Steady diet of nothing but south swell

Ben Matson picture
Ben Matson (thermalben)

Sydney, Hunter and Illawarra Surf Forecast by Ben Matson (issued Monday 21st February)

Best Days: Wed/Fri: large to very large long period S'ly groundswell with generally light winds. Tues/Thurs/Sat: medium size S'ly surf (between main swell events) with good winds excluding Tues PM. Sun: Another solid S'ly swell, though smaller than the last few. 

Recap: There’s been stacks of southerly swell over the last few days. Saturday saw 3-5ft sets across Sydney’s south facing beaches with a few bigger bombs reported elsewhere, but size eased throughout the day. A reinforcing S’ly swell maintained 3ft sets at south facing beaches into Sunday (slightly bigger on the Hunter) whilst a marginally bigger third swell pushed through into today, increasing south facing beaches to 3-4ft whilst providing bigger waves throughout Newcastle once again. Offshores maintained clean conditions throughout.

Today’s Forecaster Notes are brought to you by Rip Curl

This week (May 22 - 25th)

We’re in the midst of a strong autumnal south swell pattern, with no signs of any let up in the near future. In fact it looks like we’re going to go up another gear or two as we progress into the end of the week and beyond, related to a slow moving node of the Long Wave Trough.

We’re staring down the barrel of back-to-back long period southerly groundswells, each offering varying levels of size, period and degrees of southerly direction. Initially, Tuesday should see continuing mid-range energy from a persistent SW fetch exiting eastern Bass Strait for the last day or so (similar to the surf we’ve seen today; say 3ft+ south facing beaches in Sydney and 4-5ft across there Hunter), but it’ll be overshadowed by a stronger S’ly groundswell into the afternoon, generated by a powerful front rounding the Tasmanian corner today.

This front is displaying very strong winds in excess of 40-45kts but more impressive is the length and fetch of the width, its relatively slow core forward speed (for a Southern Ocean front) and a slight meridional (north-south) tweak in its alignment through the lower Tasman Sea as we head into Tuesday.

Initially, Sydney beaches should see a building trend from the head of the fetch into Tuesday afternoon (earlier down south) that’ll ratchet up wave heights by a foot or two - but this is by no means the strongest part of the system: Wednesday morning is looking at an almighty pulse of powerful long period southerly swell that’ll light up south swell magnets with very big surf in excess of 6-8ft+. I think our surf model is pretty close to the mark with this one though it’s got the peak into the afternoon, whilst I think it may occur a little earlier (that being said, it’ll remain large all day). I reckon we’ll see some very large waves ridden at some of the more reliable offshore bombies well above this height prediction too (i.e. pushing 8-10ft+). 

The other points of interest for Tuesday and Wednesday are the winds: Tuesday should see early W/SW winds swinging S/SW into the middle of the afternoon (earlier down south) as the edge of the front clips the coast. This should clear Wednesday to a light variable pattern with afternoon sea breezes, though some regions north of Sydney such as the Hunter may see a lingering southerly through the morning. 

And just on wave heights: it’ll be much smaller at beaches that don’t face south, and it’s common to experience a wide variation in size from beach to beach, depending on exposure and bathymetry (as per Craig’s excellent article from last week Analysis: The long and the short of long period swells). But no matter how you slice it, Wednesday is looking pretty big and beefy so even protected spots should have workable waves. 

It doesn’t end there. 

Thursday will see a rapid drop in size from Wednesday, though still remaining elevated across south facing beaches with sets around 4-5ft (bigger across the Hunter near 6ft+). Surface conditions should be quite clean with light variable winds and light afternoon sea breezes. Beaches not directly open to the south will be much smaller.

Whilst this is happening, an even more powerful Southern Ocean low will have developed south of Tasmania, and is expected to slingshot through out far southern swell window, broadening and lengthening an impressive fetch of storm force SW winds through the southern Tasman Sea into Thursday morning. 

If anything, this swell looks a little better on paper with stronger core winds, though it’s alignment isn’t quite as good as the fetch generating Wednesday’s swells. This will translate to larger swell periods but with slightly less ocean size at the coastal margin - arriving Friday, becoming largest into the afternoon - which will probably in turn exaggerate the variation in wave heights across the coast even more from our mid-week event. 

So, those handful of offshore bombies and other reliable locations that accentuate long period south swells particularly well should be larger again - perhaps north of 10ft+ at times - but regular south facing beaches will probably max out in the 6ft+ range, whilst everywhere else comes in much smaller. Again, I need to reiterate the fact that there'll be large discrepencies in wave heights from coast to coast. Despite being a stronger system, this swell won't be aimed as well for Southern NSW and so this time around, a smaller percentage of locations are likely to pick up the bulk energy.

Friday’s winds look really good too under a slack pressure gradient, just light and variable. 

