East Coast Swell Alert: October 14, 2014

14 Oct 2014 0 Share

Ben Macartney

Chief Surf Forecaster

Issued 3.00pm, Tuesday, 14 October 2014.

A deep, complex low centred off the South Coast drives a strong southerly change across Sydney and surrounds on Tuesday afternoon. This is closely followed by a heavy spike in S storm-swell, peaking at 8 to 10ft across south facing breaks on Wednesday.

- A complex low centred off the NSW coast extends a trough northward across Sydney and surrounds during Tuesday afternoon, leading in a vigorous southerly change and steep rising trend in S swell late in the day.

- The change leads in a close range, gale force fetch responsible for a heavy spike in S storm-swell, peaking early Wednesday in the 8ft plus range across Sydney’s south facing beaches, grading smaller elsewhere depending on exposure.

- The localised characteristics of the storm system constrain the primary impact of the storm-swell to locations south of Seal Rocks, with mid to northern NSW locations receiving a smaller pulse ranging from 3 to 6ft depending on exposure.

- The low gradually weakens and moves away to the southeast on Wednesday and Thursday, precipitating a slow easing trend in SSE swell into the end of the week.

The combination of a heavy S swell and SW winds should see some interesting conditions across Sydney and the South Coast on Wednesday. Photo: Randy Sparrow.

The combination of a heavy S swell and SW winds should see some interesting conditions across Sydney and the South Coast on Wednesday. Photo: Randy Sparrow.

OVERVIEW
The southwest Tasman Sea is a frequent meeting point for sub-tropical moisture and cold blasts of air originating from polar latitudes, making it one of the more volatile regions with respect to storm development. This is exactly what’s currently unfolding over the region following the amalgamation of a broad surface trough and vigorous frontal system off the NSW South Coast over the last 24 hours; producing a complex low pressure system exhibiting two centres along the trough line on Tuesday.

Source: BOM. A complex low situated within close proximity to the NSW coast supports a gale force southerly fetch offshore overnight, generating a heavy rise in S swell by Wednesday morning.

Source: BOM. A complex low situated within close proximity to the NSW coast supports a gale force southerly fetch offshore overnight, generating a heavy rise in S swell by Wednesday morning.

As depicted above the low combines with a high pressure system over the Great Australian Bight to form a tightening pressure gradient across its south-western quadrant – in turn generating a gale force SSE fetch situated within close range of the southern half of the NSW coast. As the low intensifies and drifts northward overnight the fetch strengthens as it extends further up the NSW coast, driving a steep rise in SSE swell by Wednesday morning; peaking at a stormy 8 to 10ft across southern exposures while producing wide-ranging surf heights across most locations with size contingent on exposure. The close range of the swell source will also produce a highly energetic sea state characterised by consistently large waves between the sets.

The pressure gradient between the complex low and high to the west also generates a brief period of gale force southerly winds overnight, so if you’re located within a warning area you might want to batten-down the hatches so to speak. As the low begins to drift south-east during the early hours of Wednesday morning winds begin to orient south-west – no doubt making for good, albeit challenging conditions at breaks holding the swell. Further, a predominant southerly bias in swell direction will produce much smaller, more accessible conditions inside the more sheltered southern corners, so it’s well worth a check at these locations if you have the time. SSE swell will ease considerably overnight but there will still be strong, mid to large surf ranging from 4 to 6ft across the region on Thursday under early offshore winds, preceding a further decline to more accessible levels by Friday. 

Source: BOM. This computer modelled depiction of surface winds shows the compact area of southerly gales setting up overnight.

Source: BOM. This computer modelled depiction of surface winds shows the compact area of southerly gales setting up overnight.

This Wave Tracker image shows significant wave heights peaking in the 20ft range offshore early on Wednesday.

This Wave Tracker image shows significant wave heights peaking in the 20ft range offshore early on Wednesday.


Tags: swell alert , storm-swell , East Coast , surf forecast , topnews (create Alert from these tags)

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