Tasman Lows don't produce 'groundswells' for South Coast NSW

OldSouth's picture
OldSouth started the topic in Monday, 9 Oct 2017 at 9:27am

Tasman lows don't produce 'groundswells for the south coast of nsw . A 1.6m plus swell with a period of 8, 10 or even 12 sec is not a groundswell. It is crap. They look nice from the south due to smoother bathymetric transition close to shore but it's always the same, everyone running around all day looking for a spot which isn't closing out or snipping off. Also for high quality waves what is required is clean energy, This means NO other wave energy or artefacts on or in the water. So it's actually bad to have a number of swells acting. When we have a clean swell from say the Ross Sea any little bit of other swell eg East windswell will ruin it or drastically reduce the wave quality. Sometimes we see on here that there is a groundswell forecast but even better we have another 2 swell sources present. That's nonsense boys. Chances are that if the system producing swell is directly influencing our atmospheric weather then it's local and can't produce decent surf. We don't get groundswell from the bass straight nor the south tip of New Zealand . There's another reference to groundswell in the comment above, a 3m groundswell in Sydney. At that amplitude it would have to have a Hugh period well above 20 sec and taking into account shoaling and refraction it could produce waves over 8m high. I saw barrels near my place in 1992 in a swell like that which were about 8 m high with about 2 m thick lip throttling way out square. We very rarely get a 3m groundswell on the east coast. I've only seen a few and I've seen em all.

thermalben's picture
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thermalben commented Monday, 9 Oct 2017 at 9:27am

"Tasman lows don't produce groundswells for South Coast of NSW"... eh? 

Almost everything you've written is incorrect in some way shape or form - where your evidence, other than "I've seen em all"?

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OldSouth commented Monday, 9 Oct 2017 at 9:27am

Hahaha ,Ben that was a rather empty reply given your disagreement with everything I stated and your emphasis on evidence. Groove I'm sorry to hear about the crowd problem your having up there , it seems that they may have had advice to head there for the better south swell reception such as the advice on swellnet for example. The only hope is that people get the shits coz it's not what they were expecting and give up blowing in.

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thermalben commented Monday, 9 Oct 2017 at 9:28am

OS, I've been writing comprehensive surf forecasts on Swellnet for more than fifteen years now, in which I detail the precise origins of each swell, and estimated its characteristics once it makes landfall.

Whilst I occasionally get it wrong from time to time - of which I'm always the first to point it out, and then discuss the reasons why the forecast was incorrect - I've never had anyone pull me up and accuse me of publishing false information (i.e. "You said that south swell originated from eastern Bass Strait, that's not true - it came from here instead). All of my evidence is there for you in the Forecaster Notes archives. 

However, if you're going to make wild claims (as per your earlier post), you need to back it up with your own evidence. 

Even better - if you see me incorrectly analyse a swell event in the future, why don't you point it out at the time? Then we can discuss it with the benefit of having real time buoy data and weather charts to verify the facts.

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OldSouth commented Monday, 9 Oct 2017 at 9:28am

Surely it's not such a wild claim to suggest that a gale exiting the bass straight won't produce groundswell for the South Coast. It could depend on what our opinion is over what is a groundswell. It's my opinion that the term is very loosely and overly used by Swellnet. You can give me a whole bunch of published evidence about the definitions and the nature of wave energy generation and transmission, and the chances are that I've seen it, but my experience in pioneering the east coasts most exposed and heavy waves for 40 + years paints a very clear picture . If the bouy says 1.5 meters at 10 sec that's hardly a groundswell and certainly miles from a strong or solid groundswell. I doubt that I'm the only person amongst experienced surfers with this opinion. It's absolutely no secret about the collapse and softening of the old surf culture and the rise of the new hype driven industry and it is quite aggressive at shunning any opinion from the old school. Thanks for your invite to put my opinion up in future and from time to time I certainly will. Perhaps we can see some of your data for this Tasman low which is finishing up just now, and also regarding any polar low activity over the last five days too ,thanks.

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thermalben commented Monday, 9 Oct 2017 at 9:29am

(note: the initial comments above were pulled from a Sydney Forecaster Notes discussion; they're better off in our forums)

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thermalben commented Monday, 9 Oct 2017 at 9:33am

Re: "It could depend on what our opinion is over what is a groundswell. It's my opinion that the term is very loosely and overly used by Swellnet."

I alternate between the terms 'windswell' and 'groundswell' depending on the characteristics of the swell, rather than its period. Sometimes I'll include 'long period', 'long range', 'short range', 'mid-range' but that's usually just to qualify or distinguish it against other swells in the same forecast period.

