Forecaster Blog: Large NE swell Hits Wednesday But Will It be Good?

5 Dec 2017 2 Share

Ben Macartney

Chief Surf Forecaster

Issued Tuesday, 5 December 2017

Looking at Tuesday’s solid, windblown S swell, it’s hard to imagine solid NE lines stacking up under light offshore winds on Wednesday morning. Never the less, that’s exactly what the charts – including mine- would have you believe. The swell arises from a strong, 20 to 35kt NE fetch now located within close range (give or take 100 nautical miles) of the NSW coast. The fetch is generated by a broad surface trough extending north to south, parallel to the NSW coast and an adjacent ridge to the east.

Is the surf about to tranform into ruler-edged NE perfection on Wednesday morning? Probably not quite, but it ain't looking bad either. Photo: Terry McKenna.

Is the surf about to tranform into ruler-edged NE perfection on Wednesday morning? Probably not quite, but it ain't looking bad either. Photo: Terry McKenna.

As the fetch is aimed more squarely at Bass Strait and Tasmania, most of the NSW coast will be receiving refracted ENE swell spreading angularly off the primary wave-field – and going on latest virtual buoy readings it’s looking sizeable; showing offshore readings of 10ft plus at 9 to 10 seconds; which in theory would have you thinking solid surf ranging anywhere from 5 to 8ft plus.

However, these close range trough/ ridge systems can defy computer-modelled capabilities. The multiple low-pressure circulations lying along the trough means the fetch length is fractured and roughly cleft into two primary areas. It’s only going to set up for a relatively short period before it contracts south-east and further offshore early on Wednesday. These factors - along with an absence of satellite confirmation of the fetch, lend weight to a somewhat more accessible swell-event, speculatively peaking in the 4 to 6ft range across the more exposed breaks, while amounting to 3 to 5ft along less-exposed beaches.

The latest MSLP chart shows the trough running parallel to the coast and the pressure gradient to its east. Source: BOM.

The latest MSLP chart shows the trough running parallel to the coast and the pressure gradient to its east. Source: BOM.

On the upside, the favourable offshore location of the fetch will see a slightly higher period than last weekend’s episode and will also arrive from a slightly more easterly angle of 50 to 60 degrees, compared to last weekend’s more acute, 40 to 50 degree episode. And local winds are looking good; swinging from SSW pre-dawn to WSW by first light – and then going lighter WNW during the afternoon.

Latest Wave Tracker runs show maximum significant wave heights offshore on Wednesday morning. A strong pulse of ENE swell spreading radially off the wave-field will see solid surf on tap across the southern half of the NSW coast throughout Wednesday

Latest Wave Tracker runs show maximum significant wave heights offshore on Wednesday morning. A strong pulse of ENE swell spreading radially off the wave-field will see solid surf on tap across the southern half of the NSW coast throughout Wednesday

Still, there are some other elements that are likely to detract from wave quality. As I write this, SSW winds have kicked to 20 to 30 knots with stronger gusts – and that will mean wobbly conditions early, gradually improving as leftover S swell and sea-state is ironed out by the offshore winds. The other factor to keep in mind is a big tidal range; hitting a high of 2 metres at 10.30am before running out to al low of 0.14 metres at 5.45pm. That will mean a lot of water movement, making for rippy, challenging conditions for most of the day – so it may not be as picture perfect as we might be hoping for. Lets see what the morning brings.

Latest virtual buoy runs look impressive; showing solid ENE swell arriving at 10ft @ 9 to 10 seconds. Sure looks good in theory.

Latest virtual buoy runs look impressive; showing solid ENE swell arriving at 10ft @ 9 to 10 seconds. Sure looks good in theory.


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

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