Forecaster Blog: Impending East Coast Low Threatens Storm-Swell For The NSW Coast

7 Jul 2015 1

Ben Macartney

Chief Surf Forecaster

Issued Tuesday July 7, 2015

If the recent spate of light offshore winds, cloudless skies and small to mid sized southerly groundswell lulled you into believing we’re in for a relatively subdued winter surf-season, well prepare to have your expectations readjusted – potentially in spectacular fashion. The mention of an East Coast Low (ECL) usually means there’s some serious surf afoot and while it’s still a little early to be delving into wave height and direction specifics, it’s increasingly looking like we’ll feel the brunt of a large, ECL driven swell event throughout the middle of July. Over the past week long-range computer models have been consistently forming an East Coast Low over the Tasman Sea - albeit in varying locations with each consecutive model run.

Hey, not trying to hype it up or anything, but this is one example of what an ECL can do to the surf across the East Coast. Photo: Coastalwatch.

Hey, not trying to hype it up or anything, but this is one example of what an ECL can do to the surf across the East Coast. Photo: Coastalwatch.

However, over the last 48 hours the models have begun to show some cohesion and are now in loose agreement on the early stages of the ECL’s lifecycle. This presents moderate confidence a low pressure centre will develop just east of Bass Strait on Sunday before intensifying over the southern Tasman Sea on Monday 13 and Tuesday 14 July. However, at this early stage there’s still a big question mark hanging over associated swell potential. The bulk of model runs maintain the core of the system within close proximity of Bass Strait – and this may well inhibit the development of any S or SE wind-fetch inside the NSW coast’s swell window – thereby delaying the onset of any S/SE swell until Wednesday 15 July. Further, the close proximity of wind-fetch to the south-eastern Australian landmass may well dilute surf potential, culminating in a relatively modest S swell event peaking in the 3 to 6ft range. In contrast, several recent model runs capture a gale force S or SE fetch setting up inside our swell window as the low intensifies east of Tasmania/ Bass Strait early next week – and this leans towards a steep run-up in S/SE storm-swell during Tuesday 14 and Wednesday 15 July, potentially peaking in the 6 to 12ft range. 

As of Tuesday afternoon the bulk of model runs are placing the ECL in close proximity of  Bass Strait. This may prove a constraint to swell development of the East Coast. Source: BOM.

As of Tuesday afternoon the bulk of model runs are placing the ECL in close proximity of Bass Strait. This may prove a constraint to swell development of the East Coast. Source: BOM.

The BOM's ACCESS model shows surface wind, depicting a deep belt of SE gales aimed at Tasmania on Monday 13 July. This holds potential for a strong SSE groundswell for the NSW coast mid next week.

The BOM's ACCESS model shows surface wind, depicting a deep belt of SE gales aimed at Tasmania on Monday 13 July. This holds potential for a strong SSE groundswell for the NSW coast mid next week.

Latest Wave Tracker runs pick up a gale force S fetch forming as the low intensifies east of Bass Strait on Monday. A large spike in S swell would follow on Tuesday 14/ Wednesday 15 July.

Latest Wave Tracker runs pick up a gale force S fetch forming as the low intensifies east of Bass Strait on Monday. A large spike in S swell would follow on Tuesday 14/ Wednesday 15 July.

At this early stage it’s probably not worth getting hung-up on the specifics of each model run. Given there’s roughly 100 hours until cyclogenesis commences there’s little doubt we’ll see regular readjustments to the forecast location and strength of the low as the computer models gradually get a better handle on it’s evolution, so stay tuned for updates over the course of the week. 

FOLLOW THE DEVELOPMENT OF THE ECL ON THE WAVETRACKER

Tags: East Coast Low , surf forecast (create Alert from these tags)

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