Windswells are weaker swells, usually quite peaky and random, and short lived, best suited to beachbreaks. Groundswells are long lined, well defined, well suited to reefs and points (obviously, dependent on direction).

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udo commented Monday, 9 Oct 2017 at 9:37am

8mt swell with 2mt thick lips in 1992

What month in 1992 ?

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heals commented Monday, 9 Oct 2017 at 10:40am

@oldsouth,
It seems like you're mixing up general statements with specific examples - which I assume refer to your local spot (in 1992 do you really think everywhere had two meter lips? Of course not, that's just your limited observation). However, I can assure you that my local won't close out or "snip off" in a 12 second 1.6 meter south swell. As long as local winds co-operated it'd It'd be four feet and off the richter.

Also, the next town north there's a beachbreak that responds well to a mix of swells in the water, it creates peaks from headland to headland, and from what I know Sydney's northern beaches likes an east swell overlaying a south swell, because without it the south swell would just close out. So all that is in direct contradiction to what you're saying.

Plus, to say that we don't get groundswells from the tip of NZ South Island is absurdly incorrect and I've no idea how you could justify it? They're rare but they happen, and almost by virtue of distance alone they arrive as groundswells. I'm curious about your definition.

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OldSouth commented Monday, 9 Oct 2017 at 5:08pm

G'day udo , pretty sure it was some time after easter, still warm. It wasn't an 8m swell but probably nearer to 3m sse. It must have come from a long way past south NZ and yes it definitely wasn't like that everywhere. There was tons of refraction and the sea floor profile is VERY steep so it seemed that all of the energy from hundreds of metres either side of the impact point was focused in. Perfect left right peak and the heaviest wave I've seen I'm my life. But I mention it as a comment on how serious a genuine long range 3m grounds really is , what the ramifications are, and how easy it is to over call the size of good groundswell.

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thermalben commented Monday, 9 Oct 2017 at 1:39pm

MHL's network of wave buoys record 3m southerly groundswells every other week. They are a very common occurence in NSW. 

And, if a swell came from "a long way past south NZ", then it'd be a S/SE or even SE swell, not S'ly.

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OldSouth commented Monday, 9 Oct 2017 at 5:51pm

Yes Ben , a sse or s/se swell just as I have written in my response to Udo's post. Did I write south, sorry I can't see it there.

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thermalben commented Monday, 9 Oct 2017 at 7:20pm

Did you edit your post? Has a time stamp of 5:08pm yet my comment after it was several hours earlier.

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thermalben commented Monday, 9 Oct 2017 at 7:59pm

Anyway, how would you classify today's swell?

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OldSouth commented Monday, 9 Oct 2017 at 8:24pm

Yeh I edited (...it's easy to over all the size of a good...) to ( ....it's easy to over call the size of a good...). It just didn't make sense at all , geezus bad timing, you'd have a record of the edit I hope. Nuh the sse is how it was. Anyway semantics, and a diversion from the point.

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OldSouth commented Monday, 9 Oct 2017 at 9:20pm

Really good swell today for sure. About as good as a windswell gets round here. When the wind swung and groomed it a bit it was real good. Not so good reefs and points due to the short period but good beach. I saw those shots of Cronulla point and Shark Island , where I surfed a lot as a kid, and it looked pretty bloody good , nice bit of groundy there but still close spaced.I reckon that here the swell situation was pretty much as your wave forecast model called it, about 1.5m at about 10sec, I think the period might've been a bit bigger even. Nice windswell. No Se groundswell for the South Coast off that local system.

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thermalben commented Tuesday, 10 Oct 2017 at 7:04am

What's your reasoning for calling it a windswell?

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Craig commented Tuesday, 10 Oct 2017 at 7:54am

OldSouth, swell hit 13s yesterday out of the SE, mixed in with some weaker mid-period S energy.

Surfing, the SE groundswell swell was inconsistent as expected, with it being generated off New Zealand's South Island but there were great defined groundswell lines hitting the reef and shelf I surfed all morning.

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OldSouth commented Tuesday, 10 Oct 2017 at 10:53am

Ben it was a windswell here for all the reasons I've stated previously , the period was wasn't high enough to call simply because it was off a local weather system , but more importantly the way it was hitting down here. Not enough to excite my favourite bommies and headlands which are excellent barometers for the state of the swell. Plenty of slab snapshots for your mates but as I said , some good beach breaks. So done and dusted , windswell.

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thermalben commented Tuesday, 10 Oct 2017 at 11:53am

Yesterday's swell wasn't "off a local weather system", it originated from a low off the SW tip of New Zealand's South Island. 

