ECL?

[2nd Reef]

Yoo hoo Longinus!

I ain't gonna let you forget this one...

Its still longish range but this season looks like it could be the biggest ever for the Comp at Teahupoo. My buoy for Tahiti is calling 12 feet by next Friday and rising! Serious question - would they run the comp as a tow in event or move it?

You've got about 8 hours to divine 12 feet of swell.

[thermalben]

Cmon Nick, no one would have complained if forecasters hadnt called it in the first place. It's a big call to go straight to "biggest swell in 30 years" and put it in the Sydney Morning Herald.

Which forecasters called it the biggest swell in 30 years?

[LONGINUS]

Yoo hoo Longinus!

I ain't gonna let you forget this one...

Its still longish range but this season looks like it could be the biggest ever for the Comp at Teahupoo. My buoy for Tahiti is calling 12 feet by next Friday and rising! Serious question - would they run the comp as a tow in event or move it?

You've got about 8 hours to divine 12 feet of swell.

Cape and chicken bones at the ready

[LONGINUS]

Cmon Nick, no one would have complained if forecasters hadnt called it in the first place. It's a big call to go straight to "biggest swell in 30 years" and put it in the Sydney Morning Herald.

Which forecasters called it the biggest swell in 30 years?

BAM
http://www.smh.com.au/news/national/big ... 63293.html

[LONGINUS]

Hey 2nd, Alex should be in line for some of this Vicco action and damn he knows the spots. Tried to convince him to come with me to the Mentawais

[thermalben]

Cmon Nick, no one would have complained if forecasters hadnt called it in the first place. It's a big call to go straight to "biggest swell in 30 years" and put it in the Sydney Morning Herald.

Which forecasters called it the biggest swell in 30 years?

BAM
http://www.smh.com.au/news/national/big ... 63293.html

The only forecaster mentioned in that article was Rob Webb from the BOM, of which he said that "surf conditions would be dangerous, particularly on south-facing beaches". He didn't mention anything about it being the biggest swell in 30 years.

[LONGINUS]

Yoo hoo Longinus!

I ain't gonna let you forget this one...

Its still longish range but this season looks like it could be the biggest ever for the Comp at Teahupoo. My buoy for Tahiti is calling 12 feet by next Friday and rising! Serious question - would they run the comp as a tow in event or move it?

You've got about 8 hours to divine 12 feet of swell.

http://www.surfingatlas.com/spot/33 My buoy is stuck at 8 feet - heavily influenced by the 25 knots of onshore wind I expect - SNIP SNAP!

[LONGINUS]

The only forecaster mentioned in that article was Rob Webb from the BOM, of which he said that "surf conditions would be dangerous, particularly on south-facing beaches". He didn't mention anything about it being the biggest swell in 30 years.

Um, the title of the article is...Biggest Swell in 30 years... guess thats where I um...got it from Are you seeing the full article Ben?

[thermalben]

Yes, I see the full article. But it wasn't written by a forecaster - that's all.

[nosedrip]

Cmon Nick, no one would have complained if forecasters hadnt called it in the first place. It's a big call to go straight to "biggest swell in 30 years" and put it in the Sydney Morning Herald.

Which forecasters called it the biggest swell in 30 years?

BAM
http://www.smh.com.au/news/national/big ... 63293.html

The only forecaster mentioned in that article was Rob Webb from the BOM, of which he said that "surf conditions would be dangerous, particularly on south-facing beaches". He didn't mention anything about it being the biggest swell in 30 years.

Um, the title of the article is...Biggest Swell in 30 years... guess thats where I um...got it from Are you seeing the full article Ben?

Not sure if I'm missing something or maybe I'm just drunk - but the article you've linked to is dated April 9, 2006....it's an archived article.

[steve shearer]

Near direct Southerly swells are always severely attenuated by the bottom topography of sea mounts and sub sea mounts off NSW that go all the way to the 100 m contour. The Coastalwatch SWAN model takes good consideration of most of those factors

I highly doubt there's a wave model with algorithms that take into account the different effects of swell direction and period, and the way that is attenuated, refracted or shaped by bathymetry on such a micro scale: but if you have evidence to the contrary then out with it.

[LONGINUS]

Steve,

Theres nothing in public domain to my knowledge but the NOAA Wave Watch III model that virtually all automatad buoy data draws from is only the unclassified version of what the US Navy uses. I spent a lot of time operating on submarines out of Hawaii based in Pearl and the models we had access to for planning purposes were insane. As you know, as surfers we are really only concerned with what is happening in the top 10 metres of the water column and WW3 addresses that on a global scale. For my site we needed buoy data to cover all of our 4000 surf spots so we came up with our own algorithm that draws directly from WW3 GRIB data. It's difficult to turn what is essentially an open water forecasting tool into something that is accurate nearshore but if you want one algorithm to cover the entire world then you have to accept some limitations.

The truth is that the final size and period of a breaking wave is the product of what is happening in up to 1000m of water column. Iv'e been at 200M in large storms and still felt the sub corkscrewing through the water. Off Hawaii where open ocean swells are ramping up from the 1000m to the 100m contour extremely quickly the effect is enormous. Once at 100M we lost 30M in depth in a fraction of a second. I can only describe it as a feeling of underwater turbulence, similar to when a plane drops without warning. What it was was an 'internal wave' within the water column. So if your in 150M of water at 100M and suddenly you loose 30M in depth while you are doing 15 knots and the bottom is lava or basalt...the holes in the swiss cheese start to line up pretty quickly. Anyway so thats why the USN put a lot of work into region specific models that account for every effect down to 1000M in depth, its like crunching an entire global model just for the Hawaiian Islands. When we came in after the internal wave incident I went up to forecasting and the guy there said - "how'd that internal wave treat ya off Hilo?" I asked him how he knew and he lent out and patted an enormous grey box that was basically a stripped down CRAY supercomputer with an Atari sticker on it as a joke and he said "she told me" He had actually forecast it with the model.

