Swell Alert: Deep East Coast Low to Deliver Another Hiding to the NSW Coast

23 Jul 2020 0 Share

Ben Macartney

Chief Surf Forecaster

Following the exceptionally large and consistent run of SSE, SE and ESE swell that impacted the entire East Coast throughout the week of Monday July 13, you’d be forgiven for thinking the heaviest swell events of the 2020 winter have come and gone. You’d also be wrong.


A deep ECL points to a repeat performance, featuring heavy east swell and strong SSW winds looks like early next week. Photo: cgaborit via the Coastalwatch User Photo Gallery

A deep ECL points to a repeat performance, featuring heavy east swell and strong SSW winds looks like early next week. Photo: cgaborit via the Coastalwatch User Photo Gallery

A deep upper level low and associated surface trough moving across the Eastern States on Friday and Saturday is now widely forecast to induce a deep East Coast Low; initially forming just east of the NSW/ Queensland border on Sunday, prior to rapidly intensifying and tracking south on Sunday.

Largest surf potentially confined to mid-southern NSW coasts: Over the last day or two the key models have converged on these early-stage developments – and that’s now lending high confidence to yet another large to heavy swell event, primarily impacting the mid to southern half of the NSW coast early to mid-next week.

The early stages of the low's development feature a strengthening NE/ENE fetch offshore on Sunday. Source: BOM.

The early stages of the low's development feature a strengthening NE/ENE fetch offshore on Sunday. Source: BOM.

Initial building trend in ENE swell sets in on Sunday: Unlike last week’s storm, the initial fetch-area develops in conjunction with a large, slow-moving high-pressure system located over the south-eastern Tasman Sea (high pressure was located southwest of last week’s low). That initially sees a broadening 30 knot NE/ENE fetch developing across the high’s the north-western flank on Sunday, strengthening to 30 to 40 knots as the low drifts slowly south, becoming centred somewhere off the Seal Rocks to Sydney stretch on Monday.

Large to heavy round of combined NE/East swell and strong SSW, Southerly winds possible on Monday: While there’s still some fine differences among the key models surrounding the alignment and strength of the developing fetch, it presents high confidence for a very large to heavy pulse of NE swell peaking Monday, with a steady transition in swell-direction to the ENE/East occurring throughout the day. Further, the swell would arrive under strong to near gale force SSW winds; potentially gusting up to 30 to 40 knots as the low continues on its poleward track; passing within 200 nautical miles of the Newcastle to Sydney stretch on Monday.

An initial building trend in NE/ENE swell on Monday holds great potential for the region if winds cooperate. Source: Wave Tracker.

An initial building trend in NE/ENE swell on Monday holds great potential for the region if winds cooperate. Source: Wave Tracker.

When it comes to Monday’s forecast size, recent WW3 runs appear to be lagging. Given the forecast location, strength and duration of the developing fetch, ENE swell looks like ramping up steeply; perhaps around 4 to 6ft+ early on Monday towards 6 to 8ft+ during the day - potentially on to peaks of 8 to 10ft+ or more in the afternoon – whether or not it will hit this calibre isn’t set in stone. These specifics are likely to shift as the models continue to nail down the low’s lifecycle over the next couple of days, so stay tuned for updates on Friday.

A stronger ESE fetch potentially develops across the low's southern flank early next week, setting up a similarly large or larger ESE swell for Tuesday/ Wednesday.. Source: BOM.

A stronger ESE fetch potentially develops across the low's southern flank early next week, setting up a similarly large or larger ESE swell for Tuesday/ Wednesday.. Source: BOM.

Range of swell possibilities on the cards for Tuesday and Wednesday: As the low matures and drifts a little offshore on Monday and Tuesday, we may see a strengthening south to SSE fetch developing across its south and southwestern flanks as the initial NE/ENE fetch displaced eastward.

Corresponding WW3 runs have projected seas and swell in the 20ft realm on Tuesday. Source: Surfline.

Corresponding WW3 runs have projected seas and swell in the 20ft realm on Tuesday. Source: Surfline.

However, widening divergence in model guidance opening up a range of surf related possibilities. Recent GFS modelling favouring a still robust SE to easterly fetch briefly setting up across the low’s southern flank on Monday and Tuesday. Hence, the common factor is scope for a very large secondary pulse of ESE or South/SSE swell; speculatively hammering the southern half of the NSW coast in the 8 to 12ft range. These late-stage developments are likely become clearer over the next few days.

More generally we can expect the low’s lifecycle to be much shorter than last week’s Tasman low. As the adjacent high over the eastern Tasman Sea moves across NZ on Tuesday and Wednesday, the low is widely projected to rapidly weaken out. That points to a short tail-end to the swell; quite possibly scaling back to manageable 3 to 5ft levels by Thursday 30th July.

And as if that’s not enough swell-potential for the month of July, there’s yet another Tasman low appearing on latest long-range model runs, hinting at a broad easterly dip setting up across the central-northern Tasman Sea into the final days of July and first days of August.

Tags: Swell Alert , Ben Macartney , topnews (create Alert from these tags)

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