skepticism
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Re: Just general surfing stuff

Post by Cranked » Sat Aug 25, 2018 6:54 am

SAsurfa wrote:
Fri Aug 24, 2018 8:20 am
That's what I'm pointing out Cranked, that jump is not natural and not what you'll see in real life, it's the models incorrectly combining the swells which I've learned to identify easily.

This is also why those who look at just windguru etc and see 18s swell arriving with no size, but with an existing 2m swell say the forecast is wrong when they think it should be falling out of the sky. And then the next day it's large and they say the swell running a day late.

It's not running late it's just you have to really aware of what's happening with the model output and in the real ocean to understand the actual expected sizes and timing.

Craig, if as you say, your swellnet model is also incorrect because of this anomoly, and you can recognise the model anomaly easily, this seems to indicate that the factors involved may be sufficient to enable you to code up a patch to recognise and correct the discepancy and modify the swellnet surf forecast appropriately?
“I don’t necessarily agree with everything I say ”— Marshall McLuhan

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