Forecaster Blog: Weekend NE swell Just the First of Two Large Pulses for the NSW coast

1 Dec 2017 0 Share

Ben Macartney

Chief Surf Forecaster

Issued Friday, 1 December, 2017

The first week of summer isn’t exactly renowned for pumping surf, but the current, freakish weather pattern now taking shape over eastern Australia promises an absolute NE swell-fest along the NSW coast. Over the last 48 hours we’ve seen the forecast continuing to firm up for this weekend. On top of that, there’s some additional developments shaping up into the longer-term and it’s now clear that this weekend’s NE swell event is just the first of two, strong pulses; with a second round of energetic NE swell arriving next week now looking both larger and more powerful than this weekend’s event.

This looks like it's going to be a common sight along the NSW coast throughout the first week of December. Photo: Jarrod Slatter.

This looks like it's going to be a common sight along the NSW coast throughout the first week of December. Photo: Jarrod Slatter.

First NE pulse to peak late Saturday through early Sunday
As mentioned in an earlier blog, Friday marks the beginning of a strong building trend in short-range NE windswell that’s set to peak across the southern half of the NSW coast this weekend; probably showing peak size late on Saturday and holding at similar levels early on Sunday. 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; strong enough to support a slow-moving 20 to 35kt NNE fetch immediately offshore for an extended period. The end result is a significant rise in NE swell; peaking in the 3 to 5ft plus range, with size depending on exposure.

Latest Wave Tracker runs depict the NE swell offshore, spreading down the southern half of the NSW coast on Sunday.

Latest Wave Tracker runs depict the NE swell offshore, spreading down the southern half of the NSW coast on Sunday.

Wednesday’s model runs remain in close agreement; thereby lending high confidence to the forecast. The good news is the outlook for local conditions have also firmed up. It’s now clear that we’re looking at a favourable NW bias in local winds on Sunday morning and are firm indications they’ll remain light offshore all afternoon. It’s also now clear there will be plenty of NE swell leftover on Monday; probably ranging from 3 to 4ft under light offshore or fluky SW to SE winds early before easing a foot during the day. This is now also set to combine with an additional – and possibly larger mid-period S swell; arising from the aforementioned low as it drifts away to the southeast and intensifies off Tasmania on Sunday.

This BOM chart displays forecast signficant wave height offshore on Sunday. Friday morning's model runs have abruptly shifted on S swell potential arising from the low as it intensifies of Tassie; indicating we'll see a strong S pulse on Monday superseding the easing NE swell. Source: BOM.

This BOM chart displays forecast signficant wave height offshore on Sunday. Friday morning's model runs have abruptly shifted on S swell potential arising from the low as it intensifies of Tassie; indicating we'll see a strong S pulse on Monday superseding the easing NE swell. Source: BOM.

Second NE pulse speculatively builds Tuesday, peaks Wednesday
Just as this event starts to wind down early next week it looks like we’ll see a renewed deepening of the surface trough as it remains slow moving, just west of the north-eastern coastal-fringe on Monday. This is loosely projected to induce one or two embedded lows as the trough moves offshore on Tuesday, with some recent model runs favouring a primary cell developing somewhere off the mid to northern NSW coast late Monday/ early Tuesday.

A renewed strengthening of the NE fetch offshore follows throughout Tuesday; facilitating rapid wave-growth as it capitalises on the still active sea-state present in the wake of this weekend’s event. The models are also starting to show some loose agreement; pushing the low rapidly poleward, parallel to the NSW coast during the day. The net effect would be a broad NE fetch; briefly cranking up to 30 to 35 knots within close-range of the coast on Tuesday, before contracting further offshore and gradually edging out of range of the coast during Wednesday.

CHECK THE DETAILED SYDNEY AND SOUTH COAST FORECAST HERE

The BOM's access model reflects broad model consensus surrounding the development of another strong NE fetch positioned a little further offshore on Tuesday. Source: BOM.

The BOM's access model reflects broad model consensus surrounding the development of another strong NE fetch positioned a little further offshore on Tuesday. Source: BOM.

The upshot is potential for another large run-up in NE swell – at least on par with, but more likely larger than this weekend’s event. The sustained 30kt plus winds and favourable position of the fetch also point to a slightly higher period episode arriving from a slightly more easterly angle of 50 to 60 degrees, compared to this weekend’s more acute, 40 to 50 degree episode. While there’s still plenty of uncertainty on local conditions, recent model runs are starting to lean towards favourable SSW or straighter WSW winds – this will become clearer over the coming days.

FOLLOW THE EVOLUTION OF THE SWELL ON THE WAVE TRACKER

The resulting deepwater NE swell arising from the second system holds excellent NE swell potential for the NSW coast mid-next week.

The resulting deepwater NE swell arising from the second system holds excellent NE swell potential for the NSW coast mid-next week.


Tags: Forecaster , Blog , NE , SWELL , Ben , Macartney (create Alert from these tags)

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