Wave models

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BA
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Re: Wave models

Post by BA » Wed Sep 19, 2018 6:51 am

I imagine ‘boo saying that in his stern dad voice.
Everything happens for a reason. Sometimes the reason is you’re just a stupid cunt.

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crabmeat thompson
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Re: Wave models

Post by crabmeat thompson » Wed Sep 19, 2018 6:57 am

BA wrote:
Wed Sep 19, 2018 6:51 am
I imagine ‘boo saying that in his stern dad voice.
wearing a lace teddy and suspenders.
steve shearer wrote:
Sat Mar 03, 2018 8:31 am
You are both absorbing salt and urinating.

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Cranked
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Re: Wave models

Post by Cranked » Wed Sep 19, 2018 7:02 am

alakaboo wrote:
Tue Sep 18, 2018 10:56 pm
Cranked wrote:
Tue Sep 18, 2018 9:37 pm
And as I've pointed out before, kJs are very useful and I use them as, unlike swell height, kJs remain the same irrespective of whether a wave is a deep ocean swell, near coastal swell, or a breaking wave
Jesus fcuk.
Your attachment to kJ doesn't even adhere to the laws of physics now?

So all breaking waves are silent, because none of the energy gets converted into sound, and there's never any erosion or acretion?
And waves all break the same way, regardless of bathymetry, because friction has no effect?

Just stop it.
You know what I mean boo', you are just being pedantic.

Of course the wave energy degrades while travelling in the open ocean, when affected by adverse wind and currents, when it encounters drag in shallow water (which can be 1000' for long period waves), by shoaling, and is dissipated quickly when it breaks.

Roughly though, wave energy is conserved as it enters shallow water but the wave height changes significantly as the wave length decreases, and more so just prior to breaking.

Compared to wave energy, wave height is a particularly bad choice to meaningfully describe any given swell.
“I don’t necessarily agree with everything I say ”— Marshall McLuhan

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Re: Wave models

Post by alakaboo » Wed Sep 19, 2018 7:19 am

Pedantry is the bedrock of science.

If you're fine with just disregarding all the situations where the real world doesn't match the theory, you should've been an economist.

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Cranked
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Re: Wave models

Post by Cranked » Wed Sep 19, 2018 7:22 am

Fcuking sound for Christ's sake! Very funny 'boo - there goes .00000000000000000000001% of the wave energy right there.
“I don’t necessarily agree with everything I say ”— Marshall McLuhan

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Re: Wave models

Post by alakaboo » Wed Sep 19, 2018 7:44 am

You disregarded gravity, for fcuks sake.

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Re: Wave models

Post by Drailed » Wed Sep 19, 2018 8:07 am

crabmeat thompson wrote:
Wed Sep 19, 2018 6:57 am
BA wrote:
Wed Sep 19, 2018 6:51 am
I imagine ‘boo saying that in his stern dad voice.
wearing a lace teddy and suspenders.
Yanking on his ball bag with one hand and thumbing his anus with the other.
Trev wrote:I have always had a lot of time for Dick
smnmntll wrote:Got one in the mouth once, that was pretty memorable

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Re: Wave models

Post by alakaboo » Wed Sep 19, 2018 8:21 am

As long as you aren't imagining me in the bath, loof.

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Cranked
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Re: Wave models

Post by Cranked » Wed Sep 19, 2018 10:13 am

alakaboo wrote:
Wed Sep 19, 2018 7:44 am
You disregarded gravity, for fcuks sake.
And gravity.

The issue I'm talking about is illustrated by Surflines predictions for yesterday at Ulus. They were saying the near shore swell was around 2m, and the surf was around 3m.

Surf Forecast just gives the near shore swell (2m in this instance) and kJs. I use the kJs for the reasons I have outlined above.

I'm not really concerned about the degradation of a swell over its lifetime and its causes, just the last 10 or so kilometres where it's feeling the change in depth and it's transitioning to a breaking wave.

I assume the swell models would have taken into account all the swell degradation factors up to that point anyway.
“I don’t necessarily agree with everything I say ”— Marshall McLuhan

bobjs
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Re: Wave models

Post by bobjs » Wed Sep 19, 2018 12:20 pm

I looked at the forecasts last night for yesterday arvo and they were both about the same, except for the arrival of the new swell.
Surfline and surf forecast were forecasting an open ocean swell of around 1.6m@14 seconds (at -9, 115 for Surfline).
Surfline also provided an estimated wave height based on that swell for Ulus of around 2.5-3m (actual not Iggy).
Last edited by bobjs on Wed Sep 19, 2018 4:42 pm, edited 2 times in total.

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Cranked
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Re: Wave models

Post by Cranked » Wed Sep 19, 2018 12:50 pm

Yeah, I realised this morning that my comment about Surfline overcalling the breaking waves was because I was comparing Surf Forecasts near shore swell with Surflines "breaking waves".

