A new dimension in Victorian surf forecasting

Craig Brokensha
Swellnet Analysis

Keen weather observers will have noticed new additions to the Cape du Couedic and Cape Sorell wave buoys. Each buoy was upgraded a fortnight ago.

Both buoys have had the dominant wave direction added to the graphs, however the Cape Sorell buoy is now showing data which isn't available on any other buoy around Australia: wave spectrum.

On the East Coast wave direction is crucial as swells can come from 180 degrees - north through to east and around to south. Keeping an eye on the different swell directions hitting the coast can make or break your search for waves.

Direction in the southern states isn't quite as important with most swells coming from a smaller window, that being west to south. However, knowing the direction has its benefits, as you'll soon see.

To begin with, the wave direction shown on the period graphs for Cape du Couedic and Cape Sorell (represented in graph below) is associated with the dominant swell in the water, ie if there are multiple swells in the water it isolates the swell with the most energy.

Knowing swell direction is useful when identifying strong westerly or southerly swells. For instance, a savvy Victorian surfer can calculate the travel time of a west swell hitting the Cape du Couedic wave buoy till when it hits their coast, or vice versa with a southerly swell hitting Cape Sorell and moving north towards South Australia.

In reality, this could have already be done by cross-checking the incoming swell direction with wave model forecasts, however the new data identifies shifts in the swell direction allowing a greater real time indication of the swells arrival.

The directional spread (the green bars on each graph) show the range of directions a swell is coming in from. For example, a swell may be generally coming in from a pure south-west (225 degrees) direction, but there'll also be swells coming from 235 and 215 degrees in the mix, hence the spread will be 225 +/- 10 degrees.

Pure directional groundswells will have less directional spread and a swell source that's arrived from a broader storm or conveyer belt of frontal systems will have a higher spread.

The exciting stuff is having access to the pure wave spectrum at Cape Sorell, and I'll work through it one dot point at a time:

The open ocean consists of multiple swells from a variety of directions - i.e capillary waves, wind waves, mid-range energy, and long-period groundswells

The wave spectrum is a breakdown of the sea state at the wave buoy for a period in time.

The following dot points refer to the graph below:

  • Wave energy is recorded and sampled over a 27 minute period with the most recent sample labelled on the horizontal axis, bottom right.
  • Wave frequency is shown on the top horizontal axis, with the BOM conveniently converting it to period on the bottom horizontal axis
  • Lower frequency (longer period groundswell) falls to the left hand side of the graph and higher frequency (windswell) energy to the right

The graph below is identical to the graph above but has been reproduced for the sake of clarity.

  • The Y-axis shows the energy (swell) aligned with each wave period and this is where the valuable data can be found.
  • The peaks in energy indicate the amount of swell for the corresponding period providing a quick way to see how much pure groundswell is in the ocean, if any
  • The direction for each period is shown (green), with the readings on this graph showing the groundswell is W of SW in direction
  • The lower period energy is more southerly in nature, with some very weak westerly windswell (4 seconds)
  • Arrows on the bottom axis point out the peak and average periods for the current sea state.

Making sense of this will take some time, but let's look at an example.

A singular spike of swell energy around 16 seconds with no other energy either side would indicate a pure groundswell in the 16s range, and the red Tp arrow would also hover around the 16s value.

However, if the energy spectrum is spread out and broad in nature this indicates a mix of different swells and the result will be mixed wave trains at the beach with varying size and power.

A few further points.

  • The wave spectrum will be great for identifying the amount of energy/size in the fore-runners of a new long-period groundswell .
  • If the red Tp arrow sits to the left of the peak in energy, ie around 19s, with the peak in energy sitting at 14s, this will show that the long-period forerunners have no size to them, and the bulk of swell is still mid-period energy.
  • Once the red Tp arrow lines back up with the energy spike you can concur that most of the swell is of that period.

Lastly, there is a crude way convert the energy shown on the y-axis to an approximate height in metres. Just take the square root of the spectral density.