That's a travel distance of approx 1,600km to the South Coast, 1,800km to Sydney, 1,900km to the Mid North Coast and 2,100km to the Gold Coast. 

What is your cut-off distance for a 'windswell' to become a 'groundswell'?

And at what swell periods does a 'windswell' become a 'groundswell'?

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slabfinder commented Tuesday, 10 Oct 2017 at 3:59pm

I'd agree with OldSouth, yesterday's swell wasn't a groundswell on the south coast. I tend to think anything with a period of less than 14-15 secs as not a groundswell, just swell and if the period is less than about 10 then it's just windswell(yes, I know all swell comes from wind). Under 6 it's nothing more than windwaves(chop in other words).

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thermalben commented Tuesday, 10 Oct 2017 at 4:20pm

Classifying a swell on period alone is fraught with difficulty.

Compare a 3m swell at 10 seconds to a 0.5m swell at 16 seconds. 

Even a solid trade swell at 8 seconds is gonna kick your arse, if you're in the right (wrong) spot at the right  (wrong) time.

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stan1972 commented Tuesday, 10 Oct 2017 at 4:27pm

There's no textbook consensus as to where windswell stops and groundswell begins but most agencies/companies put it between 10 seconds and 14 seconds - and in australia we tend to err toward the lower end. it's kind of pointless to specify the period exactly as a windswell doesn't instantly transform when it reaches a certain period, so a range makes more sense.

In Sydney we see many 10 second swells that meet groundswell consideration. i would've thought the south coast would be the same, however you're also talking about origin and I haven't read all the comments.

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OldSouth commented Tuesday, 10 Oct 2017 at 4:43pm

Tasman lows are definitely local systems just as surely as The Tasman sea is our local . Even the furthest corner , the sw tip of NZ is only 1600kms from here as you stated, that's way too short for groundswell generation as was seen with yesterday's Se windswell on the South Coast. That's clearly about the furthest distance a low can be in the Tasman hence as I wrote in my post, Tasman lows don't produce groundswells for the South Coast. Thousands of ks of travel is needed even for small groundswell generation so the north coast and southern Qld can get good groundy with these lows. I reckon Slabfinder knows what he's talking about , that groundswell starts at around 14-15secs for smaller swell. Much higher for larger swells, once again, a 3m groundswell is a monster with a huge period well above 20sec and capable of waves like I described. Those swells being made way down in the Southern ocean are good and when they swing in from many thousands of ks away, past NZ they are great. These are the swells which swellnet has tons of trouble resolving . I know there are many variables determining the nature of swell, such as the size , intensity , shape and duration of lows and their fetches. But 1600kms is far short no matter.

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OldSouth commented Tuesday, 10 Oct 2017 at 4:49pm

Craig, yep I thought the swell yesterday was a bit longer than 10 sec but It makes little difference when we're talking about groundy. And please, please don't tell me you were surfing in Sydney or anywhere outside the range of my post.

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OldSouth commented Tuesday, 10 Oct 2017 at 5:06pm

Heals it's good that you have waves nearby which work in wind swells and multi swell setup, that's exactly what we want when the swell is crap. But nothing you have said is in any way contradictory to what I said. Please read my post again and you will see that I did not say that every where had 2m thick lips. In fact that is contradictory to what I said, which is that that one wave at that one spot for about 6_8 secs had that lip. And I just know that no where on the whole east Coast of Aus would be capable of such a feat. I have written an basic explanation as to why I don't call any swell from the sw tip of NZ a groundy down here.

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thermalben commented Tuesday, 10 Oct 2017 at 5:14pm

A fetch length of 1600km is windswell material?

I grew up surfing in SA on the metro beaches, where the fetch length was 50km across the gulf. THAT is a windswell source.

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heals commented Tuesday, 10 Oct 2017 at 5:23pm

It's not me that's contradicting myself.

"it's good that you have waves nearby which work in wind swells and multi swell setup, that's exactly what we want"
vs.
" So it's actually bad to have a number of swells acting."

and

" I saw barrels near my place in 1992 in a swell like that which were about 8 m high with about 2 m thick lip throttling way out square." (note the plural - "barrels")
vs.
"one wave at that one spot for about 6_8 secs had that lip"

You're either bad at expressing yourself or you're just looking for an argument.

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thermalben commented Tuesday, 10 Oct 2017 at 5:25pm

Look OldSouth, if you want to describe any surf with periods of 14 seconds or less as windswells, that's fine with me. We'll have to agree to disagree.