From experience Surf Forecasts kJs were telling me that but I was waylaid by the extra swell height data and lack of familiarity with the Surfline site.
“I don’t necessarily agree with everything I say ”— Marshall McLuhan

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godsavethequeen
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Re: Wave models

Post by godsavethequeen » Wed Sep 19, 2018 11:14 pm

OK so Nick seems not to remember the date of his recent Monday epic. No bother, I will simply delve into the search using some key words and then trip the light fantastic through the magicseaweed archive.

First up, 'North Wall':
buddy wrote:
Tue Nov 01, 2016 7:00 pm
20 blokes out north wall in onshore 2-3ft this arvo. I'll wait till it's pumping I think.
Have to say most of the people I speak to aren't living in fear though.
Magicseaweed forecast for 3pm: 2-3ft and onshore
Hatchnam wrote:
Thu Dec 24, 2015 11:44 pm
North wall Ballina was about 3-4 and building but a washy mess.

Image
Magicseaweed forecast for 3pm: 3-5ft, strong cross-onshore

Let's try 'Maroubra'
Hatchnam wrote:
Fri Aug 31, 2018 11:29 am
Maroubra. 2-3 foot. Washy mix of dying south swell and sorta building north east swell. Semi clean and still a few ok peaks.
Magicseaweed forecast for 9am: 2-3ft, cross-shore
Hatchnam wrote:
Fri Feb 23, 2018 6:44 am
Some interesting banter going on over late yesterday’s short lived but intense spike in swell. It caught everyone out.

http://www.swellnet.com/reports/forecas ... i-peaky-ne

Biggest swell ive seen hit maroubra since June 6 2016. Solid eight foot and bigger. paddled out at the north end and was lucky to make it out. It was relentless. Got pulped on the outer bank then got spat wide and made it out during a lull.

Having seen the size of the surf in the morning the only board I had packed was a 6’0.
Magicseaweed forecast for 9am: 2-3ft. Forecast for 6pm 3-5ft
Hatchnam wrote:
Wed Feb 21, 2018 7:02 pm
Punchy 3-4 foot hitting Maroubra. South to mid mostly shutting down hard on the inshore bank. North end had less punch but more shape with some runs. Watched josh ku load up a driving bottom turn then peel the top off a chunky four foot set.
Magicseaweed forecast: 3-5ft all day

These are some of Nick's recent reports (I'm assuming that, unless he says otherwise, Nick is surfing Newport):
Nick Carroll wrote:
Sat Jul 14, 2018 10:44 am
Powering today! 6-8’ and a bit messy with the earlyish high tide bit still fun. Winter’s really catching on
Magicseaweed forecast: 3-5ft all morning
Nick Carroll wrote:
Mon Jul 09, 2018 1:37 pm
Whoa, swell really booted around 11am. Boom! 10', solid, long, pretty clean though the wind shifted a bit around midday. Super fun!
Magicseaweed forecast: 4-6ft, albeit with their highest 'five star' rating. Got the wind shift timing pretty accurately
Nick Carroll wrote:
Wed Jul 04, 2018 12:14 pm
Fcuken best day of the year, hands down.

Every beach with north end sand is off the hook. And pretty much every beach has north end sand courtesy of the endless sth swells of the past three months.

result, 4-6' plus reeling lefts with a handful of people kinda hanging on the shoulder.
Magicseaweed forecast: 4-6ft
Nick Carroll wrote:
Tue Sep 04, 2018 12:56 pm
Wooo playful lil Lower Trestles this morning, mushy but fun in the 3' range

Magicseaweed forecast: 2-3ft all day

Clearly, the forecast sites aren't 100% accurate all the time and magicseaweed has seemingly undercalled quite significantly on a couple of Nick's recentish surfs and the one from February that iggy referred to. Accurate enough though? I would say so

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Re: Wave models

Post by bgreen » Thu Sep 20, 2018 5:53 am

I had the recent experience of being in South Africa and struggled to find a surf forecast that gave a reasonably accurate forecast - the forecast winds were regularly wrong so I reverted back to weather maps.

Which reminded me of a mate's old web site which now lives elsewhere: http://www.surfingvancouverisland.com/surf/predict.htm

You have to wade down past the references he lists. Point 2 is:

"From the wind strength, duration, and fetch length, one can calculate, or use a chart/table to estimate the size of the
sea's at that point, and also the period of the waves, and hence their speed, and therefore swell arrival time !.

The main problem is to get the windstrength".

This page was from 1996.

I find the surf forecasts generally undercall east swell longeivity which is a good thing. They are coarse measures which do a reasonable job at general forecasts but can be woeful for specific spots. There is also a fair bit of cut and pasting that happened at one site where the forecasts from northern NSW to Noosa was essentially the same. I also find the 7 day wind direction forecasts are often dramatically revised a day or two out.

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Re: Wave models

Post by alakaboo » Thu Sep 20, 2018 7:29 am

As they should be. 7 day wind forecasts are mostly fantasy.

I love the regional forecasts, they're so inaccurate for the places I surf it's like going back to the early 2000s.

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