Over the coming weeks, as better examples show up on the wave spectrum, I'll post working examples showing how to interpret it.

Cape Sorell Wave Buoy data
Cape du Couedic Wave Buoy data

Comments

DamonS's picture
DamonS's picture
DamonS commented Thursday, 29 Aug 2019 at 3:59pm

Cool. Coz the Pt Nepean buoy direction is significantly affected by tidal movements.

thermalben's picture
thermalben's picture
thermalben commented Thursday, 29 Aug 2019 at 4:12pm

Interesting... groundswell at Cape Sorell has swung from the W/SW to the S/SW in the last few hours. And there's some S/SE windswell in the mix too, under 7 seconds (though local wind readings at Cape Sorell don't have much synoptic flow).

FWIW, winds have been light to moderate W'ly at Low Rocky Point (to the south) and moderate to fresh SW at Cape Grim (to the north). Hmmm.

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno commented Thursday, 29 Aug 2019 at 4:47pm

extra information always good (WA buoys had direction at some stage?) but lets just err sweep that thumbnail pic under the rug never to be seen again...

thermalben's picture
thermalben's picture
thermalben commented Thursday, 29 Aug 2019 at 4:50pm

I suspect it’s actually a different location than the spot you’re thinking of (and yes, let’s not speak of it anymore, lest we need to rename the break Strei Sands).

caml's picture
caml's picture
caml commented Friday, 30 Aug 2019 at 12:05pm

Wa buoys do have direction VJ.

Funny how the new direction graphs are upside down from the WA graphs.
You would think they would make cdc and sorrel same but nope they have to flip it , just to make things different ?

Craig's picture
Craig's picture
Craig commented Friday, 30 Aug 2019 at 12:51pm

If it were the other way Caml the direction would interfere with the Peak Period and make it harder to read. With the current plot it looks like they've instead decided to go over the less relevant Average Period.

saltyheaven's picture
saltyheaven's picture
saltyheaven commented Thursday, 29 Aug 2019 at 9:20pm

Good stuff! Thanks for another great article.
I'm on the Tasman peninsula and don't make a habit of looking at the Sorell readings on the assumption that the bouy is too far away and not really 'upstream' from a swell point of view. This article has me wondering if I might be dismissing a useful resource...?
Care to set me straight one way or the other?

p.s. If we can arrange for a bouy somewhere down off South East Cape I know there'll be a lot of happy surfers all up and down this coast!

Craig's picture
Craig's picture
Craig commented Friday, 30 Aug 2019 at 11:08am

I believe this buoy will be of good use, especially with the added direction as if it's showing the swell really west, you could discount it, but then if more south, you'll see more size getting in.

saltyheaven's picture
saltyheaven's picture
saltyheaven commented Friday, 30 Aug 2019 at 5:52pm

Thanks for the reply Craig. I guess I'm assuming that if it's got more south in it I'll likely see it in the water here before the buoy does. Anyhow, I'll swing the buoy output into my mix for a while and see if I can draw some useful info from it. Cheers!

j-flo's picture
j-flo's picture
j-flo commented Friday, 30 Aug 2019 at 12:37pm

Thanks Craig, very helpful information. Just flagging that the Cape de Couedic link above is going to the Cape Sorell page.

Craig's picture
Craig's picture
Craig commented Friday, 30 Aug 2019 at 12:39pm

Ah, thanks, changed.

Gary G's picture
Gary G's picture
Gary G commented Friday, 30 Aug 2019 at 2:32pm

This is very exciting news for Gary, please keep these articles coming, and coming, and coming.

Young buoys are Gary’s weakness.

I’ve created a monster. Cause nobody wants to ride faceys no more, they want Gary; I’m chopped liver.

But if ya want Gary this is what I’ll give ya: a little creatine kiss from a hard licker

Vic Local's picture
Vic Local's picture
Vic Local commented Friday, 30 Aug 2019 at 3:06pm

You sick fucker Gary G. Go join the Catholic Church.