Side benefit was that this model was the most accurate surf forecasting tool for Hawaii you could ever imagine. I took great pleasure in using US tax payers funds by printing out forecasts before I decided where to go for surf and it was accurate to the inch. An interesting feature was that you could reverse model the size of the surf you were after to see what weather pattern would create it. Like all good US military planning tools it would have a 'bodycount' on the bottom of the screen to show you how severe the storm damage would be to create the surf you were after. I modelled 30, 50, 100 and even 1000 year storm events on the North Shore. The 1000 year storm event created 60 foot waves at Pipeline and forecasted 120 feet waves cresting at Waimea before 'breaking down' due to surface tension. Unfortunately in that model, most of the population of Haleiwa didnt make it. :?

Anyway, there are a lot of good forecasters on this site, you included but my point is that from experience, with larges storm events in the Tasman, often the total bathymetry can put a very substantial wobble into the final size of nearshore waves in NSW, particularly in swells with a strong southerly vector. These swells have to navigate around and between a very complex connection of sub surface features that stretch all the way from the Lord Howe Rise to Eastern Victoria and to my knowledge there is no known model that takes due account of all of this for the Australian station , you just have to apply it's effect as a fudge factor based on experience.

[puurri]

[SAsurfa]

Interesting post Longinus, did you manage to get the algorithm used at all or explore any of the maths behind it??

It's an interesting topic trying to find a broad formula to convert model data into near shore wave heights and I don't think we'll ever come up with just one simple answer. It would be more like a tweaked version for each different location or area depending on its unique bathymetric and quirky characteristics.

[oldman]

More value in hindcasting it every time I think, you can find out heaps about how fetches affect different bits of coast etc.

Fcukin amen.

Anyone who is interested in forecasting should be doing plenty of hindcasting, the only way to really learn.

Longinus that is fair dinkum interesting stuff, and I take your point about the ocean topography between here and NZ have various peaks and troughs etc that would have an effect on the wave heights at the coast.

I think you getting a bit technical if you are looking for reasons why the biggest swell event in 30 years didn't happen. It could have been all those intricate little things, but it was more likely to be that the forecast swells were derived from forecast weather, and both the forecasts and the weather changed.

I've got little doubt that if the earlier models came to pass that we would have seen the biggest swell for many a year.

So we got a fraction of the energy that was earlier forecast. And still it worked out to 3 and a bit days of bumper offshore swell!

I don't mind you having a go at anyone getting a bit hyped, BTW. I'm with 2nd reef and others though, forecasting is half the fun!

[Nick Carroll]

Well I reckon if you believed the surface chart progs 10 days out, you had a damn good chance at the biggest SE groundswell in many years. Up till about 5 days out, the combined charts were suggesting a 1000 nm fetch of what'd likely have been 50 knot winds over two days aimed straight at the central NSW coast from just under and to the west of the NZ south island.

As it turned out, the forecasts were tripping a bit and the scenario played out a lot weaker. But the same swell angle and the fetch in a similar spot -- a lot shorter and a fair bit less wind -- hit Sydney etc on Wednesday with a solid 6-8' of excellent groundswell, with no local weather interference.

Imagine that swell, tripled in intensity. Would that have been enough for everyone? Hell what showed up was too much for a large majority.

longinus you have a point but you ain't taking it anywhere. Here's a interesting thing that happens on long period sse groundswells along the central NSW coast, and that we saw happen this past week: the swell actually is refracted by the continental shelf, coming in and striking from a more easterly angle than might be expected. You don't see this happening on shorter interval southerly-change type swells -- which always look a lot more southerly -- because the period isn't sufficient for the swells to be grounding on the shelf.

[Grooter]

I don't really know what it was all about but Longinus that was a great post from a layman's perspective

[LONGINUS]

longinus you have a point but you ain't taking it anywhere. Here's a interesting thing that happens on long period sse groundswells along the central NSW coast, and that we saw happen this past week: the swell actually is refracted by the continental shelf, coming in and striking from a more easterly angle than might be expected. You don't see this happening on shorter interval southerly-change type swells -- which always look a lot more southerly -- because the period isn't sufficient for the swells to be grounding on the shelf.

Yep, that refraction on the 140M contour (pretty much the universal continental shelf definition) shows you that there is a lot happening in the entire water column. In fact on older continents such as Australia and Continental USA you have a much larger presence of submarine canyons that fracture along your shelf. In comparision to Hawaii's shelf which is far more recent. The shelf is basically what was exposed during the last glaciation period and ancient rivers, earthquakes etc shaped the topography. There are several places on the NSW coast where those fractures effectively funnel long period ground swell right onto the break and it will be significantly larger here than elsewhere. It's the same as the Hawaii effect, the ramp up from deep water to shelf is enhanced by channeling the energy in a deep canyon. the best example of this anywhere is the Monterey Submarine Canyon that funnels and channels deep ground swell straight onto Mavericks.

It's just so difficult to plug things like that into a model and have it be accurate globally but on a regional basis, if you design a model that accounts for it locally it's super accurate. Just too expensive to design a model for each area. Your observation of the refraction is spot on but we can only really apply it as an 'experience' or 'fudge' factor because we don't have a model that can incorporate it.