So, in summary - Wednesday and Friday are your biggest days this week. Great conditions are expected most of the period except late Tuesday and maybe early Wednesday at a few spots. 

This weekend (May 26 - 27)

Friday’s large southerly groundswell will ease slowly through Saturday though remain very solid across south facing beaches. Early sets should still be up in the 4-6ft range but it’ll abate to 3-4ft throughout the day (expect another couple of feet across the Hunter). Light winds are expected to maintain smooth conditions.

Into Sunday, yet another long period S’ly swell will grace the coast but this time ‘round it’ll be from a less favourably aligned system pushing through the south-eastern corner of the lower Tasman Sea (plus a little further south in latitude) so we’ll see smaller size than our last few long period swells. 

That being said, it won’t be small by any measure - back up into the 4-5ft range at south facing beaches and 6ft+ across the Hunter throughout the day. A slow moving ridge of high pressure should maintain light winds across the coast. Surf size will once again be smaller at beaches wit less southerly exposure.

So yeah - a steady diet of nothing but southerly swell.  

Next week (May 28 onwards)

This entire progression of southerly swells - related to a slow moving node of the Long Wave Trough - will migrate to a position off New Zealand’s East Coast next week, whilst our Tasman swell window shuts down for a brief period. We may see some flukey long range SE swells from this LWT pattern but there’s nothing noteworthy on the long term carts at this stage. 

Comments

stunet's picture
stunet's picture
stunet Monday, 21 May 2018 at 6:27pm

"What once was promised, now will be ."

surfads's picture
surfads's picture
surfads Monday, 21 May 2018 at 7:20pm

1, 2, 3 Repeater

JDevil's picture
JDevil's picture
JDevil Monday, 21 May 2018 at 8:39pm

I've been looking at the wind forecasts (windwilly, BOM, Swellnet) and have found them less predictable this time of year.

Anyone else notice this? Today has mostly seen W/NW, yet was predicted as SW winds. What throws these forecasts off? Is it from multiple pressure systems in one area?

Craig's picture
Craig's picture
Craig Monday, 21 May 2018 at 8:47pm

Looking at the hi-res modelling and it's had W-W/SW most of the day which is as what's recorded around Sydney and by our model..

Craig's picture
Craig's picture
Craig Monday, 21 May 2018 at 8:50pm

Looking at tomorrow I reckon there's a high chance of W/NW winds across the region, looking at this (very small in-flex)..

Hi-res models pick it up, lower res just show W-W/SW.

Always have to look a little deeper if you want macro forecasts..

JDevil's picture
JDevil's picture
JDevil Wednesday, 23 May 2018 at 10:08am

It looks like a difficult judgement to make when further inland is blowing SW and way offshore is blowing SW. Only near the coastline is W/NW.

It looks like the edge of two systems creates different wind patterns.

So I should really look at the forecast for a region e.g. Sydney-Hunter, instead of suburb forecasts to get a picture of what should be happening.

blindboy's picture
blindboy's picture
blindboy Monday, 21 May 2018 at 8:58pm

It was a weird wind today, SW but as warm as NW at times.

Craig's picture
Craig's picture
Craig Tuesday, 22 May 2018 at 6:04am

Yeah wasn't it. Left home in a jacket and quickly chucked it off.

Craig's picture
Craig's picture
Craig Tuesday, 22 May 2018 at 6:04am

W/NW winds this morning :)

shoredump's picture
shoredump's picture
shoredump Tuesday, 22 May 2018 at 6:05am

Autumn is in bloom! :)
I’ve still got some flowers on my frangipani tree, they were all gone by late March last year

blindboy's picture
blindboy's picture
blindboy Tuesday, 22 May 2018 at 5:11pm

Couldn't see any sign of that predicted stronger swell this arvo. Very similar to this morning. Undersized and weak. Given the models have over called Monday and Tuesday, does anyone want to call tomorrow? Me, relying on traditional methods, (sniff the air, study the horizon, watch the clouds) I am calling under sized again. Maybe 3-4ft at best, but would be very happy to be proved wrong.

Craig's picture
Craig's picture
Craig Tuesday, 22 May 2018 at 5:23pm

Yeah def drop in swell by mid-morning today and much weaker than yesterday.

Late today's swell was from a fetch pushing up the coast which looks a little delayed, and has also brought with it some funky winds tomorrow morning, groundswell should be strong through the day though. Bigger than 3-4ft, but spots seeing size will be average..

blindboy's picture
blindboy's picture
blindboy Tuesday, 22 May 2018 at 5:45pm

Thanks Craig, I am not so sure about the drop this morning. There was a super long lull around 10.30, then came again briefly, then another long lull. Just when you thought it had given up it would throw another couple of 3 footers into the mix, but seriously under powered, walking pace!

thermalben's picture
thermalben's picture
thermalben Tuesday, 22 May 2018 at 6:27pm

Just 3-4ft tomorrow?

