Sydney, Hunter and Illawarra Surf Forecast by Ben Matson (issued Monday 23rd December)

Best Days: Tues: strong though inconsistent S'ly swell, easing, early light winds. Next week: potential NE cyclone swell. 

Recap: Saturday delivered building NE wind swells into the 2-3ft range by the afternoon (smaller earlier) ahead of a S’ly change that reversed the swell direction for Sunday, with south facing beaches picking up 2-3ft sets. Overnight, the leading edge of a long period S’ly groundswell reached Southern NSW and the Port Botany buoy detected peak swell periods of 21 seconds. This swell is now building across the region; sets are already an inconsistent 3-5ft at south facing beaches though we're still quite some time away from the likely peak.

This week (Dec 24 - 27)

There are couple of reasons why my Forecaster Notes are usually delivered mid-late afternoon, instead of earlier in the day. And today is a good example.

Right now we’ve got a tricky, unusual long period S’ly swell building across the coast. It’s different to many swells because we’re expecting several pulses of overlapping long period energy to arrive over the space of 24-36 hours (instead of an initial peak, then plateau followed by steady decline) - and in Friday’s notes I had estimated a peak in size later today and/or early tomorrow.

As such, I would greatly appreciate the ability to monitor the day’s trend before preparing these notes. But, I’m time-poor today, so without such luxuries, I’ll have to go with my gut.

We don’t have any upstream data that can be used to accurately confirm the inbound swell trend - other coasts that have already picked up this swell (SA, Vic, Tas) were better aligned to the swell source compared to Southern NSW so we’ll see a different response along the East Coast because of the extra work required for the swell to bend back into the mainland. 

Nevertheless, some very large waves were reported across southern coasts yesterday (in addition to the array of wave buoys) so I really don’t have any data that leads me to change Friday’s projections. Which is: a peak later today or tomorrow, with a much greater size range between exposed/protected coasts than under normal south swells.

South facing beaches should pick up 5-6ft sets at the height of the event, but a handful of offshore bombies and south swell magnets like the Hunter still have the potential for sets in and around the 8ft mark (they'll certainly be the exception rather than the rule). But, any beach not exposed to the south will be much, much smaller - this is a much less reliable southerly swell than normal, so your local beach may not respond in the normal way due to the unusually large swell periods. And set waves will be quite inconsistent too. 

Local winds look to be below average for the next few days, though we’ll see pockets of light variable conditions at times. However, moderate E’ly through NE winds are likely across most coasts some point under the influence of a weak coastal trough. So keep in mind: conditions won’t be perfect. Wednesday afternoon looks to be the most wind affected, Tuesday morning the least.

Whatever size is reached at its peak, the southerly swell will steadily ease through Tuesday afternoon and Wednesday. At the same time, a peaky short range E/NE swell (sourced from a small infeed into the coastal trough) will provide occasional 2-3ft sets to exposed beaches mid-week.

Thursday and Friday are then looking at smaller background swells from the E/NE (minor trade swell from the South Pacific) and some residual S’ly swell too. And a persistent NE fetch adjacent the coast for the rest of the week will maintain small NE windswells, whilst also keeping a lid on surf quality too. Again, there’ll be pockets of lighter winds - mainly the mornings - but it won’t be fantastic.

This weekend (Dec 28  - 29)

A Tasman high pressure system later this week will build a ridge through into the Coral Sea, and we’ll see a minor trade swell for the weekend - in addition to the (very inconsistent) distant trade swell generated by E’ly winds NE of New Zealand over the coming days. 

A tightening of the pressure gradient off the Central NSW coast from Friday onwards will also generate a peaky NE swell for Southern NSW, with size likely to reach 2-3ft at times. 

A series of very poorly aligned fronts through the Southern Ocean later this week will generate minor S’ly swell for exposed beaches though I don’t think we’ll see much size. 

Local winds look to be influenced by the Tasman high; that is, mainly NE all weekend - though a small trough may push up the South Coast, disrupting the northerly flow across some regions. I’ll have a better idea that in Wednesday’s update. 

Next week (Dec 30 onwards)

As mentioned in Friday’s notes, a Tropical Cyclone is expected to form north of Fiji around Xmas Day or Boxing Day. Current expectations have it tracking south, finally entering our swell window this Friday or Saturday.

The latest model projections have this as a large, slow moving system between New Zealand and Fiji for a few days - which is very exciting - though with a slow E’ly track (see below). Normally this would have an adverse effect on surf potential, however at this stage it shouldn’t be too detrimental, given its duration within our swell window. 

As such, I'm expecting a NE cyclone swell to arrive around Monday 30th, holding for a few days into the New Year (so, potentially a three or four day swell event). However, there’s not a lot of confidence in how much size we’ll see - it does indeed look like being a big, beefy system - but the strongest winds are modelled to be on its western flank, aimed towards Vanuatu.

We will see the model guidance swing around over the coming days (at the moment, our surf model is only estiating 2-3ft surf), and I’m reasonably confident that we’re looking at some excellent, solid waves in and around the turn of the New Year. Let’s ballpark peak size for this event around the 4-6ft mark for now, and revise the outlook over the coming days.

See you Wednesday!