Sydney, Hunter and Illawarra Surf Forecast by Ben Matson (issued Friday 18th December)

Features of the Forecast (tl;dr)

• Weekend outlook: average conditions Sat AM though with plenty of E/NE swell, better Sun with light winds
• Long period NE cyclone swell chould start arriving as early as Sun but will be a slow grower through early next week
• Strong round of cyclone groundswell still on the cards Wed/Thurs though there'll be fun waves regardless from Tues through Fri

Recap: 3-4ft E/NE swells over the last two days coincided with moderate to almost fresh N/NE winds on Thursday, but light variable tending NW winds today, which has clean up conditions nicely. A gusty S’ly change went through Kiama around 3pm.

Moody blues on the Coal Coast this arvo

This weekend (Dec 19 - 20)

No changes to the weekend forecast with lingering S/SE winds on Saturday morning likely to take the sheen off surface conditions. 

We’ll see a continuing mix of E/NE swells (3ft or so at open beaches, a little inconsistent) and a mix of S’ly swells too - some short range energy trailing the change, and a slightly longer but more acute S’ly swell from W/SW gales exiting eastern Bass Strait today. South facing beaches should pick up occasional 2-3ft sets, with bigger (but very bumpy) options in the Hunter.

Winds will throttle back quickly and the afternoon should be under 10kts across most locations, especially south from Sydney, so there’ll be fun lumpy waves for the late session. 

Sunday’s looking at a smaller mix of leftover (and easing) S’ly swell, plus residual E/NE swell holding occasional 3ft sets at exposed beaches. A modest developing E/SE fetch on the southern flank of a broad trough across the central Tasman Sea may kick up some small mid-range energy but I don’t think there’ll much in it.

Light variable winds are expected for most of Sunday though there is a risk of a moderate N’ly at times; model guidance is suggesting this may only affect the Illawarra and South Coast but it’ll be worth keeping an eye on things. Shouldn’t be too strong if and when it comes up though.

As for cyclone swell potential - the entire weekend (mainly Sunday) is still a low confidence chance for the early forerunners originating from TC Yasa. It’s quite likely that some energy will be pushing through the guts of the Tasman Sea over the weekend, but because the initial source of this energy was tucked up inside the narrow swell window between New Cal and Fiji, the long travel distance means perhaps a handful of super exposed locations might pick up slow 2-3ft sets at best. Most spots will probably dip out.  

So, even if Tp values on the buoys spike, this energy might be pretty hard to detect in the water, as it’s expected to be a faint, inconsistent signal at best. But still, it’s worth keeping an eye out for.

Next week (Dec 21 onwards)

Sunday’s weak trough still isn’t expected to develop into much of a Tasman Low and the resulting surf outlook from it is nondescript.

As such, all eyes remain on Severe TC Yasa, which recently passed over Fiji and has now properly entered our swell window.

First things first - I’m normally quite skeptical about swell potential from tropical cyclones, and prefer to downplay surf prospects unless there’s a lot of supporting evidence elsewhere. In the case of Severe TC Yasa, there are actually quite a few positives but also a few negatives.

Firstly, the positives. Cat 5 status doesn’t mean much from a distant tropical cyclone (re: surf potential), as the width and length of the core fetch (and thus the strongest winds) is very small, and probably won’t contribute the bulk swell energy. So therefore we can look at the synoptics in a different manner - and even though STC Yasa is expected to weaken steadily over the coming days, the diameter of the primary supporting fetch - say 30-40kts - is expected to remain steady, and even by Monday there should be a reasonable E/NE fetch left in the western South Pacific, north of New Zealand.

The storm track is pretty good too; slow, to the south, then a recurve to the south-west and then west. It looks to be a little too slow (and a little too far away) for a useful captured fetch scenario, but regardless, I like what I see.

OK, now for the negatives. Model guidance has slowly edged the broader storm track to the east over the last few days, pushing it slightly further away form the Australian mainland with each successive run (bumping up the wave decay each time). So, this will increase the inconsistency of the resulting swell and also pull back potential peak wave heights. It's also unsure whether STC Yasa's strongest quadrant will be aimed in our region, or more towards SE Qld. But that's a gamble I'll have to take right now, and then assess over the weekend via ASCAT.

So, on to the main event. Getting the timing right is difficult, because it appears that there’ll be several pulses arriving throughout the course of four or five days. If we dismiss Sunday’s potential, Monday should see a slow increase from 2-3ft to 4ft through the day, and each day thereafter has some form of energy renewal on the cards - but getting the timing on each one is pretty much impossible. Sure, this might look like fence sitting, but there’s simply no way to have error bars of only a couple of hours when the swell source is a dynamic event thousand of kilometres away.

In broad terms, the biggest pulse of the event could produce 5-6ft waves at exposed beaches, and this is *fingers crossed* pegged for later Wednesday or Thursday. Either side, I’m hoping for slow, inconsistent 3-5ft sets by Tuesday afernoon, and also Thursday afternoon on the decline, with a gradual easing continuing into Friday. 

The good news is that there are no local synoptic drivers expected all week - a S'ly change overnight Tuesday may linger into Wednesday but should clear quickly - so winds should be relatively light most mornings (except Wednesday) and you should be able to hunt down decent options most days. Xmas Eve/Day are certainly looking pretty tasty!

Have a great weekend, see you Monday.