But so many of your other points just don't make sense, or are your personal interepretation. And that's fine - but is there any merit in debating 'em? For example:

"Tasman lows don't produce 'groundswells for the south coast of nsw" - I disagree.

"A 1.6m plus swell with a period of 8, 10 or even 12 sec is not a groundswell. It is crap." - I disagree.

"They look nice from the south due to smoother bathymetric transition close to shore but it's always the same, everyone running around all day looking for a spot which isn't closing out or snipping off." - some coasts yes, plenty of coasts not at all.

"Also for high quality waves what is required is clean energy, This means NO other wave energy or artefacts on or in the water. So it's actually bad to have a number of swells acting." - I disagree. If you're surfing beachbreaks, additional swell trains contribute to great waves.

"When we have a clean swell from say the Ross Sea any little bit of other swell eg East windswell will ruin it or drastically reduce the wave quality." - I disagree.

"Sometimes we see on here that there is a groundswell forecast but even better we have another 2 swell sources present. That's nonsense boys." - I disagree.

"Chances are that if the system producing swell is directly influencing our atmospheric weather then it's local and can't produce decent surf." - I disagree. Monday's swell was generated by a system that didn't influence our weather - it was near New Zealand. But you still called it local.

"We don't get groundswell from the bass straight nor the south tip of New Zealand." - I disagree. We receive groundswells from both sources.

"...a 3m groundswell in Sydney. At that amplitude it would have to have a Hugh period well above 20 sec and taking into account shoaling and refraction it could produce waves over 8m high." - I disagree. 3m swells can exhibit a wide range of periods, depending on the source.

"We very rarely get a 3m groundswell on the east coast. I've only seen a few and I've seen em all." - I disagree. we get 3m groundswells frequently on the East Coast.

etc etc.

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batfink commented Tuesday, 10 Oct 2017 at 5:46pm

Can't agree with your definition of ground swell old south, and I don't know any surfer that would be so specific about the conditions that would have to be met for it to be called groundswell, that involve a particular slab with a 2m thick lip.

Ultimately it makes most sense if judged on the swell having real lines, not just peaks here and there, come in real sets of 3, 4, 5 or more waves, with real and often regular breaks in between, just like windswells don't do. Sure there is a margin in between for loose interpretation, but anything from south of new zealand to hit here, south or north coast, will have travelled far enough to be considered ground swell by the time it gets here.

The existence of another swell in the water, which is common, is neither here nor there, nor the conditions of the local weather at the time. Your definition is unusually tight.

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happyasS commented Tuesday, 10 Oct 2017 at 10:01pm

the notable thing about south coast NSW is its generally very favourable wind conditions year round, and consistent (albeit smaller period) swell. plenty of very good surf down there, even at 12 seconds. can it match margs, no, but who cares.

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OldSouth commented Wednesday, 11 Oct 2017 at 8:27am

Heals your reply is impertinent. , has nothing to do with the topic. You have unfortunately not even quoted me properly where i mentioned that a break with waves in multiple swell is ok when the (swell is crap). I don't much fancy paddling frantically around for a few pissweak peaks. It's an age old problem for surfers when the swell is confused.
The one about the use of plural , it seems u missed the point of the comment all together ,which is the nature of groundswell and highlighting the flamboyant sloppy use of the terms on this site leading to unnecessary frenzy. As for me being bad at expressing myself ,hahaha, maybe ,but it seems perhaps no worse than you .

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thermalben commented Wednesday, 11 Oct 2017 at 8:56am

How is the 'flamboyant, sloppy' use of the word 'groundswell' in my Forecaster Notes 'leading to unnecessary frenzy'?

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Gaz1799 commented Wednesday, 11 Oct 2017 at 9:41am

@Ben I grew up in the same area as you and the difference between a decent wind/ground swell is pretty stark for us, especially when comparing the mid/south coast.
A raging 35 knot onshore can throw up 3-4 foot metro surf in the right places here but if the wind backs to 20 knots or less then may as well go home. If the wind swings much off dead west then the swell ceases pretty fast. Groundswell only enters the mid on a WSWish swell. I'm no forecaster but I've always considered a wind-swell to be fairly local as a result.

I've always assumed that if the weather within 100 km is pretty good with no lows etc isobars not close either then any swell, regardless of size has to be groundswell based on the time/distance it would have had to travel alone. Does that sound right? Is long range windswell even a thing?

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Craig commented Wednesday, 11 Oct 2017 at 9:46am

On that last sentence, that's what I identify as mid-period energy. That long-range windswell sorts itself and grows in period a little to a maximum (all dependent on the wind strengths reached).

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thermalben commented Wednesday, 11 Oct 2017 at 10:13am

Gaz, "long range windswell" is a bit of an oxymoron.