"angry online, smiley in the brine"

Gary G's picture
Gary G's picture
Gary G commented Friday, 30 Aug 2019 at 4:24pm

Gary’s more of a Kate Cebrano type o’ guy.

I’ve created a monster. Cause nobody wants to ride faceys no more, they want Gary; I’m chopped liver.

But if ya want Gary this is what I’ll give ya: a little creatine kiss from a hard licker

Lumie83's picture
Lumie83's picture
Lumie83 commented Saturday, 31 Aug 2019 at 9:18pm

Guys , is this the same tech as NSW MHL spectra’s but presented in Different format?

tango's picture
tango's picture
tango commented Saturday, 31 Aug 2019 at 11:39pm

Arrrrgghhh.

The challenge, of course, is that there are already quite a few "savvy Victorian surfers" around, Craig. Can we please join a few dots here.

Your spoon-feeding is only going to make more people more savvy. I would argue that there is ample information available on the web to predict/observe almost every facet of the ocean in close to real time if you have half an idea and there is no need to school everyone up on it. For Christs sake, it is one thing to have an intellectual discussion about the vagaries of forecasting for a particular coast around a campfire, but to have it in a public forum....?

We still get a few uncrowded surfs with sneaky swells. There's simply no need to exacerbate the crowding and put more people onto it. Seek and ye shall find. You blokes have no serious competition with forecasting so there's no need to sell out.

Love Stu's articles and have been grappling with a subscription all year, but your apparent willingness to help kill the goose laying golden eggs is a bridge too far.

thermalben's picture
thermalben's picture
thermalben commented Sunday, 1 Sep 2019 at 6:20am

"...grappling with a subscription"

C'mon mate. I grapple with my mortage repayments. Swellnet Pro subs are 30c per day.

If at this point in time - having offered subscriptions for almost six years now - you're still waiting for that something extra to get you over the line and commit your hard earned, I don't think we'll ever get there.

And I'm totally fine with that.

But please don't use one article as justification for not subscribing.

tango's picture
tango's picture
tango commented Monday, 2 Sep 2019 at 9:38am

I think you miss the point, Ben. It's not about something extra at all, and I'm not basing my view on one article by any stretch.

I'm still grappling with the same conflict that I thought I made clear over a coffee when you were down this way a while back - on one hand very much enjoying the bulk of the surfing-related content you provide and the community of interested people/knowledge the site harnesses, while on the other feeling quite sad at the impact forecasting and its evolution is having on crowds and crowding. That's what I'm grappling with - wanting to participate in and support the surf-related stuff, but wishing the forecasting would stop its relentless march towards 100% accuracy and reach so that everyone is always onto the best days and they are packed.

Like most places, we still get uncrowded days here and there, but they're much rarer, and pretty much everyone you talk to in the water or the carpark can see a clear correlation between reporting/forecasts/hype and crowds. My point is around the likely impacts arising from the promotion of access to information and upskilling more people to interpret it correctly.

I'll probably go with a subscription pretty soon, as I do appreciate the articles and discussion, and I reason that if the info is available I may as well get it too. The info you provide for forecasting can be pretty handy (though thankfully not always accurate), and while I don't really need them, the cameras are a great resource - though I'm sure there are many other people in other parts of the country who wish they'd go on the blink when the surf is good. Like I've said before, I often use forecasts as crowd predictors as much as for surf conditions. And like many people I've spoken about the issues with, I just find the evolution of reporting and forecast-related info to be a race to the bottom where the beneficiaries don't seem to be able to comprehend the impact they are having on what I consider to be the surfing experience. Our very own boiling frog.

