Small tricky weekend; small NE swell Monday then series of strong S'ly swells next week

Ben Matson picture
Ben Matson (thermalben)

Sydney, Hunter and Illawarra Surf Forecast by Ben Matson (issued Friday 7th October)

Best Days: Sat: early session across Sydney's south facing beaches before the S'ly change. Mon: small peaky NE swell across exposed north facing locations. Tues onwards: series of building southerly swells, could become quite large Thurs/Fri.

Recap: As expected, Wednesday’s impressive short range south swell eased rapidly into Thursday, leaving very small surf for the morning. A new S’ly swell built slowly throughout the afternoon, and ended up coming just under size predictions though it was significant weaker and less consistent than anticipated. The reasons for this are related to the alignment of the responsible fetch, which I’ll try to detail over the weekend in an article, as it’s quite fascinating. Anyway, a second, much more powerful southerly groundswell pushed through this morning and seemed to reach a peak around the middle of the day. Many beaches have come in as expected (3-4ft south facing beaches, 5-6ft Hunter) but there are also quite a few locations that haven’t picked up the same level of energy, and are consequently smaller than forecast. The most likely reason for this is a phenomena known colloquially as (at least in the Swellnet office, anyway) “magic numbers”, whereby swells exhibiting particular swell characteristics - heigh, period, direction - are steered either towards, or away from ordinarily reliable swell magnets, due to the local bathymetry. This is also worthy of another article as it happens more often than you’re probably aware. I’ll see if I can tee up a more in-depth explanation in the future.

Newcastle on the pump this morning

This weekend (Oct 8th - Oct 9th)

Saturday’s expected S’ly change is due to reach the South Coast before dawn, and the Sydney region around 8-9am before pushing north into the Hunter before lunchtime.

Therefore, you’ll have to make the most of pre-frontal W/NW winds at dawn, which should keep most open beaches nice and clean for a brief period (obviously, a little longer across the Hunter). Today’s south swell is expected to ease back and it’ll only be surfable at south facing beaches with very inconsistent 2ft sets, becoming smaller during the day.

Surf size will be tiny at remaining beaches but there should be some bigger sets across the Hunter.

Saturday's southerly change won’t have enough strength to generate any major increase in size through the afternoon, however south facing beaches should see an increase in low quality windswell to 2ft or so late in the day. Tiny conditions will persist elsewhere.

This short range S’ly swell should hold into Sunday morning (inconsistent, average 2ft sets at south facing beaches, smaller elsewhere) and conditions should improve for the most part with light variable winds. 

A new S’ly groundswell is expected to arrive during the afternoon, sourced from the parent low to Saturday’s change as it tracks below Tasmania tonight. It’s not very well aligned but the fetch is broad, so south swell magnets should see a late pulse in the 2-3ft range (though, set waves will be extremely inconsistent, and it’ll remain tiny elsewhere). As per usual southerly groundswell events, the Hunter should see bigger waves - though the late timing of this swell may preclude any size advantages.

Of more concern on Sunday is that a strengthening high pressure ridge will drive freshening N/NE winds about the coastal margin after lunch, and may possibly reach strong to gale force strength by late in the day. As such only protected northern corners will see clean conditions. 

The upside is that we’ll see a small NE windswell build across the coast late afternoon, however it’ll probably be best utilised on Monday.

Next week (Oct 10th onwards)

Sunday’s strengthening northerlies will be associated with a massive slow moving, multi-centered, gyre-scale Southern Ocean low pressure system (see below).

These northerlies will generate a small windswell for the coast on Monday morning - possibly 2-3ft at reliable NE facing beaches in Sydney, but smaller across the Hunter and possibly a little bigger across the South Coast owing to the longer fetch length. 

The key to scoring good waves on Monday will be to wait for a westerly change to kick in - models have a pre-frontal trough ahead of the change, which should slacken off the northerly flow around dawn, veering NW in direction through the morning, before moderate to fresh W’ly winds pick up after lunch. So it’s hard to estimate when the best waves will occur as the afternoon’s westerlies will probably occur as the swell starts to lose some size. I’ll update in the notes below with the availability of updated model guidance. 

As the broadscale low moves east, its western flank will eventually slide into our southern swell window and this is expected to generate a series of southerly groundswells for Southern NSW for the rest of the week

The first swell is due on Tuesday - short range energy from a strong SW fetch exiting eastern Bass Strait - but larger, more powerful south swells are likely through second half of the week as intense secondary fronts track up into the lower Tasman Sea. 

At this stage I’m hesitant to put down any specifics, as the models are moving around a lot, but early indications are than Thursday afternoon and Friday could see some very large waves in the 6ft+ range or bigger at south facing beaches. 

In addition to this, I'll also be keeping an eye on a developing tropical system south of Fiji early next week which has the potential to supply a brief, small to moderate E/NE swell for the NSW coast around Thursday or Friday next week. 

So, there’s plenty to look forward to in the long term outlook - check back Monday to see how it’s all tracking. 

Have a great weekend!


black-duck's picture
black-duck's picture
black-duck Friday, 7 Oct 2016 at 10:18pm

"gyre-scale Southern Ocean low pressure system"
Always some joy in reading your forecast notes.

thermalben's picture
thermalben's picture
thermalben Saturday, 8 Oct 2016 at 7:04am

Thanks.. nice to find a new term to use!

thermalben's picture
thermalben's picture
thermalben Saturday, 8 Oct 2016 at 7:05am

You gotta be patient this morning. But there are waves, occ 2ft sets at Bondi and a little bigger in Newy. Slim pickings on the whole though.

alexsmith1's picture
alexsmith1's picture
alexsmith1 Saturday, 8 Oct 2016 at 10:19am

Timing was spot on with the south winds on the NB.. Few fun 2ft runners before the wind destroyed it. Hopefully we see some nice lines tomorrow arvo

thermalben's picture
thermalben's picture
thermalben Sunday, 9 Oct 2016 at 8:10am

Not sure whether this is the afternoon's southerly groundswell arriving earlier, and a little bigger than expected? But there are solid 3ft+ sets about the coast this morning. Looks like groundswell to me though the waves are closely spaced together, and there are overlapping swell trains too.

thermalben's picture
thermalben's picture
thermalben Sunday, 9 Oct 2016 at 2:25pm

Bondi looks a little smaller than earlier; winds are now up from the NE.

thermalben's picture
thermalben's picture
thermalben Sunday, 9 Oct 2016 at 6:09pm

'Bout the same at Bondi this morning. Looks like the groundswell may have in fact peaked this morning, well ahead of schedule. Small NE wind waves across north facing beaches too, which should build further overnight, hopefully into something respectable just before the wind swings W'ly.

thermalben's picture
thermalben's picture
thermalben Monday, 10 Oct 2016 at 12:17pm

The NE swell is still holding, and winds are now light N'ly so conditions are slowly getting better though it hasn't swung offshore yet. Still looks a good 2-3ft too.