No chance. That's one heck of a system powering through the southern Tasman Sea right now.

Can't wait to see the ASCAT images tomorrow morning from this afternoon's fetch.  

blindboy's picture
blindboy's picture
blindboy Tuesday, 22 May 2018 at 7:11pm

Hope you're right Ben!

billie's picture
billie's picture
billie Tuesday, 22 May 2018 at 6:40pm

Cool. Thanks for engaging in the conversation Ben! I was looking at the waves on sark thinking.......? 10 foot my ass! Im so frothing on tomorrow.

Whaddya reckon the period will be tomorrow?

thermalben's picture
thermalben's picture
thermalben Tuesday, 22 May 2018 at 6:53pm

The swell period matters, but then it doesn't matter very much at all.

I could tell you: I think peak swell periods are going to be 16-17 seconds tomorrow. 

But that doesn't mean anything without context. 

Peak swell periods were 22 seconds at the Tweed Heads buoy on Saturday. 

22 seconds! I hear you gasp for air. Ain't that Hawaiian-style swell periods? Must have been massive!

Yeah, nah. Surf was 1-2ft on the Gold Coast Saturday. Couple of 2-3ft sets at exposed northern ends. Bigger in Northern NSW (5-6ft sets) but my point is: the value of the swell periods is somewhat meaningless without context.

And, it doesn't suit every surf break (or coastline) either.

billie's picture
billie's picture
billie Tuesday, 22 May 2018 at 6:42pm

Also, quick question. I have noticed often the swell period jumps dramatically from 10seconds to 16 seconds, tomorrow is an example. Is this because a ground swell suddenly swings into the window and arrives suddenly?

thermalben's picture
thermalben's picture
thermalben Tuesday, 22 May 2018 at 6:48pm

Just a new long period groundswell overtaking a previous older groundswell (which has faded, and thus has lower periods).

billie's picture
billie's picture
billie Tuesday, 22 May 2018 at 7:05pm

So it doesn't jump suddenly but as one drops and another rises the primary swells period is used as the measure?

I got my eye on a spot tomorrow that only loves a south swell when the period is long. Quite excited actually.

Thanks!

billie's picture
billie's picture
billie Tuesday, 22 May 2018 at 7:07pm

Or is it that a dying swell has a lower period? No, it could easily work both ways huh? A dying swell due to a system moving away from the coast (though still a substantial swell) would have a longer period than the same swell when closer. Right?

billie's picture
billie's picture
billie Tuesday, 22 May 2018 at 7:09pm

Is this pretty much part of the conversations amongst students and lecturers when you were at uni when studying swell periods?

billie's picture
billie's picture
billie Tuesday, 22 May 2018 at 7:47pm

Looking at BOM's current synoptic for 6pm, is the swell source outside of view? Im a bit excited , I know. Sorry

blindboy's picture
blindboy's picture
blindboy Tuesday, 22 May 2018 at 8:31pm

If you are not familiar with Manly Hydraulic Lab, have a look here. Lots of info.
http://www.forecast.waves.nsw.gov.au/index.php?init=1&cont=10&zoom=7&mod=20

Halfscousehalfcockneyfullaussie's picture
Halfscousehalfcockneyfullaussie's picture
Halfscousehalfc... Tuesday, 22 May 2018 at 8:51pm

Should be interesting to see what happens to the sand banks after this swell. That swell improved the sand heaps at my local created a few more rips here and there which created a couple of new banks.

thermalben's picture
thermalben's picture
thermalben Wednesday, 23 May 2018 at 10:22am

Looks like the swell's running a little late, but already showing very strong south of Sydney.. reports of 8ft sets across the Illawarra. Should peak after lunch and through the afternoon.

chook's picture
chook's picture
chook Wednesday, 23 May 2018 at 4:26pm

such a fater lunch it was still pretty clean, but a bit of wind had come up. pretyy much all closeouts. lots of backwash from the beach and cliffs..a wave is running north-south, making a near pefect right angle when it crosses the incoming waves.

evosurfer's picture
evosurfer's picture
evosurfer Wednesday, 23 May 2018 at 4:38pm

Well it was onshore by 0900hrs and the swell well no great long lines at a big period
where I am, it is bigger than yesterday but rubbish another great disappointment.

blindboy's picture
blindboy's picture
blindboy Wednesday, 23 May 2018 at 4:43pm

Had a few fun 4 footers late morning. Picked up a little later but quality deteriorated. Seriously under powered for its size. Sets on the outside Bommie might have got to 8ft but nothing much over 5ft inside.

stunet's picture
stunet's picture
stunet Wednesday, 23 May 2018 at 5:03pm

Southern end of the Coal Coast = 4ft, northern end = 8ft.

No problem with size if you're somewhere exposed. The surprising thing was the indistinct lines; I thought this swell was gonna be ruler-sharp and marching but it's fluffy and on the wobble.