Large cyclone swell ahoy!
South-east Queensland and Northern NSW Surf Forecast by Ben Matson (issued Monday 18th February)
Best Days: Large swells developing Wed arvo onwards (SE Qld, Far Northern NSW) becoming very large into Thursday, smaller south from Ballina. Difficult to have confidence Friday onwards, though it'll likely remain windy out of the south, and most likely quite solid out of the east for a few days at least.
Recap: Great waves over the weekend with a strong E/SE swell building to 5-6ft across some exposed coasts later Saturday and early Sunday, easing slowly through the day and edging back a little more today. Winds haven’t been too much of a problem, some regions even saw light winds on Sunday afternoon but in general it’s been early S’lies tending moderate to fresh SE or even E (Saturday saw the most strength).
Lunchtime barrels behind the rock at Snapper. The sand's back!
Even Narrowneck was looking fun this morning
This week and weekend (Feb 19 onwards)
TC Oma is a complex system that’s been fascinating to watch over the last few days, mainly because of its slow moving nature in and around the Vanuatu region.
As for swell potential, there’s a lot of mis-information in the model guidance, for a couple of reasons.
Firstly, TC Oma lies to the north of New Caledonia, and although it looks (on the charts) that there’s a clear swell window through to at least SE Qld (and at a pinch, various parts of the NSW coast), in fact there is an otherwise sneaky, hidden obstacle - the French archipelago known as the Chesterfield Islands, lying approximately 550km NW of New Caledonia. They are sufficiently broad in spatial coverage to present a significant barrier to any E/NE or NE swell from locations upstream (i.e. close to Vanuatu).
Therefore, with the Gold Coast data point estimating the leading edge of cyclone swell to arrive this morning (0.3m @ 16.3 seconds NE, around 6am), I have to call bullshit: TC Oma won’t really clear the New Caledonian swell shadow until tomorrow, and even then most of the core fetch won’t be ideally aimed within our swell window. It's simply picking up swell energy forecast by a wave model that doesn't have the appropriate archipelago masking.
So, with the wave model building this NE swell component (as an individual swell train) into Tuesday, we need to be extremely cautious about our expectations. Because if my estimation that the Chesterfields will block most NE swell generated yesterday and today is true, then Tuesday should mainly E/SE swell from a moderating ridge in the northern Tasman Sea (responsible for our weekend’s lovely waves) plus a small spread of E/NE swell from the supporting ridge below TC Oma.
Let’s peg the open beaches across SE Qld and Far Northern NSW around the 3-4ft+ mark, easing slightly during the day, with smaller surf along the points and also south from Ballina. Light winds and afternoon sea breezes are expected in the north but the Mid North Coast will see moderate, freshening N’ly winds as a shallow southerly change pushes up the Southern NSW coast and then stalls.
The cyclone should enter our swell window on Tuesday morning which makes Wednesday the first plausible day to see any proper cyclone swell, but even then the morning will probably see more size from the supporting ridge, because the fetch length of core (cyclonic) winds will be rather short.
At this stage we're looking at undersized surf across SE Qld and Far Northern NSW (3ft+ open beaches), but stronger cyclone swell should start to arrive into the afternoon. At this stage - without the availablity of satellite observations to confirm wind speeds and active quadrants - we can really only go on model guidance, this suggests a kick into the 6ft+ range by the end of the day (may not be until overnight, south from Ballina or Yamba though). Winds should be light early but will freshen from the S/SE throughout the day (strongest in the north).
From here on, things get very tricky.
And this is because of a recent major divergence in model guidance.
On Friday, the general consensus had firmed that TC Oma would following the climatological convention, briefly push into SE Qld coastal waters, and then be deflected to the south-east enroute to New Zealand, where it’d undergo extra tropical transition. We’d see large (or very large) NE tending E’ly swells mid-late week as it glanced our region, ahead of a strong SE swell off the latter stages of the low near New Zealand.
This outlook held into Saturday and early Sunday. Confidence continued to build.
On Sunday evening, the world’s leading atmospheric model (ECMWF) bucked the trend: keeping TC Oma off the SE Qld coast for a few days and then actually tracking it north, ahead of a coastal crossing mid-next week.
This is quite the curveball.
So, I’ve been patiently waiting for the latest model update (hence the delay on these notes). And they seem to be holding steady with this divergent view. ACCESS G is also siding with EC, so it's now impossible to find a line of best fit.
In the short term, this won’t have a material impact on the forecast for SE Qld and Far Northern NSW coasts for Thursday at least, and maybe Friday: we’re looking at strong southerly winds in all regions and large E/NE swells from TC Oma. The cyclone itself seems to initially tick many boxes: very strong winds, slow moving system, ideal distance off the coast, fetch reasonably well aimed etc, so the chances of a large swell event are pretty good - though core wind speeds are down a lot from Friday’s estimates. So I think we’re probably looking at Thursday building into the 8-10ft+ range at exposed coasts (smaller at protected spots). Surf size will however become smaller as you track south from about Ballina or Yamba.
There'll be a LOT of water moving around though, and with the north-east component in the water, we'll see 'trapped' conditions across some of the southern bays and points (compared to the more sweepy SE or S'ly swells of size). So, make sure you're confident in your ability before you paddle out.
The main different between model runs is that the GFS solution presents a smaller peak in energy (though lot of southerly windswell in the wake of the cyclone swell, owing to a strong coastal ridge), but the EC solution maintains large cyclone swells for quite a few days.
In fact, there’s even a suggestion it may move further north back into the Coral Sea, and eyeball a possible coastal crossing in and around the Capriconia coast. Sure, it's a while away but anything is possible at the moment.
So, instead of elaborating any further on the long term trend beyond Thursday, let’s take another pass on Wednesday.
I’ll also update in the comments below tomorrow if anything new comes to light.