Forecaster Blog: Deep East Coast Low Wreaks Havoc Next Week

9 Jul 2020 0 Share

Ben Macartney

Chief Surf Forecaster

Issued Thursday, 9 July 2020

In the week’s following the two big winter south swells that hammered the coast back in May and June, we’ve seen an extended run of small to mid-sized swells opening up many days of good to great surfing conditions across the NSW coast. We’ve also started to see sand-banks gradually rebuilding and filling across the deep gutters left in the wake of the swells – but it's now clear the banks are in for another major shake-up next week.

The development of a deep East Coast Low off the NSW coast looms as a near-certainty early to mid next week. The lead-time on its development has left the what’s, how’s and when’s of its associated swell potential shrouded in uncertainty  – but the answers to those questions are now starting to become apparent, with the various forecast models gradually moving towards consensus surrounding the timing of the low’s development and its tenure over the Taman Sea.

There's little doubt it's going to be big next week, but clean options are likely to be limited. Photo: Uploaded to CW by Mattimages.

There's little doubt it's going to be big next week, but clean options are likely to be limited. Photo: Uploaded to CW by Mattimages.

That lends increasing confidence to a steep increase in SSE/SE swell, commencing on Monday afternoon and coming to a head at extra-large to heavy levels throughout Tuesday and Wednesday. We’re now seeing the more reliable models pinpointing the inception of cyclogenesis to somewhere just off the mid-northern to central NSW coast on Monday morning, followed by southward movement and rapid intensification east of the Newcastle to Sydney stretch later Monday through early Tuesday morning.

Some recent model runs also have the low developing a little further north, along the northern NSW coast. Source: BOM

Some recent model runs also have the low developing a little further north, along the northern NSW coast. Source: BOM

For Sydney, Newcastle and the South Coast, opens the door to the possibility of light offshore WSW to SW winds greeting a rising SE swell throughout Monday; potentially opening up excellent conditions as the swell starts to jump up throughout the afternoon. This possibility is given further weight by several recent model runs indicating the low will stall near Jervis Bay; thereby keeping the northern boundary of the developing SE fetch below the 34S/35S parallel. Some of these models suggest these favourable conditions will spill over into Tuesday morning before the low moves north during the day; eventually bringing the strong onshore winds and heavy rain to Sydney and surrounds into Tuesday afternoon.

With the low forecasted somewhere off Sydney, we may see the best of both worlds as SE swell arriving off its southern flank is greeted by light westerlies. Source: BOM.

With the low forecasted somewhere off Sydney, we may see the best of both worlds as SE swell arriving off its southern flank is greeted by light westerlies. Source: BOM.

You might say the outlook from Tuesday onwards isn’t looking quite so encouraging. As the low further intensifies and drifts further eastward early on Tuesday it’s likely to expose the region south of Seal Rocks to near gale force South to SSE winds, whipping in across the storm’s western flank.

That would lead in a steep increase in southerly storm-swell generated by a 35 to 45 knot fetch situated within point-blank range of the coastal boundary; rendering exposed beaches unsurfable on Tuesday morning and limiting options to the most sheltered southern corners and north-facing coasts as the swell steadily builds throughout the day. That’s likely to leave little to be desired as the howling winds drive persistent and possibly heavy rainfall early in the day– mostly focused on the coastline bounded by Wollongong and Newcastle.

Tuesday's initial rise in south/SSE swell looks heavy to say the least. Source: Wave Tracker.

Tuesday's initial rise in south/SSE swell looks heavy to say the least. Source: Wave Tracker.

Compounding Tuesday’s leading spike in South swell is the likelihood of a similarly large and more powerful round of SE/ESE groundswell arriving on Wednesday – again under strong southerly quarter winds remaining in force across the coast throughout the day. This secondary pulse arises from a broad, SE to ESE fetch developing across the low’s southern sector; nurtured by a quasi-stationary, cradling high pressure system to the south.


Given the emerging model consensus, that currently points to monstrous, stormy 10 to 15ft SE swell hammering exposed areas on Wednesday morning, gradually settling and possibly transitioning more ESE in direction - still at considerable size on Thursday. Beyond that, the models shift the fetch to the south-eastern Tasman Sea, off NZ’s west coast – and that hints at a continues run of still large, but far more accessible ESE swell for the region into Friday and the weekend of Saturday 18th.

At this early stage, these specifics are still wide open to revisions, with emerging divergence from Tuesday onwards lending a higher degree of uncertainty to conditions from Wednesday to Friday next week. Stay tuned to the detailed forecast for more details as the system evolves.


Tags: Forecaster Blog , Ben Macartney , East Coast Low , topnews (create Alert from these tags)

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