Forecaster Blog: The Next Big East Coast Low Is Looming
COASTALWATCH | Forecaster Blog
Issued Wednesday, 15 June 2016
Just as we begin to count the cost – and the innumerable good waves produced by the monster ENE swell that rocked the Eastern Seaboard last week – yet another one is already beginning to taking shape on recent computer modelled projections.
At first glance the evolution of the system shows an uncanny resemblance to its predecessor; spawning off a deepening upper-level trough migrating across the eastern Australian interior later this week. The system induces a deep surface trough and associated low-pressure system on the cusp of the northern NSW coast over the weekend before it moves offshore on Sunday night.
As the system approaches the coast on Sunday it draws in a strengthening NE fetch throughout the western Tasman Sea; forming in conjunction with a high pressure system setting up over New Zealand. While a steep rise in NE swell follows by Monday morning it’s at this point we can start to differentiate it from last week’s episode.
What’s immediately clear is that the low/trough won’t be generating the same phenomenal wave height or exhibit the same longevity of the last event. Although the NE fetch forming over the Tasman on Sunday and Monday should generate surface wind speeds of 25 to 35 knots within close range of the NSW coast, the low is forecast to move swiftly south along the coastal fringe on Monday. At the same time, the high over New Zealand also moves eastward more rapidly – nor is the high as intense as it’s predecessor.
The upshot is a broad NE fetch of lower strength and duration – in turn translating into a still large, but more accessible NE/ ENE swell – mostly amounting to 4 to 6ft across exposed beaches on Monday, with the more exposed breaks focussing the swell potentially up to 5 to 8ft on the. However, the rapid eastward contraction of the wind-fetch into the central-eastern Tasman Sea during Monday should flow through to a notable drop in size by Tuesday morning; speculatively dropping to a less consistent 3 to 4ft on the larger sets ahead of a further decline during the day. The good news is both Monday and Tuesday are likely to see a favourable, westerly quarter wind regime in place, following the rapid poleward movement of the ECL.
At this early point in time, it’s still difficult to decipher exactly how the later stages in the ECL’s development will impact the coast into the middle of next week. Wednesday morning’s model runs show loose agreement between EC and GFS models, indicating the low will transition into a deep extratropical, cold core system as it collides with a frontal progression off Tasmania’s east coast on Tuesday; speculatively giving rise to a gale force WSW fetch extending out of eastern Bass Strait.
While this holds speculative potential for a secondary round of S groundswell for the NSW coast into Wednesday and Thursday, there are also indications the low will simply drift entirely out of our swell window as it accelerates southward over this time frame – in which case we could be looking at a further decline small/ tiny leftovers by Wednesday 22 June. Having said that, there’s still plenty of scope for changes to this scenario as the models better capture the systems development, so stay tuned for updates as the week progresses.
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