Forecaster Blog: The East Coast’s Tropical Swell Window is About to Wake Up

9 Dec 2020 0

Ben Macartney

Chief Surf Forecaster

You might have been wondering what’s happened the 2020 La Nina and indeed, what all the fuss is about. In previous blogs I pointed to the favourable predisposition towards east-swell that often manifests off the back of a La Nina event. Yet since November we’ve seen pretty typical early summer conditions: mostly featuring a consistent run of small to mid-sized south and SSE swells, punctuated by a few days of NE windswell.

That’s in part linked to early summer pattern, featuring heat-waves across the north of the continent - and we’ve also seen a temporary lull in La Nina conditions, keeping a lid on the kind of easterly swell-potential we might hope to see.

Going on recent model guidance, Christmas comes early to southern Queensland's points. Photo: Mr Vacation.

The tropics awaken at last: That’s all about to come to an end – and in a big way over the coming fortnight. The arrival of an MJO pulse (https://www.coastalwatch.com/surfing/13106/surf-forecast-glossary#m) across the Maritime Continent (currently over Indonesian longitudes) heralds the rapid onset of tropical activity, primarily influencing the western half of the continent – but also over the Coral Sea.

The convective signature of a trough extending off the Queensland coast is a precursor to an energetic easterly swell developing this weekend. Source: BOM

Southern Queensland and far northern NSW cop a hiding, lighting up the points and bays on Sunday and Monday: A developing trough and embedded low are now widely projected to deepen and move within close proximity of (or directly over) the southern Queensland and far northern NSW coast this weekend. Based on tightening model guidance, that’s likely to see all hell breaking loose as an exponential increase in ESE storm-swell ramps up on Sunday, fuelled by gale force onshore SE to ESE winds developing within point-blank range of the region late Sunday/ early Monday, opening up good to excellent surf potential inside the most sheltered bays and points.

This surface wind forecast for Sunday depicts low end gale-force SE/ESE winds will drive a steep increase in ESE swell across northern NSW and southern Queensland this weekend. Source: BOM.

Largest Surge in easterly swell likely to impact mid-northern NSW coasts: However, based on latest modelling, the strongest easterly fetch south of the trough/ low will be displaced south of the border as the system approaches: its upper boundary situated in line with Byron Bay or Ballina. That points to much larger surf impacting the region, roughly bounded by Yamba and Seal Rocks on Monday, speculatively peaking at a stormy 8-10ft+ before starting to settle down again from Tuesday onwards. The silver lining for locations north would be lighter SW/SSW winds, developing in the wake of the trough/low’s southward movement on Monday.

Surfline's wind-model depicts the lighter SW/SSW winds developing across SE QLD as the trough/low drift further south on Monday. Source: Surfline.

Sydney, Newcastle and the South Coast are next in line: The sheer breadth and strength of the developing fetch looks increasingly likely to deliver similarly large and energetic east to ENE swell to Sydney, Newcastle and the South Coast early next week. That’s currently projected to commence with a steep building trend in east swell throughout Monday, leading in a heavy and consistent 8-10ft peak across the region on Tuesday morning.

Maximum east-swell looks like focussing on mid-northern NSW coasts, with Sydney and surrounds seeing similar energy arriving early next week. Source: Wave Tracker.

That’s likely to see wave energy maxing-out the majority of open areas over this time-frame, with scope for good to epic conditions opening up in the days following. That’s based on a gradual transition in swell direction to the ENE as wave-energy subsides, with scope for lighter winds opening up clean conditions on Tuesday and Wednesday next week. Keep in mind there’s plenty room for changes to the size, timing and local conditions over this period, so stay tuned to the detailed forecast as we iron out the specifics later in the week.

Following close behind next week’s swell there’s also emerging potential for a severe tropical cyclone to form over the southwest Pacific Ocean over the southwest Pacific Ocean, developing between Vanuatu and Fiji this weekend. Recent model runs are now moving the prospective cyclone slowly south to southwest, potentially making a direct hit on New Caledonia, before dropping further southwest and into our prime east-swell window mid to late next week. That may enhance an expansive and slow-moving easterly fetch in conjunction with a subtropical ridge to the south – in turn giving rise to a mid to long-period easterly groundswell for the entire East Coast through the middle of December.

CHECK OUT THE DETAILED LONG-RANGE FORECAST HERE