Perhaps we can agree to disagree as we both have vested interests, though we've got common ground through both trying to make our working lives work with surfing. While you've chosen to base your livelihood around surf journalism and forecasting, I've chosen to work part-time so I can organise work around surfing as much as possible. What I do grapple with is how your entitlement to provide information in the form of forecasting and the commercial imperative you have to make your chosen source of income pay its way is also entitled to influence the lifestyle choice I (and many others, granted) have made, and even impact detrimentally on it. I've been pretty consistent on that being a source of concern.

thermalben's picture
thermalben's picture
thermalben commented Monday, 2 Sep 2019 at 9:43am

To bring it back to the current point of contention, is your beef with:

1. The software developers who wrote a program to extract spectral data from the wave buoys

2. The BoM who own and operate the buoy and provide its data free of change for the general public

3. The Australian government, who provide taxpayer funding for the buoys and other weather monitoring equipment 

4. Swellnet, who have written an explanatory article about the buoy’s new features.

Keeping in mind that any in-depth discussion about real time wave buoy data on Swellnet will be behind our paywall, so therefore only available for a tiny percentage of the surf community.

tango's picture
tango's picture
tango commented Monday, 2 Sep 2019 at 9:54am

4.

I think having an in-depth discussion behind the paywall is fine. If it were a bunch of oceanographers having a discussion in a public forum that'd be fine too. My issue lies in the often grey area where commercial activity (in this case, the disclosure of information) can impact on others' enjoyment of publicly-owned assets. No question that there are benefits, but I would prefer to see the greatest possible level of discretion built into it and an awareness of the implications of the commercial activity. While the little gains made can be viewed as little on a 1-1 basis, their cumulative impact is quite significant.

thermalben's picture
thermalben's picture
thermalben commented Monday, 2 Sep 2019 at 10:01am

Wow.. so the only reason you’re annoyed is because Swellnet is a for-profit business?

How about the same kind of discussion on one of the many surf related Facebook pages? Or how about if government-funded Surfing Australia undertake a forecasting workshop in partnership with the BOM?

tango's picture
tango's picture
tango commented Tuesday, 3 Sep 2019 at 11:33am

No, I just think that the profit motivation presents challenges for the trading off of sharing information vs the effects of providing it whether you care to acknowledge it or not. At least it's reflected a bit in some off the comments here. You love your surfing and don't want to affect it detrimentally, but as you said, you grapple with that mortgage.

As we have discussed before, your business is underpinned by natural assets which are provided "free" on public land/water. Other businesses which operates on, or provide access to, public land are subject to some form of regulation designed to consider impacts on other users and cumulative impacts - where numbers are limited and/or they pay a fee. Webcams and the provision of information/promotion of visiting public land seem to fall outside that arrangement, at least for now. As an operator of a profit-based entity in that space I think it is incumbent on Swellnet - and anyone else - to factor in the effect they have on the user experience. In my mind you guys have an effect quite similar to a self-guided tour (you promote access, offer information on the experience, suggest the best times to go, etc) though you take no responsibility for the kind of user you attract nor the numbers you attract (in line with VL's comment). Now I'm not suggesting that you are solely responsible, but you cannot deny that there are strong parallels.

For the record, I've had a chat with the bloke who runs a FB page here as well - I have no idea why he does it but he has a stack of followers (a very high % from Melbourne). He's gotten carried away from time to time and was quite receptive to considering the broader impacts. The same applies to Coastalwatch - I was in touch with them years ago when one of their early reporters was naming breaks. SA are a different animal to Swellnet. I'll take that on notice, but on the face of it you're a commercial business, they're a user group with not-for-profit status and a lot of fingers in commercial pies.

As I said in another reply below, there's a truckload of info out there. Why not just try and be more discreet and offer the tastier bits to the subscribers? You could still have a good headline which lets everyone know there's interesting and valuable material behind the wall.

Vic Local's picture
Vic Local's picture
Vic Local commented Monday, 2 Sep 2019 at 3:32pm

Ben, Tango has some very valid points here re crowds and forecasting.
My biggest beef with swellnet is long range forecasting of pumping surf. I'd say forecasting hype increases crowds by 40-50%. Not only that, it brings in the worst type of crowd. People with very little experience who can't think for themselves and get spoon fed information about waves.
I was stoked when the forecasting notes went behind the paywall. If it makes money for you that's fine with me. What I don't understand is why Swellnet puts headings on the forecaster notes that give away the key information to non-subscribers. Stuff like "Small for the rest of the week but big and clean waves due Tuesday". Any idiot reading that can then cross reference buoy readings and weather forecasts on other website. Surely a generic headline will reduce the Swellnet effect on crowds and improve your bottom line? I'm genuinely interested in why you lot have the headlines you do. It makes zero commercial sense and does the locals no favours at all.

