South-east Queensland and Northern NSW Surf Forecast by Ben Matson (issued Friday 18th December)

Features of the Forecast (tl;dr)

• Steady trade swell through into the weekend
• S'ly change spreading along Northern NSW during Sat, stalling near the border (N'ly risk ahead of it)
• Light winds across most regions for Sun though probably onshore at some point
• Long period E/NE cyclone swell could start arriving as early as Sun (mainly southern regions) but will be a slow grower through early next week
• Strong round of cyclone swell still on the cards from Tues thru' Thurs

Recap: Peaky 3-5ft trade swells have been largely wind affected from N’ly thru NE winds over the last two days, though there have been pockets of light winds at times, occasionally N/NW, allowing for temporarily clean periods at selected northern corners.  

No real keen on that water quality, eh.

This weekend (Dec 19 - 20)

No changes to the weekend forecast.

A S’ly change pushing up along Southern NSW this afternoon will reach the lower Mid North Coast early Saturday morning, and Coffs mid-late morning, before encroaching the Northern Rivers into the afternoon. I’m expecting it to stall near the border overnight and then dissipate into Sunday, so it probably won’t reach SE Qld.

Overnight N’ly winds ahead go the change should throttle right back into Saturday morning, though they’re likely to linger at a few coasts from time to time - mainly the Gold/Tweed Coasts - so keep your expectations low here. There’ll also be some leftover wobble from the last week of northerlies.

As for surf, we’re looking at a steady supply of E’ly swell from the ridge in the northern Tasman Sea. Open beaches should maintain 3-4ft sets from this source, and there’ll also be some local S’ly windswell in the wake of the change. Sunday may see a small mid-range S’ly swell across south facing beaches south of Byron, originating from W/SW gales exiting eastern Bass Strait today. Sets probably won’t top much more than 2-3ft from this source. 

Sunday's winds should become light and variable through the morning and will probably tend onshore at some point, though without any great strength.

As for cyclone swell potential - the entire weekend (mainly Sunday) is still a low confidence chance for the early forerunners originating from TC Yasa, mainly the Mid North Coast much more than anywhere else. 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, especially those in SE Qld.

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)

Coastal troughiness will dominate the region next week, leading to generally light winds most days though to begin with it’ll probably be some form of southerly in the south and northerly in the north, ahead of a more established southerly flow from Wednesday thanks to a developing ridge. 

Surf wise, 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 thru’ E’ly 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 towards Southern NSW, or 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 across open beaches, 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 Wednesday and/or Thursday. Either side, I’m hoping for slow, inconsistent 3-5ft sets by Tuesday afternoon, and also Thursday afternoon on the decline, with a gradual easing continuing into Friday. 

Regionally speaking, we’ll probably see the upper end of this size range across Northern NSW, with slightly smaller surf throughout SE Qld. You’ll also need to factor in a little less size across the points too. And, sets will be inconsistent - which is not a good fit with holiday crowds at the well known points.

Of course, actually surf quality is still up in the air pending the state of the sand, following this week’s bank busters. We really won’t have a proper understanding on that for a few more days. 

Anyway, it’s certainly a very positive swell outlook and local winds are shaping to be favourable for many regions so let’s check back Monday to see how it’s starting to fill in.

Have a great weekend, see you Monday!