Blast Off Surf Forecast issued 2.30pm, Tuesday, 15 September 2015. By Coastalwatch Chief Forecaster Ben Macartney.
ESE swell. Around 2ft+, potentially picking up during the day. Grading smaller across open beaches. WIND: Early WSW 10 to 15 knots tending S to SSE during the afternoon.
Mid period ESE groundswell. Possibly undersized at 2 – 4ft early, picking up to 3 – 5ft during the morning, possibly bigger during the day. WIND: Early SW 10 to 20 knots tending S during the afternoon.
Mid period ESE groundswell mixing with S windswell. Around 3 – 5ft, speculatively building during the day. WIND: SSW 5 to 15 knots tending SE during the afternoon.
Steep rising SSE swell and underlying ESE swell. Speculatively 5 – 8ft. WIND: SSW to SSE 15 to 25 knots.
In contrast to previous years there’s an abundance of swell on the horizon for Blast Off this year.
Monday 21st is shaping up as the first of several days of SE to ESE swell for the region and going on recent model runs we’re looking at good to excellent conditions across the region early to mid next week. The eastward extension of a Tasman high coupled with the development of a small low pressure system just west of New Zealand’s South Island on Saturday is projected to support a slow moving SE fetch over the region. This should see primary swell direction turning to the southeast into Sunday and Monday – albeit at relatively low 2ft plus levels on both days.
However, the forecast development of a new low pressure system above the North Island on Sunday presents a case for a better quality ESE swell on Tuesday and Wednesday. The low gives rise to a gale force ESE fetch elongating westward off the North Island and going on latest GFS runs the fetch will remain intact for about 48 hours; driving maximum significant wave heights to peaks of 15 to 20ft over the eastern Tasman Sea. This source is ideally placed to deliver a powerful round of mid period ESE groundswell. Going on current guidance this should fill in early on Tuesday morning, producing a steep rise in surf heights from 2 to 4ft early to a stronger 3 to 5ft or more during the day and plenty more to come on Wednesday. Given this system is yet to develop there’s still ample scope for changes to the projected size and timing of this episode – so stay tuned for updates.
Regardless of how Tuesday and Wednesday’s ESE swell pans out, the longer-term outlook for mid to late next week holds a truckload of new swell potential for the region. Although the outlook surrounding this time frame is plagued by model divergence, there are solid indications we’ll see a new swell-event of S or SSE origins unfolding across the region. Latest GFS model runs pick up a new low pressure system consolidating over the southern Tasman Sea on Wednesday; setting up a broad SSE fetch in conjunction with a new high pressure system building in across Tasmania. The low is loosely projected to track north into the central Tasman Sea on Thursday – thereby dragging the swell-producing fetch closer to the NSW coast as it goes. This would drive a strong building trend in SSE swell; speculatively peaking across northern NSW on Thursday at solid, albeit wind-blown 4 to 6ft levels.
Latest NAVGEM runs exacerbate the strength of the low; suggesting a much deeper low pressure system will power northward, past Tasmania and into the southern Tasman Sea to generate a much heavier spike in S swell over this time frame; speculatively peaking in the 6 to 8ft range across northern NSW on Friday. Finally, recent EC model runs also corroborate these developments; indicating a deep low will form over the south-central Tasman Sea on Tuesday and Wednesday; setting up a similarly heavy push in SSE swell during Thursday 24 September. The upshot of all this is a high probability of a large SSE swell event unfolding mid to late next week, but at this early stage there’s still plenty of scope for revisions to the outlook. This will become clearer as the week progresses.