"angry online, smiley in the brine"

Craig's picture
Craig's picture
Craig commented Monday, 2 Sep 2019 at 3:36pm

VL, I've noted this and you'll see that the titles have been more ambiguous to give more value to the subscribers. Sometimes though it's hard avoid a title without some sort of description, but it's in the back of the mind.

Scroll back and have a look.. https://www.swellnet.com/reports/australia/victoria/torquay/forecaster-n...

Vic Local's picture
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Vic Local commented Monday, 2 Sep 2019 at 3:40pm

Thanks Craig. Another site does something like "Forecast notes for 9/2 - 9/7". If you don't pay to play, the reader gets nothing. Love to see that be the standards.

"angry online, smiley in the brine"

ojackojacko's picture
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ojackojacko commented Monday, 2 Sep 2019 at 3:54pm

just a historical perspective on this. headlines evolved over the course of the 19th century to better allow newspapers to sell their product - first by summarising it, then by putting the 'peak' of the news event in it. using headlines for the forecast notes makes sense if you are trying to attract punters to read them. but if they are only for paid-up subscribers, the subscribers are going to read them anyway so no need to bring them in with a headline (the email notification or just the regularity of their publication is already enough) so Vic Local's suggestion would be sufficient to identify and chronicle the reports relative to each other. ok - apologies and i'm pissing off now

Craig's picture
Craig's picture
Craig commented Monday, 2 Sep 2019 at 3:59pm

Yes, but also we need some form of title to also entice non-subscribers to possibly sign up and read them, hence not having a nondescript version.

ojackojacko's picture
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ojackojacko commented Monday, 2 Sep 2019 at 4:08pm

fair call

Tubbabird's picture
Tubbabird's picture
Tubbabird commented Thursday, 5 Sep 2019 at 9:38am

Tango, you sound like an entitled local who doesn't like to travel. What about those of us who like to chase waves far away? We rely on forecast notes to put us in the best waves. fair enough you stroll across the street for your waves and dont like it when other people come to your spot, but those of us that aren't satisfied with mediocrity will always seek the best and latest information we can.

UTFS

tango's picture
tango's picture
tango commented Thursday, 5 Sep 2019 at 12:02pm

Nothing could be further from the truth, Tubba.

Firstly, it would be pretty rich of me to claim local status having only been in this part of the word for 15 years. I'm about as entitled as anyone can expect to be for that amount of time ie if I wait my turn and I'm in pole position then it's my turn. I have no problem with a bit of localism, and I'm happy to be on the receiving end of it if I step out of line. I understand that I live in a well-known place on many people's bucket lists and have no problem with others coming to my "spot", which is actually about 25 different reefs/beachies within a 15min drive either way. As far as I can see they are going to keep on coming.

Secondly, I quite like to travel with two trips coming up locally and o/s. I've lived in a few different places and travelled a bit surfing around the world.

I don't have the luxury of chasing waves far away, so good luck to you if you do. I reckon forecast notes would be a great resource for that, though I'm not sure why you would rely so much on them if you're a serious punter with access to all the info out there. I did quite a few missions in my youth, but you had to be able to read a weather map and understand a tide chart to do that. Your point about mediocrity sounds like a dig, but I can't see the point. I'm completely non-plussed by you seeking the latest info, so go for your life. My point is that just because you want that kind of detailed info, that isn't a great reason to publicise that kind of info and have an impact on numbers. I assume that if you were to plan a trip to coincide with a good swell etc, you'd be less than impressed if a whole bunch of other chargers like yourself were there from all over to share it with you having been spoon-fed info.

