Forecaster Blog Updated: Large ENE Swell Kicks in This Weekend

9 Oct 2018 6 Share

Ben Macartney

Chief Surf Forecaster

Issued Tuesday, 9 October 2018

There's now high confidence in a strong round of E/NE swell hammering the Eastern Seaboard over the coming days, but by the same token local conditions are likely to leave many of us wanting.

There's been a gradual shift in the projected synoptic pattern over the last few days; flowing through to a substantial shift in the forecast; specifically surrounding a building trend in east to north-easterly swell over the weekend and early next week.

The biggest change surrounds the projected alignment of a broad high pressure ridge firming up over the Tasman Sea. What was originally looking like a strong N to NE fetch developing over the western Tasman has become acutely meridional in nature: i.e. shifting to a much straighter easterly fetch developing on Saturday, before an ENE to NE bias begins to develop into Sunday and Monday.

 

That aside, the strength of the wind-field is still looking robust; developing maximum strength over the northern Tasman Sea at 20 to 35 knots in response to a deepening coastal trough and weak low moving off the southern Queensland coast this weekend.

There's some seriously good NE swell potential in the forecast for next week. Let's hope it stays that way. Photo: Nathan O'Donell.

There's some seriously good NE swell potential in the forecast for next week. Let's hope it stays that way. Photo: Nathan O'Donell.

The primary synoptic driver is a strong, quasi-stationary high pressure system forecast to set up over the southern Tasman Sea  this weekend. As the high extends a broad ridge to the Eastern Seaboard we’re likely to see a deepening surface trough extending over southeastern Queensland and across the northern Tasman. The end result is a broad, slow moving east to north-easterly fetch situated within immediate proximity of the coastline, setting up a strong rise in E/ NE swell for the region early next week.

A large, slow moving high setting up over the southern Tasman this weekend supports major ENE swell-potential for the Eastern Seaboard early to mid next week. Source: BOM.

A large, slow moving high setting up over the southern Tasman this weekend supports major ENE swell-potential for the Eastern Seaboard early to mid next week. Source: BOM.

For Sydney and the South Coast
Although offshore wind-speeds adjacent to Sydney and the South Coast will be weaker, the fetch sets up within immediate proximity of the coast – and hence the resulting ENE swell spreading down the coast is looking substantial indeed; probably reaching a chunky 4 to 6ft across Sydney’s exposed beaches later on Monday and holding similar size early on Tuesday.

The other key factor now detracting from surf-potential is a stronger ENE to NE wind-bias effecting local conditions. That’s likely to mean even sheltered northern corners and south-facing areas will be wind-affected through the peak of this event. At this stage there are indications we’ll see improving conditions from Wednesday onwards; initially as winds turn northerly inshore on Wednesday morning, with scope for lighter NW winds grooming the tail end of the NE swell early on Thursday – but this may well be revised come Monday morning.

Based on latest GFS model runs we could be looking at sizeable and consistent NE swell across the coast early/mid next week. Source Wave Tracker.

Based on latest GFS model runs we could be looking at sizeable and consistent NE swell across the coast early/mid next week. Source Wave Tracker.

The prospect of light offshore winds on Tuesday should have you sitting up and paying attention. Source: BOM.

The prospect of light offshore winds on Tuesday should have you sitting up and paying attention. Source: BOM.

Recent GFS modelling picks up a new mid-latitude low driving across Tasmania extending lighter NNW to WNW winds across the coast from Sydney south on Tuesday – and this is again likely to coincide with still energetic and better orgainised NE swell in the 9 to 11 second band all day, with scope for still good sized surf likely on Wednesday under lighter westerlies.

For southern QLD and northern NSW, this is looks like manifesting a large and unruly easterly swell; fuelled by a robust 30 to 35kt fetch setting up within close range of the coast this weekend. For now this points to heavy surf under easterly quarter winds, building steeply over the weekend and peaking in the 6 to 8ft plus realm on Monday. Although forecast winds aren’t looking as good as locations further south, there’s still plenty of scope for changes as the week progresses

While it’s still a little early to be calling these developments with certainty, the models are in good agreement on the broader synoptic pattern – so confidence on a run of NE swell is medium to high. Stay tuned for updates later in the week.

For southern QLD and northern NSW, the outlook implies large E swell under onshore winds. Source: Wave Tracker.

For southern QLD and northern NSW, the outlook implies large E swell under onshore winds. Source: Wave Tracker.

For now corresponding virtual buoy readings show a peak on Sunday, followed by a slow decline early to mid next week. This may well change as the models get a better handle on the forecast later in the week.

For now corresponding virtual buoy readings show a peak on Sunday, followed by a slow decline early to mid next week. This may well change as the models get a better handle on the forecast later in the week.

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