Curveball-o-rama: TC Oma swell outlook on hold
Sydney, Hunter and Illawarra Surf Forecast by Ben Matson (issued Monday 18th February)
Best Days: Everything's on pause right now. Can't see a good day this forecast period with any clarity right now.
Recap: Saturday saw a peaky mix of fun S’ly swell around 2-3ft, plus some E/NE swell of a similar size. Light winds gave way to afternoon NSW sea breezes. Unfortunately, Sunday didn’t pulse in size as expected from the E/NE (despite the Mid North and Northern NSW coasts building nicely), maintaining 2ft waves through the morning before increasing slightly to 2-3ft throughout the day. Early light winds were then followed by fresh NE winds. We’ve seen the E/NE swell combine with a peaky NE windswell today, offering 2-3ft waves across the coast. A small S’ly swell is also providing occasional 2ft+ waves to south facing beaches. A brief period of light N’ly winds have freshened from the NE throughout the day.
Small punchy NE/E/NE swell combo at Maroubra this arvo. Shame about the wind.
This week and weekend (Feb 19 onwards)
Before we get into the discussion re: TC Oma, it’s looking like today’s small south swell will ease from Tuesday onwards. Not that there’s a lot of size anyway.
A series of poorly aligned Southern Ocean fronts will provide minor background southerly groundswell all week, and a shallow southerly change will bring about a local windswell increase once it pushes through on Tuesday morning (building into the afternoon, easing through Wednesday, low quality sets peaking around 2-3ft+). Don't get your hopes up.
Righto. On to TC Oma.
It’s been a fascinating system 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 Northern Beaches data point registering the leading edge of cyclone swell on Tuesday (0.2m @ 14.9 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 the model that doesn't have the appropriate archipelago masking.
In fact, for the next few days once TC Oma enters the swell window, it really won’t be sitting in a prime position for our coast (fetch alignment will be on the wrong quadrants), so I’ve downgraded my thinking from Friday’s notes: we’re probably looking at an eventual spread of small to moderate E/NE swell, mainly source from the supporting ridge to the south, but probably arriving later in the week. Actual long period NE swell is now unlikely to eventuate.
But, to be honest most of the forecast period from Thursday onwards is a write off anyway.
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 some kind of NE swell from the early stages, tending E’ly 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 Northern NSW coasts over the next few days, as they’ll see strong cyclone-derived swell regardless. But the variations in surf potential for Southern NSW is non-insignificant: large, or small. Sure, the EC solution whereby we see little cyclone swell may be supplemented by (eventually) some unrelated SE swell from a short wave trough moving into the south-eastern Tasman Sea. But forecasting this is no better than rolling a dice right now.
So, instead of elaborating any further, let’s take another pass on Wednesday.
I’ll also update in the comments below tomorrow if anything new comes to light. But for the meantime: the chances of a signifiant NE tending E’ly swell (and then a large follow up SE swell) from TC Oma is on hold.