I have no trouble with the provision of the notes - they're very informative and well-written. I have a problem with the public promotion of good conditions by any party from which nobody really wins. If they stay behind the paywall with discreet headlines then I have no issue with it.

willibutler's picture
willibutler's picture
willibutler commented Sunday, 8 Sep 2019 at 10:23pm

surf hype barely matters in vicco half the people flock to bells and winki on these days with plenty of other waves along various coastlines to find and these people also then don't bother throughout the rest of the week when you can easily surf by yourself most days

ryder's picture
ryder's picture
ryder commented Sunday, 1 Sep 2019 at 8:04am

After spending a couple of weeks recently down the Victorian coast all I can say is where the bloody hell were all these ‘locals’?

goofyfoot's picture
goofyfoot's picture
goofyfoot commented Sunday, 1 Sep 2019 at 11:00am

Either in Indo or commenting furiously on Swellnet

Nick Bone's picture
Nick Bone's picture
Nick Bone commented Sunday, 1 Sep 2019 at 1:33pm

theres local Victorians all over Victoria! You didn't spot any?

I am the bone

Squidy's picture
Squidy's picture
Squidy commented Monday, 2 Sep 2019 at 8:59am

Hey Ben any chance you could do an article on swell windows for the east coast with a map outline. eg the far south swell window. Would be interesting to see where all of our swells can originate from

thermalben's picture
thermalben's picture
thermalben commented Monday, 2 Sep 2019 at 9:44am

Yep... I’ve wanted to do this for a while.. will do so over the coming months.

ojackojacko's picture
ojackojacko's picture
ojackojacko commented Monday, 2 Sep 2019 at 3:37pm

hey squidy. in great trepidation of incurring the wrath of tango for enlightening the masses ...
http://www.stormsurf.com/gc/mht/globe.html

tango's picture
tango's picture
tango commented Tuesday, 3 Sep 2019 at 11:09am

Haha, yes, yes, the spoonfeed is everywhere and Swellnet are not the only source of information. There's more than enough info out there for anyone who can read a graph and trace a line to make a half-informed call for themselves.

thermalben's picture
thermalben's picture
thermalben commented Tuesday, 15 Oct 2019 at 9:22am

This morning has a great example of how useful the new spectral data is compared to the standard Tp, Tz and Tsig values.

First glance at the Cape du Couedic wave buoy data (off Kangaroo Island) shows declining Tp from the weekend's faint long period swell. It's sitting around 12 seconds, not showing any sign of the small long period swell expected to arrive today. 

However, the spectral density shows there's a reasonable new signal at 20 seconds.

Indeed, the peak period is around 12 seconds - "peak period" being defined as the swell period associated with the peak energy spectrum (i.e. the strongest swell train) - which is leftover from yesterday. However the spectral density data allows us confirm model guidance more accurately, on swell trains that would otherwise fall under the radar.

And indeed, there are some small new lines showing on the Mid Coast this morning as this new swell fills in.

memlasurf's picture
memlasurf's picture
memlasurf commented Tuesday, 15 Oct 2019 at 2:25pm

A question Ben, I notice the swell for Victoria for one day this week is 282º which is really west, is that very common? From everything else it is mostly in the 240's which hits the MP more or less square. At 282 it is almost deflected by Cape Otway is that the case?

thermalben's picture
thermalben's picture
thermalben commented Tuesday, 15 Oct 2019 at 2:32pm

Actually 282 degrees is W/NW.

The key is in the swell period (very low) which means it's short range windswell from the pre-frontal NW thru' W/NW airstream. So, it's not a major surf producer for this region.

The North Coast of Tasmania on the other hand...

memlasurf's picture
memlasurf's picture
memlasurf commented Tuesday, 15 Oct 2019 at 2:35pm

Ha, ha yes I thought about that part of Tassie always a beautiful part of the world particularly on a sunny day and if they had swell there are heaps of potential setups. Do get surf I am told by a few in the know over there.

velocityjohnno's picture
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velocityjohnno commented Tuesday, 15 Oct 2019 at 4:42pm

:)