Recently, Swellnet forecast a swell to hit Tahiti from near enough two weeks out - the waves coming in very close to the original prediction.
This is possible for coastlines facing into large ocean basins where both the movement of storms is repetitious and swell travel adds up to a long lead time.
Also, when the swells hit they usually do so in what might be considered a classical manner: a steep rise, rounding to a peak, then a long tail, the whole process sometimes lasting many days.
This predictable, extended process contrasts sharply with the experience of forecasting on Australia's East Coast, particularly the lower NSW coastline. The swell that struck on the weekend being a great example.
The MHL Sydney Wave Buoy trace from the last three days provides a great insight into the mercurial aspect of East Coast swells, and why they can be tricky to forecast.
The swell was predicted to jump fast late on Saturday, which it did, however the wave buoy shows an interesting signature from mid-Saturday to mid-Sunday. The recorded wave heights showing two steep increases in size - see image below left.
MHL Sydney Wave Buoy observations (Significant and Maximum Wave Height), and the swell producing low
Known in forecasting speak as J-curves they indicate a rapid jump in size associated with the arrival of strong swell front. In this case, there are two J-curves, one after the other. The sharp upticks in size tells us that the low deepened significantly. Which it did, doubling in strength during the weekend compared to Friday's forecast.
Unlike Tahiti, where the swell is produced many thousand kilometres away, and hence any changes can be logged in advance, East Coast systems deepen right on our doorstep. For Sydney, the swell was produced approximately 500 kms away, the South Coast even closer, making for a very dynamic forecast window.
What's also impressive - if only from a forecaster's point of view, surfers wouldn't be thrilled - is the sharp decline in size seen through yesterday. Measured by either 'significant' wave height or 'max' wave height, the recorded wave heights halved from midnight Sunday to midnight Monday.
The steep decline was due to the swell source being rapidly cut off. As the swell-producing low tracked southwest towards Tasmania, the southerly fetch was cut off by Green Cape and the jutting southeast corner of NSW - see image above right.
Though it shut down the swell, the southwest-tracking low created offshore wind for most of the NSW coastline. Thus, surfers in NSW awoke on Monday to huge waves and groomed conditions, at northern ends at least. However, it was case of 'blink and you'll miss it' with the swell noticeably dropping throughout the day. From serious paddle guns in the morning to grovellers in the late afternoon.
All images were taken yesterday morning.
Matt Davies (above and below in sequence) getting slung in from behind the rocks
Comments
Truly blessed and humbled by our Wave God's Majesty...
All hail Craig...the new messiah!
Blink and you'll miss it raises the bar in next level Tributes to Huey!
Salute #1 swellnet!
Crazy the size drop off on Monday. Easy 10 foot out of control death slabs in the morning, down to beautiful 4 foot glass in the arvo at the same spot.
Yeah Epic 2 day swell, best south swell (for my local anyways) for possibly 3 years in terms of wind, angle and period. Not to mention perfect tide in morning and afternoon. Came in way over forecast as well (computer models).
In the Illawarra, especially the northern suburbs, yesterday morning was ruined by katabatic-enhanced nor'westers.
Wasn't till mid-afternoon they backed off enough to make surfing possible. Shame as it was a particularly good swell.
It looked deadly out there in the morning. Hard pass.
Heard you gave it a go! I surfed at midday - half wind speed, still horrible, but much more manageable.
Yeah, paddled from the boat sheds in the dark with PBJ. Got one wave and called it quits.
hey stu can you loudly and repeatedly announce who you are when you're in the water just so next time i can say 'oh cool, that's stu from swellnet' when i'm out? okay thanks
I'll also make a neon sign.
beaut, just let me know what the sign says beforehand so i know it's you
Stu looks like a cross between Micheal Peterson and Gerry Lopez !
I scored 3 sick surfs in 3 day's
My local point a easy 8ft I would say bigger but thats frowned on in Sydney.
On Monday morning about 10am by the time I got my big step up ready changed
and paddled out roughly 1030 sets now 5ft. Wow half size twice the crowd
and way over gunned. Never seen a swell decline so quickly.
i did this once at cronulla point.. watched a monster roll through before first light, ran back to the car and grabbed my ridiculous gun and by the time i jumped out it was 4ft and i looked a FOOL, i tell you.
Greats photos Craig.
Thanks Sprout!
Great shots Craig !!!took some crazy pictures of some 8ft + waves exploding on shallow banks with white wash shooting 20ft up yesterday, same spot today surfed it at 2-3ft ..
Chuck em’ up sean
I’d love to goofy I’m totally shit technology ( dinosaur era) will found how so I can post them up
Easiest is using imagebb. Just google it and should explain it.
Took me a few goes to get it haha
Is there any other coastline in the world where this can happen Craig, or open to as many swell directions ?
I'd say New Zealand for one. Any real east coast actually that has lows forming off it. Also locations that get hurricanes and typhoons. So plenty.
I think from memory, it drops off pretty quickly at the Hobart Points
I was watching that foil lord from the headland - seriously big stuff
If you really want to get amongst the short-period-swell-that-only-lasts-a-few-hours then try surfing on the North Sea coastline for a few years. Get in the water for a couple of waves and then run back in to go for a quick Greggs sausage roll. By the time you put your wettie back on and wipe the crumbs of pastry off your chin the swell has totally evaporated. Like flat.
Ain't that true, lived in Aberdeen for a few years, was hard to work out
Great unique perspective of that spot. Awesome lens work
Cheers Ben!
I blinked.
Anybody heard how it went down the deep south that is really fickle or Tassie? Great pics Craig and the dreaded Green Cape kills it for those southerly swells the further you go south.
SE Tas. I got a wave Monday Morning before the wind hit and an average size, by Monday arvo I saw novelties I haven't seen in 5 years, and other spots twice the size I've seen before, all blown out by the wind. My local which rarely gets 3 ft, was an angry 6ft and unsurfable. More exposed spots were 12-15ft. Tuesday morning had halved in size to 6-8ft, but still solid, midday was 3-4ft, by 3:00pm I was on the 9'6 mal just to get the last few dregs after work.
Incredible eh, and especially the way it evolved and slammed into Tassie bringing that huge spike and then subsequent drop.
I've seen swells come and go quickly before, but never this size, and never from the east! Probably the biggest easterly in the last 5 years for Tas. Any data to back that claim up?
Also does the proximity have anything to do with the power of the swell? We always talk about a long period being powerful however in this instance it is relatively close but pumping from your photos (is that a foil on that right hander?).
Looking at single waves, no, they're no more powerful than the same sized swell and period from a distant storm.
Looking at groups of waves, sets and the sea state as a whole, much more energised, causing lots of current, sand movement etc.
Very nice Craig. Getting waves while overlooking a golf course is always a good shot, so much green and blue.
Looks like Long Reef golf course from my golf course knowledge, but could be wrong. There are a few up that way.
But what I really want to see from you Craig is a treatise on the phenomenal roll clouds on Tuesday. That’s another bucket list item ticked off for me, to see them, but I was driving west to east in the arvo and couldn’t get a photo so I just had to enjoy them.
What a sight! Never thought I’d see such a good example in Sydney, although did catch that one from a number of years ago that formed off Stu country and made its way up to Coogee.
But this one was 300 kms long, and 3 of them.
Wow, a Foil on 4 photo sequence. I can't quite believe it. Go Matt.