Forecaster Blog: Large NE swell To Grace The NSW Coast And TC Owen To Follow
Issued Tuesday, December 11, 2018
Christmas arrives early for surfers along the NSW coast this year. There’s now high confidence surrounding the onset of an energetic and long-enduring run of NE swell setting the region; developing in response to a surface trough and low pressure system deepening over the south-eastern interior later this week. As of Tuesday morning, the key models are showing tighter agreement on this emerging pattern; indicating a long NNE fetch will set up immediately offshore as the low interacts with a high moving across the far southern Tasman Sea.
This event gets underway across most of the NSW coast during Thursday; initially manifesting as a fairly lackluster increase in NE windswell ranging from a junky 1 to 3ft along open beaches. However, this should prove to be a precursor to a more significant increase in short-period NE swell; building steeply on Friday before coming to a head this weekend.
Given the close-range of the NNE fetch to the coast, it’s clear that locations from Sydney south will be the primary beneficiaries with respect to size and power – but having said that, mid and northern NSW regions will also benefit from a sustained run of mid-sized NE windswell, exhibiting lower heights and periods the further north you go.
With peak wind-strength forecast at 20 to 35 knots, this event is shaping up as a thumping, short-period NE swell, prospectively peaking in the 4 to 8ft range at NE swell-magnets this weekend. To elaborate on this, we’re likely to see a wide-range of surf-heights resulting from the acute north-easterly direction and relatively short peak wave-periods of 8 to 9 seconds. So while you might see consistent 3 to 4ft sets at one beach, the one around the corner could be more like 4 to 6ft plus – and deeper water reefs holding the swell bigger again.
Having said that, there’s still scope for some downgrading to these estimates. While it’s clear the emerging synoptic pattern presents high chances of a long-enduring NE swell event, there’s still a fair chance we’ll see continued fluctuations in projected wave-height. The key variable is the location of the fetch, coupled with its strength, duration and orientation to the coast. Previously all these factors had been varying with each new model run, depending on where the low sets up and which way it moves across the south-eastern interior – but as of Tuesday morning all the signs are looking good.
As for local conditions, it’s clear we’re looking at a persistent north to north-easterly wind-regime, mostly favouring sheltered northern corners and those stretches that tilt a little to the south. However, there’s also good indications the pressure gradient will remain fairly weak along the coastal fringe, opening the door to lighter north or even offshore NNW to NW winds both on Saturday and Sunday mornings – this will become clearer later in the week.
The other, potentially big development now showing up on the major models is the re-birth of Tropical Cyclone Owen. The storm is now re-intensifying over the Gulf of Carpentaria and it’s loosely projected to move southeastward to the central-northern Queensland coast before tracing it southeast this weekend. Both EC and GFS runs are now showing loose agreement on a continued south-eastward track with intensification early next week; a scenario that would culminate in a significant tropical cyclone forming within close proximity of Frazer Island and the southern Queensland coast.
However, once the storm moves offshore, the models begin to diverge. Overall, latest model guidance is currently playing down its size and strength; indicating it may manifest as a relatively small-scale feature exerting a relatively localised influence on SE Queensland and far northern NSW. Still, there are other scenarios that keep TC Owen on a east to south-east track that would take it deeper into the northern Tasman Sea; thereby exposing the NSW coast to a compact easterly fetch wrapping around its southern quadrant. At this early stage we’ll just have to sit tight and see whether or not this comes to fruition, so stay tuned for updates over the course of the week.
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