Forecaster Blog: Solid NE swell looming for Newcastle, Sydney and the South Coast

28 Nov 2017 0

Ben Macartney

Chief Surf Forecaster

COASTALWATCH | FORECASTER BLOG

Issued Tuesday, 28 November 2017

What a difference a little tilt in swell-direction makes. Under the influence of the predominant south swell regime many exposed, east facing NSW beaches often see lacklustre, long-shore surf; either manifesting as straight closeouts or otherwise offering marginal wave quality. When swell direction swings to the northeast, these same beaches can transform to produce some of the better quality beach-breaks you’re likely to see anywhere. And that’s exactly what looks like happening along much of the NSW coast this weekend.

Friday marks the beginning of a strong building trend in short-range NE windswell that’s set to come to a head this weekend. Unlike the usual, high-pressure driven NE swell events that tend to top out in the 2 to 3ft plus range, this one receives a low-pressure induced turbo-charge during Friday and Saturday; strong enough to facilitate a significantly larger episode peaking at anywhere from 3 to 6ft depending on each locations exposure. 

Based on some recent model guidance, this image could be a fair representation of conditions from Sydney south on Sunday morning. Photo: Uploaded to CW by Ilikebrownie.

Based on some recent model guidance, this image could be a fair representation of conditions from Sydney south on Sunday morning. Photo: Uploaded to CW by Ilikebrownie.

As of Tuesday morning, tight agreement among the key computer models lends high confidence to the swell forecast – and that leaves local winds as the only variable that raises some uncertainty. Over the next few days we see a static high pressure system over New Zealand maintaining a ridge across the western Tasman Sea. At the same time a broad, complex surface trough moving across the NSW and Victorian interior will gradually approach the southern NSW coast from the west. The pressure gradient being squeezed between these opposing features triggers a strengthening NNE fetch to develop just off the NSW coast; initially setting up at 15 to 20 knots late on Thursday before cranking up to 20 to 30 knots or more from late Friday through Saturday and early Sunday.

This Wave Tracker image depicts surface winds of 20 to 30 knots developing offshore on Friday. A steep rise in short-range NE swell follows this weekend.

This Wave Tracker image depicts surface winds of 20 to 30 knots developing offshore on Friday. A steep rise in short-range NE swell follows this weekend.

The close proximity of the fetch to the coast, coupled with an extended, 3 day duration, facilitates rapid wave-growth throughout the weekend; peaking in the 3 to 4 metre range offshore. Short period NE swell subsequently spreads angularly, down the NSW coast; generating a strong push in surf-heights into the 3 to 5ft range across the most exposed open beaches during Saturday afternoon - and it's now clear it will probably hold this size into Sunday morning. Also keep in mind there’s scope for bigger sets at deep-water locations focussing the swell. Conditions on Saturday are dictated by moderate to strong NNE winds ranging from 10 to 20 knots; invariably limiting the cleanest conditions to northern corners and other breaks offering some shelter from the breeze.

Latest mode guidance shows peak wave-growth occurring late Saturday through early Sunday - and this is a key indicator for pumping NE swell on Sunday morning. Source: Wave Tracker.

Latest mode guidance shows peak wave-growth occurring late Saturday through early Sunday - and this is a key indicator for pumping NE swell on Sunday morning. Source: Wave Tracker.

However, by Sunday morning it looks like conditions be cooking just about everywhere. As the aforementioned surface trough moves offshore a low is forecast to form, somewhere east of Bass Strait or just off the far southern NSW coast. Both the location and movement of the developing low will be a key determinant of wave-quality on Sunday. While some recent model guidance has been picking up a southerly (SSW) change moving up the southern half of the NSW coast as the low develops offshore early on Sunday, the majority of latest runs are now moving the low away to the south-east; thereby facilitating lighter offshore WNW winds across the coast all day. So at this stage it looks like it’s well worth setting some time aside for surf or three on Sunday, but stay tuned for updates to see if this holds true over the next few days.

Latest model runs, like this one from the BOM, depict a lighter WNW airflow moving in over the coast as the fetch contracts eastward on Sunday morning. Fingers crossed this holds true. Source: BOM.

Latest model runs, like this one from the BOM, depict a lighter WNW airflow moving in over the coast as the fetch contracts eastward on Sunday morning. Fingers crossed this holds true. Source: BOM.


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