Forecaster Blog: Major East Coast S swell On The Cards

25 Oct 2017 0 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH | FORECASTER BLOG

Issued Wednesday, 25 October 2017

Late spring can be a pretty lacklustre time of year for surfing across the Eastern Seaboard and the past week has been pretty typical; characterised by small-scale S swell crossing over with localised NE windswell. This absence of notable swell belies latent potential for major swell event at anytime of year – and by the looks of the forecast for next week we could see a return of winter-like conditions as a deep low sets up over the Tasman Sea. For now these prospective developments are still days away – and that means there’s ample potential for big shifts in the outlook – but going on latest model runs it’s fair to say we could be looking at some radical developments over the course of next week.

A major S to SE swell event could eventuate mid to late next week. Stay tuned to how this will unfold as the week progresses. Photo: Uploaded by Dkimber.

A major S to SE swell event could eventuate mid to late next week. Stay tuned to how this will unfold as the week progresses. Photo: Uploaded by Dkimber.

Over the past few days EC model runs have been consistently picking up the formation of an intense mid-latitude low over the Tasman Sea – and it’s only now that corresponding GFS runs are starting to reflect the same possibility. This activity commences with a vigorous frontal progression sweeping across Tasmania and Bass Strait on Sunday and out into the south-west Tasman Sea on Monday. Initially this should see a vigorous, short-range southerly fetch developing along the southern half of the NSW coast, driving a steep rise in S windswell throughout the day. For now the models vary on the timing of the change and associated building trend – but either way, it points to plenty of S windswell in the water across the southern half of the NSW coast on Tuesday; speculatively running at a consistent 3 to 4ft plus across southern exposures.

However, it’s the subsequent development of a low pressure system over the southern Tasman Sea on Tuesday that holds major surf potential for the region. EC runs steadily intensify the low roughly 450 nautical miles east of Batemans Bay; initially producing a broadening and further strengthening of the southerly fetch across its western flank. The low is then projected to further intensify as it retrogrades (moves westward) back towards the South Coast on Wednesday – and it’s this stage that may prove to be the catalyst for an extra-large S swell later next week.

The Wave Tracker, driven by the GFS model, shows a large, but not off the charts S swell event taking shape mid-next week. Some alternative guidance suggests we could be looking at something much bigger.

The Wave Tracker, driven by the GFS model, shows a large, but not off the charts S swell event taking shape mid-next week. Some alternative guidance suggests we could be looking at something much bigger.

A sustained period of 30 to 40kt southerly gales supported by the low could drive S swell into the 6 to 12 realm during Wednesday and early Thursday – but at this stage there’s little certainty on the particulars. While corresponding GFS runs also intensify the low on Tuesday, the fetch remains further offshore and propagates northward as the low moves parallel to the NSW coast to become centred off the northern NSW coast on Wednesday. For now this points to a still large, but not heavy S swell – so the upshot is increasing confidence for some kind of significant S swell mid to late next week. Going on GFS, there’s also some latent potential for a secondary round of E swell linked to the low; speculatively arriving over the weekend of Saturday 4th November. This will become clearer as the week prorgresses so stay tuned for updates.



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