Melting Sea Ice Brings Rare Groundswell
It’s not often that the East Coast experiences groundswell periods in the high teens, let alone over twenty seconds, but one such swell is currently filling in across New South Wales.
While being open to swells from a wide variety of directions, the east facing nature of the aptly named East Coast is shadowed (Tasmania I’m looking at you) and angled away from the brunt of most Southern Ocean storms.
Savvy chart watchers and Swellnet readers would have been alerted to the fact that a flukey but strong south-southeast groundswell was due to build across southern NSW through today, with its source being a rare occurrence.
That being hurricane force winds inside the Ross Sea, below the Antarctic Circle at a latitude of 70° south. Swell generation in this region is rare as it's usually covered by sea ice, even through summer, but the last four years have been the lowest recorded Antarctic sea ice coverage on record - 2023 being the lowest on record.
The current sea ice extent chart as of March 23rd below shows a chunk of ice missing inside the Ross Sea - see chart below right. It also compares the current sea ice extent to the median extent from 1981-2010.
On Friday evening, we saw a significant polar low pushing east, far below New Zealand. On the southern flank of the low, a rare fetch of hurricane-force S/SE winds were produced in the Ross Sea, squeezing against the Trans Antarctic Mountain range directly to the west, setting in motion a strong, long-period south-southeast groundswell.
Sources: Weatherzone and NASA
This source is so rare that it's outside the range of our forecast WAMs and also outside of the scope of satellite scatterometer (wind) and altimetry (sea height) observations. Fortunately it was picked up by our forecaster team and shows in the forecast model output as a small but distinct, 20+ second groundswell.
Buoy observations picked up the leading edge yesterday afternoon off the southern New South Wales coast with periods sitting well over 20s, and since, the buoys further north have all picked up this strong groundswell and recorded peak periods between 19-21s.
Even the Tweed Buoy spectra is registering a faint signal of 22-23s swell.
Swell periods are correlated to the core wind speed within a swell-generating fetch, with the stronger the winds, the larger the eventual swell period as it travels away from the source.
With the source winds reaching an incredible 70-80kt, swell periods in excess of twenty seconds were always going to be the result, though the small and tight nature of these winds along with the large travel distance (over 4,000km) have only resulted in 4ft waves across the southern NSW coastline. The long-period nature is also resulting in super straight, beach-long closeouts that are more suited to reef breaks.
Macquarie Island situated due south of New Zealand would have seen the bulk of the energy with waves wrapping around both sides of the island. Similarly, Lord Howe Island in the middle of the Tasman Sea would have long period swell filling in on both sides.
As sea ice extent continues to shrink with a warming climate, we could possibly expect the frequency of these swells to slowly increase, though it’ll take a sharp eye to identify them from such a flukey source.
Comments
Far out.. that's pretty amazing
Will this work for Hobarts fickle points?
Nah too small.
Thought it was 1st April for a moment :)
crazytown! thanks craigo
Interesting article & confirms what I was watching this morning. Thought it was flat, then a strong pulse of swell out of nowhere, too straight for the banks though.
If I was still in Sydney I could have ventured down to Era point and possibly scored.
Not too much here early but has definitely picked through the morning...super straight and long waits...not much at all between sets and then some solid 4fter's to clean up the pack.
Great article again Craig!!
Great article Craig, very interesting. At 6.15am a cursory glance revealed nothing but 5 minutes of peering through the gloom showed it was definitely worth suiting up. Some fun ones before the wind and tide got into it.
My old local thrives on these Ross Sea swells, so I've been watching them for about 20 years. They're not that rare, thankfully.
Very nice.
Second that IB . I look out for pulses waaay south and hit a couple of south magnets that nobody knows of .
Just drove the coast around here and without any background swell we've got abject flatness punctuated every ten minutes by a set. A great novelty swell to watch but you wouldn't call it user friendly.
you see anything much of interest? i'm about to head out the local for a punt. for obscurity, it's a spot you'd hope was inaptly named.
*this message self-destructed*
That swell hit the Lower North Island NZ yesterday afternoon. Pumping today at various spots. We get something like between one and three of these a year. There is a very short window for them. Island Bay tuned me into them about ten years ago.
