East Coast Swell Alert: April 28, 2015

28 Apr 2015 0 Share

Ben Macartney

Chief Surf Forecaster

If you reside along the Eastern Seaboard and you have a preference for easterly swell, then the following swell alert might be of some interest. The evolution of a deep surface trough and East Coast Low off the East Coast later this week holds some impressive E swell potential for the vast majority of exposed surf breaks facing the Tasman Sea.

Although local winds are not looking ideal through the height of the swell there are likely to be some fine moments as the ENE swell event unfolds over the weekend and early to mid next week. Photo: Coastalwatch Plus member Frankt.

Although local winds are not looking ideal through the height of the swell there are likely to be some fine moments as the ENE swell event unfolds over the weekend and early to mid next week. Photo: Coastalwatch Plus member Frankt.

  • A low pressure trough developing over the northern NSW and southern Queensland interior on Thursday is forecast to deepen as it moves offshore on Friday.
  • A surface low is likely to develop along the trough as it extends southward along the NSW coast.
  • A large ENE swell event subsequently impacts the entire East Coast from Friday through to early to mid next week.
  • Initially southern Queensland and far northern NSW coasts experience a steep rise in surf heights on Thursday afternoon, building to a stormy 5 to 8ft peak Friday.
  • Large ENE swell should persist at these levels across southern Queensland and far northern NSW as strong onshore ENE winds drop off and swing light WNW on Saturday morning.
  • Large ENE swell then impacts the remainder of the NSW coast over the weekend; peaking across the Mid North Coast on Saturday and across Sydney and the South Coast early Sunday.
  • Initially strong onshore ENE winds are likely to produce stormy conditions across the NSW coast on Friday and Saturday, but should clean up as winds swing SW on Sunday.
  • A slow easing trend in E swell follows across the East Coast early to mid next week.

There are some very surf-conducive developments looming off the NSW coast later this week that now present high chances for a large (but not huge) ENE swell event impacting the entire East Coast this weekend. If you take a look at Tuesday’s MSLP chart you’ll see an intense, blocking high pressure system over the Great Australian Bight extending a broad ridge to the Tasman Sea. This high migrates slowly eastward over the next few days - initially straddling Bass Strait on Wednesday before moving over the southern Tasman Sea on Thursday. Once this occurs the high will reinforce a broad ridge across the northern and central Tasman Sea to produce a moderate, 15 to 20 knots easterly fetch aimed squarely at far northern NSW and southern Queensland coasts.

Southern Queensland and far northern NSW
The easterly fetch then rapidly strengthens in response to a surface trough and low pressure system developing off the northern NSW and southern Queensland coast on Friday, triggering a steep rise in surf heights during Thursday afternoon, followed by a stronger push in mid period ENE swell on Friday and Saturday. Initially a strong easterly airflow is likely to blow out conditions across all locations as the swell builds Thursday/ Friday – and it won’t be until the low moves further south that local conditions will abruptly turn favourable. Recent GFS runs move the low south fairly swiftly and this proves true winds are set to swing light WNW across the region on Saturday morning. EC runs slightly delay the southward movement, indicating winds will turn light and variable to light W during Saturday afternoon.

Sydney and the South Coast
Although there’s still some variances among the key models regarding the timing of the ECL’s development and it’s subsequent movement, there appears little doubt a strengthening ENE fetch will gradually broaden and lengthen across the Tasman Sea as the trough/ ECL intensifies. At this stage there’s still some minor divergence among the key models regarding the timing and movement of the low/ trough. The GFS model develops the system more rapidly, indicating ENE winds will peak around 30 knots east of the trough/ low on Friday morning and then extend south to aim directly at the southern half of the NSW coast during Friday afternoon/ Saturday morning. This scenario moves the low rapidly south, parallel to the NSW coast during Friday and holds potential for a strong rise in ENE swell during Saturday; rising to a solid 4 to 6ft into the afternoon and peaking around the 5 to 6ft plus mark across the more exposed open breaks on Sunday.

However, at this stage the nearshore wind-forecast is far less certain. The precise location and strength of the ECL will be the key determinant of local conditions and for the time being there’s still obvious variances present - both among the key computer models and between consecutive model runs. One scenario has the trough providing a synoptic barrier to the onshore ENE winds – resulting in light and variable conditions – possibly during Saturday and/ or Sunday. Alternatively, the low’s southward track may precipitate a southerly wind regime as the swell peaks on Sunday – speculatively starting our SW before swinging S to SE during the day. These variances should be ironed out later in the week so stay tuned for updates.

As the trough/ low deepens off the North Coast on Friday strong onshore ENE winds are aimed at the entire East Coast. Source: BOM.

As the trough/ low deepens off the North Coast on Friday strong onshore ENE winds are aimed at the entire East Coast. Source: BOM.

This Wave Tracker image depicts significant wave height for the NSW coast on Saturday morning, showing peak size occurring across the Mid North Coast. The swell will travel south to peak across Sydney and the South Coast on Sunday.

This Wave Tracker image depicts significant wave height for the NSW coast on Saturday morning, showing peak size occurring across the Mid North Coast. The swell will travel south to peak across Sydney and the South Coast on Sunday.

However it pans out, the ECL is projected to support a broad ENE fetch encompassing the central and north-eastern Tasman Sea throughout the weekend before the fetch contracts to the Southwest Pacific , east of the 160E parallel on Monday. This more distant swell source should continue to supply the East Coast with a sustained run of solid E swell early to mid next week, with smaller leftovers still likely to be present into Thursday 7 and Friday 8 May.

Latest virtual buoy readings for Sydney show large ENE swell peaking on Sunday under early SW winds.

Latest virtual buoy readings for Sydney show large ENE swell peaking on Sunday under early SW winds.


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