UPDATED: Phenomenal NE Swell Potential For The East Coast

30 May 2016 1 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH | Forecaster Blog

(2pm, Thursday 2 June 2016) SEE UPDATED SWELL ANALYSIS & BREAKDOWN HERE

Updated 10.00am Tuesday, 31 May 2016. By Ben Macartney.

The prospect of a big NE swell is now a virtual certainty for the East Coast during the first week of June

The key EC and GFS models remain in close agreement on the early stages of this episode; indicating a steep building trend in NE swell will set in throughout the weekend and probably come to a head late Sunday/ early Monday. These impending developments follow an upper-level trough amplifying over the south-eastern interior on Friday – in turn inducing a major surface trough over inland NSW. As the trough approaches the NSW coast from the west on Saturday it’s set to steadily deepen, forming one or several embedded lows along its length. As the trough approaches the coastal fringe it’s forecast to establish a strengthening NE fetch over the Tasman Sea, forming in conjunction with a broad subtropical ridge over the Tasman Sea.

SEE ALSO: The Wrap Up Of This Weekend's Wonderful & Wild Waves

Over the last 24 hours, the computer models have come back down to earth compared to earlier runs – but it’s still shaping up a seriously large episode none the less. Both GFS and EC runs have also pushed back the timing of the fetch development by about 12 hours. Associated wind strengths are still projected to ramp up steadily throughout the weekend;, strengthening from 15 to 25 knots on Saturday morning, to 25 to 35 knots by Saturday night before reaching maximum speeds of 30 to 40 knots early on Sunday. Given the fetch sets up within close range of the NSW coast, associated wave-potential remains impressive, to say the least. If these projections holds true, we can expect a steep-rising NE swell, building to 3 to 5ft levels on Saturday afternoon before hitting the 5 to 8ft plus across the region on Sunday.

Sunday’s leading pulse is likely to arrive from an acute NE direction of about 50 degrees – so expect plenty of variance in surf heights depending on each breaks exposure. As the fetch contracts further offshore during Sunday and Monday it effectively establishes new pulses of NE and ENE swell that are set to gradually scale down in size over the course of next week.

At this stage, there are good indications Monday will see the largest NE pulse arriving out of the 60-degree band. This is likely to see better organised, mid-period energy peaks in the 6 to 8ft plus range, but this will become clearer as the week progresses. From there, swell direction will start to come around to the ENE as the swell starts to scale down – roughly going from 70 degrees on Tuesday and possibly 80 degrees by Wednesday.

We’re still anticipating stormy conditions as short-period NE swell rapidly builds throughout Saturday – potentially under strong NNE winds. However, during Sunday and Monday conditions are set to transform. Light offshore WNW winds are still likely to prevail as the trough moves offshore on Sunday, but this may be revised depending on how the trough and embedded lows manifest. Monday holds better chances for freshening WSW winds greeting the height of this episode as the offshore trough acts as an effective barrier between the NE fetch feeding into its eastern sector, while facilitating lighter westerly quarter winds across its western side.

From there, we’re likely to see ENE gradually scaling down to more accessible levels from Tuesday onwards as winds begin to shift to the SW. Again, at this early stage there’s still scope for fine tuning to this scenario, to stay tuned for updates as the week progresses.

If you thought conditions have been good of late, just wait until Sunday 5 and Monday 6 June. Photo: CW user 1 to 9.

If you thought conditions have been good of late, just wait until Sunday 5 and Monday 6 June. Photo: CW user 1 to 9.

Initial Report Issued Monday 30 May, 2016

As mentioned late last week, the EC and GFS models have been consistently hinting at the evolution of a significant swell event for our region during the first week of June – and over the last few days these computer models have started falling into strong agreement. These developments are linked to the formation of an upper level low and associated surface trough over the eastern interior late this week. As this extensive surface trough approaches the East Coast from the west on Friday and Saturday it’s set to deepen dramatically, forming one or several embedded lows along its length. As this occurs, the trough sets up a strengthening NE infeed in conjunction with a broad subtropical ridge over the Tasman Sea.

Although all the computer models are in fairly close agreement, there’s still some divergence lending uncertainty to the precise scale and timing of this episode. As of Monday morning, latest GFS model runs paint the most radical picture; depicting the rapid development of a broad NE fetch, strengthening from modest speeds of 15 to 20 knots on Friday night, to 20 to 30 knots by Saturday morning before reaching maximum speeds of 30 to 40 knots or more on Saturday evening and maintaining these thresholds throughout Sunday and early Monday. Given this fetch sets up within point-blank range of the southern half of the NSW coast, associated wave-potential is nothing short of phenomenal. If this scenario proves accurate, it will fuel a steep rising NE swell, building to reaching deepwater peaks of 20 to 25ft off Sydney and the South Coast on Sunday afternoon.

The Wave Tracker depicts significant wave heights of 20 to 25ft immediately off the southern half of the NSW coast on Sunday. This reflects latest, radical GFS model runs capturing a deep surface trough with embedded lows moving off the coast this weekend.

The Wave Tracker depicts significant wave heights of 20 to 25ft immediately off the southern half of the NSW coast on Sunday. This reflects latest, radical GFS model runs capturing a deep surface trough with embedded lows moving off the coast this weekend.

While this points to a phenomenal round of NE swell peaking anywhere from 8 to 12ft plus across exposed beaches, there’s still enough divergence in the modelling to lend uncertainty to this scenario. Although latest EC and ACCESS model runs both reflect these developments, they also draw the NE fetch fairly rapidly away to the east, deeper into the Tasman Sea throughout Sunday. If this proves correct, then we’re more likely to see a large, but not phenomenal peak reaching 6 to 8ft plus across exposed beaches on Sunday.

SEE ALSO: Newcastle On The Pump On Saturday

However this unfolds, we’re also likely we’ll see strong NE winds initially making for stormy conditions as short-period NE swell rapidly builds throughout Saturday. However, by Sunday morning conditions are set to transform as light offshore WNW winds greeting the height of this episode. This ideal scenario is put in place by the continued eastward movement of the surface trough just over – or immediately off the coast on Saturday evening. The trough would act as an effective barrier between the NE gales feeding into its eastern sector, while lighter westerly quarter winds feed into its western side.

So, while this event may not be characterised by a classic East Coast Low setting up offshore, the surface trough may actually facilitate better surface conditions throughout its lifecycle – instead of working around the strong onshore winds often prevalent during the early stages of an ECL.

Latest ECMWF model runs depict the 30 to 40kt NE fetch feeding into the trough's eastern side, while light offshore winds prevail across the coastal fringe. Note, the EC model moves the fetch fairly swiftly offshore - and this suggests the phenomenal wave heights currently projected may come back down to earth over the next few days. Source: BOM.

Latest ECMWF model runs depict the 30 to 40kt NE fetch feeding into the trough's eastern side, while light offshore winds prevail across the coastal fringe. Note, the EC model moves the fetch fairly swiftly offshore - and this suggests the phenomenal wave heights currently projected may come back down to earth over the next few days. Source: BOM.

For now, there’s pretty good consensus among the models surveyed on this scenario; indicating light offshore winds will prevail as the NE swell reaches a peak – probably during Sunday afternoon – but potentially early on Monday. Again, at this early stage there’s still scope for fine tuning to this scenario, to stay tuned for updates as the week progresses.

Latest MSLP forecasts for Sunday depict the broader swell-source: characterised by a deep surface trough interacting with a large high over NZ. Source: BOM.

Latest MSLP forecasts for Sunday depict the broader swell-source: characterised by a deep surface trough interacting with a large high over NZ. Source: BOM.

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