Windswells by nature are swells generated by local fetches. As soon as swell energy moves away from the source, it starts to decay - and becase windswells have low periods, they rapidly fade in size to the point where they're no longer useful from a surfing perspective.

Obviously, the transition point between windswells and groundswells needs to be flexible. From my perspective, it's more about the physical characteristics of the swell - the way it looks, the way it feels - rather than an arbitray classification based on swell period or source distance to destination. 

Probably the most important point in this discussion is that different coasts have different preferred swell periods/sources (as well as size/direction characteristics). Regions with lots of beachbreaks prefer lower periods source closer to the mainland, regions with finely tuned reefbreaks prefer longer periods source much further away. And there's a wide range of combinations in the middle of this too.

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Spuddups commented Wednesday, 11 Oct 2017 at 10:55am

OldSouth, for what it's worth I reckon you need a bit of a re-think on your groundswell theory.

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Gaz1799 commented Wednesday, 11 Oct 2017 at 11:04am

Agreed on long range windswell oxymoron, I noticed the 1600 km windswell comment and didn't agree at all.

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thermalben commented Wednesday, 11 Oct 2017 at 11:10am

Monday's energy travelled ~2,000km up here to Far Northern NSW; the groundswell corduroy was divine. 

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lostdoggy commented Wednesday, 11 Oct 2017 at 1:58pm

There was some good size and power at the magnets too. Wished I'd packed the step up.

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freeride76 commented Wednesday, 11 Oct 2017 at 2:31pm

"Is long range windswell even a thing?"

Sure it is. They're called tradewind swells and for a lot of places it's staple surf.

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thermalben commented Wednesday, 11 Oct 2017 at 2:35pm

I'd argue that tradeswell is neither windswell nor groundswell.

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freeride76 commented Wednesday, 11 Oct 2017 at 2:42pm

Sure, you can put it into a separate category if you like but the period signature and nature of the source fetch would seem to put it much more in the windswell than groundswell camp.

Not saying it impacts the surf quality though.

For this region, swell direction and local bathymetry are far more important factors than swell period.

I always have a chuckle when I overhear backpackers talking in the surf about how Magic Seaweed has forecast a period increase and they are getting all frothy over it. Mostly, with rare exceptions, it means jackshitt around here.

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thermalben commented Wednesday, 11 Oct 2017 at 3:12pm

There are also different categories of tradeswells, with the resulting surf dependent on fetch alignment, fetch length, wind strength, distance from head-of-fetch to mainland etc.. 

This discussion has prompted me to start building a glossary of sorts, where we can reference (and debate) them all in one location.

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freeride76 commented Wednesday, 11 Oct 2017 at 3:18pm

I think you're splitting hairs trying to create different categories of tradeswells.

Tradeswells are a category and I think most SEQLD/NENSW surfers know one when they see one and when they surf one. They are all formed by the same broad synoptic pattern and have very similar characteristics.
Sure they ain't all alike but there's more similarity between the worst and the best tradeswell than between a directional S'ly groundswell and a tradeswell.

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thermalben commented Wednesday, 11 Oct 2017 at 3:33pm

I'm just pointing out that in the same way each groundswell has a different characteristic, so to do tradeswells. A super-charged trade swell from a fully developed sea state - even if wind speeds are under 35kts - behaves much more like a groundswell (in the surf zone) than a windswell, in my opinion.

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OldSouth commented Thursday, 25 Jan 2018 at 8:20am

Just saw this again. Where you describe a 50km fetch in ur bay, and you say 'That's' a windswell source. Im sure that 'That' is not a windswell source. Its a source of chop and whitecaps. Seriously dude over that short distance was, or is ,there any equipment which could resolve any pattern at all from the mess. There would be no period, no wave height just a randomly occurring maximum.

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Craig commented Thursday, 25 Jan 2018 at 8:29am

OldSouth, last week, very strong Tasman low generating 14-15 second groundswell to the northern NSW coast. Swell was too straight for most beaches and only lit up the reefs and points.

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OldSouth commented Thursday, 25 Jan 2018 at 9:45am

Hey thats great Craig, sometimes I wish I was all the way up there but I know how crowded its getting now. Im all about the south mate. Completely different.

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Craig commented Thursday, 25 Jan 2018 at 9:53am

It was groundswell in the south as well, more around 13s though.

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OldSouth commented Thursday, 25 Jan 2018 at 10:48am

Hahaha . Really that was a pretty shit system for us. The psudo professionals didn't like it either and all they need is a snapshot under a heavy lip. Groundswell at 13 secs, no.