How good! Yeah they are rarely well aligned for the Australian East Coast so less common.
It's also an extra thousand kilometres of travel compared to Wellington (fifteen hundred more than Dunedin too) - and thus the additional swell decay.
It was 6-8ft where I surfed today. Very powerful. It's a spot that comes out of deep water and it really focusses the swell. Other spots nearby were 2ft. It was just one of those swells. I hadn't considered that a Ross Sea swell would make it to Australia, but it makes sense now I think about it.
Yep, true.
As Spuddups said, the peak season is short, and some years the Ross Sea never becomes truly ice free (one of my small daily jobs is to plot the ice edge in the S Pac). But even a 2/3 ice free Ross Sea opens up that window to longer period swells.
So good to see how one of Spuddups' favourites lit up today.
'Kin oath. It was one of those days you dine out on for months. It'll go into my surf diary as a 9/10.
Ha, got it!
Here's the Tweed signature picking up energy between 19-24s..
Fark, I love geeking out on swells and fickle spots etc.
Today's interesting NZ surf fact was that the west coast got an 18sec swell too. Rare double whammy.
And how pumping was today? Models under called? I saw shots of Lyall Bay cooking and wondered where that swell had come from. Fascinating. Hope you got your share
So good. Better than last Thursday/Friday, I reckon, and a lot less crowded. You get some?
Got one from outer boil Outsides to Keyhole (~900m according to google maps). My longest wave ever, easily.
Wow thats interesting.
Shame the wind was into, few bombies reefs starting to break
The new norm?
Arctic polar ice cap & Antartica melting.
Northern Polar bears & Southern penguins starving.
Extreme bushfires and floods across the planet.
4wds thriving.
"Reports from Bribie Island say that up to 1,200 4WDs hit the beach per day"
"The market has shifted with 4WDs now 46% of new cars (as of 2024), expected to top 50%..."
https://www.swellnet.com/news/swellnet-dispatch/2025/03/24/push-4wd-beac...
Enjoyed this swell with Spuddups today. Got excited when I saw it on the models. It takes about 3 days to get up here. You're right that the beachies don't like that much period, unless there's a great tapered bar. They tend to unfold too fast.
They don't tend to show here - but when they do, it's an insane angle for the points here if the bank is good.
No sign of anything here on dark.
Majority of Australian & Timor natural gas has been exported; to help O/S nations meet their required CO2 reduction targets & energy needs, since John Howard as Prime Minister signed a 30 year contract in 2002.
We received a gift of two giant pandas to Adelaide's zoo..... on loan
https://www.smh.com.au/opinion/how-australia-blew-its-future-gas-supplie...
3-5ft at a south swell location north of Newy on the mid north coast, straight lines n long lefts.......followed by 20-30mnutes of flatness!!
Well spotted Craig, great analysis. Sounds like a good explanation for a bit of 'surf magic' that happened when we were grommets. On a flat summer's day, early 1970s, at a reef break in West Oz, with nobody around, we burned a board as a sacrifice to Hughey, while jokingly chanting and praying for the conditions to change. Not long after, we watched in awe, as a set of waves from seemingly nowhere suddenly appeared and peeled off perfectly in front of our incredulous eyes. The very long interval, after that magic set, sure made us wonder. Apologies for chemical pollution in burning a board on the beach. We were optimistic, fun-loving, but very ignorant grommets indeed.
I love snooping around down there for crazy winds but never occurred to me it was supposed to be covered in ice. Thanks for the education!
I didn't get the chance to see the ocean this arvo, but hoping to find a few presents from antarctica in the water tomorrow.
The charts are horny for another fetch this weekend.
Yeah you spotted it last week!
Love this Craig thanks
Swell from a distant source
Hits south of the north with force
Antarctic swell watchers ditty
Ps -The southern Ocean maps are the most 'normal' looking Autumn I've noticed since Nina/Tonga Volcano.
Lucky to be at the in-laws in Wellington this week - not super familiar with the zone so just battled the circus at Lyall bay. Was super fun with surprisingly pleasant water temp.
Did anyone surf the points? I thought it would've been too small and went for a wedging back beach instead and got totally skunked. It was neither wedging or even breaking ok. This autumn sucks.