Forecaster Blog: Wave Periods as Long As You Like along the East Coast
Issued Wednesday, 16 May 2018
It’s not everyday you see peak periods of 20 seconds appearing on virtual buoy data for the NSW coast, but that’s precisely what’s been appearing on recent model runs. More typically found along more distant shores like Indonesia and Fiji, such long intervals often denote the leading edge of a significant long-period groundswell – and that’s exactly what’s inbound along the NSW coast throughout Friday and Saturday.
The source is a compact polar low currently positioned far below Tasmania; roughly 1,670 nautical miles south-southwest of Sydney. The storm has been and is continuing to generate a 40 to 50kt WSW fetch throughout our long-range swell window. Further, the slow westward movement of the storm has carried the fetch along with the swell being generated; thereby compounding maximum significant wave-height below the 50S parallel.
At first glance at a two-dimensional wave chart you’d be forgiven for assuming this source lies too far south and west of the Tasman Sea to impact the NSW coast. In reality, the fetch areas is well placed inside the extremities of our long-range swell window. Groundswell spreading radially off this source will fan out throughout the Pacific basin over the coming week, following the curvature of the Earth to arrive at locations far and wide.
One of its first ports of call is the NSW coast. A powerful pulse of S groundswell follows a Great Circle Path, travelling north through Tasman Sea over the coming days. A subsequent, strong building trend in S groundswell will become evident across Sydney, Newcastle and the South Coast throughout Friday; probably starting out fairly small and inconsistent ahead of a strong push into the afternoon. Keep in mind the extremely high-period and acute directional band (190 to 200 degrees) will result in disparate wave heights; showing notable size in the 3 to 4ft range and possibly bigger across true south facing breaks, while amounting to anything from 1 to 4ft along the majority of open areas depending on exposure.
It looks like the bulk of groundswell will show up across mid and northern NSW coasts at similarly powerful levels on Saturday; again producing widely varying surf depending on an individual locations exposure to the deepwater energy.
If you’re feeling intrepid, you’d be well placed to chase this event as it fills in across Fiji and Raglan in New Zealand over the course of next week. Keep and eye on the Wave Tracker to see how will impact these Pacific locations over the coming days.
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