Sydney Hunter Illawarra Surf Forecast by Steve Shearer (issued Mon 23th August)

Forecast Summary (tl;dr)

• Small NE windswell  later Mon, holding Tues morning before being swamped by steep rising S swell PM
• Late kick in S’ly swell Tues PM, with stormy S swell Wed as Tasman low winds up E of Sydney
• Strong SSE swell Thurs as Tasman low drifts E into Tasman, slowly easing (but still solid) Fri and into the weekend
• Long range inconsistent E swell in the mix from Thurs-Sat, overshadowed by dominant S/SE swell regime

Recap

A weekend of very small surf just passed with Saturday seeing the best of it-  a small S swell signal that measured up to some 2-3ft surf on the Hunter, grading smaller 1-2ft in Sydney and southwards. By Sun that signal was very weak and barely surfable with only Newcastle seeing some stray 2ft sets. This morning is mostly tiny across central/southern NSW, with a faint but building NE windswell visible. This is a precursor to a developing Tasman low which is going to deliver a very significant swell event. Read on for details.

This week (Aug 23-27)

The weekend's extremely warm, benign weather is about to be swept away by a wintry blast as a trough following the passage of a cold front later today interacts with a cold pool and forms an explosive surface low Tuesday morning. This cut-off Tasman low will generate an over-size local S swell event and dominate our surf and weather for the rest of the week. 

To back up a step, a NE infeed into the trough and developing low is dragging it’s heels- ASCAT passes show a very weak fetch that is likely to increase overnight. That offers a window tomorrow morning for NE sidewinders as pre-frontal N/NW winds blow. It’ll be a brief window, especially on the Illawarra, as the developing low generates a fresh and gusty SW to SSW flow that is expected to rapidly increase. Severe gales to storm force SW to SSW/S winds are forecast later tomorrow and overnight Tues into Wed. 

There’s still some slight difference timing wise between major models and with the system and associated winds so close to the NSW coast this could be significant, even so close to the event. 

EC winds the low up earlier, by 3pm extending severe gales north of Sydney. Proximity equals size and this will lead to a rapid step-ladder increase in size through the  a’noon up into the 6-8ft range through the a’noon.

GFS has a more delayed development allowing a window of smaller S swell through the early-mid afternoon, building from 3-4ft into the 4-6ft range later in the day.

Keep in mind this initial fetch is quite thin and SSW in orientation so despite buoys being massive, inshore wave heights will be a bit down on the hype. To get away from S’ly component winds into more sheltered spots you’ll have to sacrifice size further compromising surfable options.

In short, keep expectations pegged through tomorrow.

The low moves slowly SE on Wed with a proximate fetch hugging the coast of severe gale SSW winds and a better aligned fetch of SSE/SE winds starting to develop along the SW flank of the low. It’s going to be a big, windy day anyway you slice it. How big? Again, with the thin coast-hugging fetch not optimally aligned there’ll be a cap on wave heights, despite wave buoys likely to be maxing. Likely 8ft+, bigger at S facing beaches and grading smaller into more protected spots, where surfing will be feasible. The Illawarra is likely to see bigger 10-12ft storm surf through Wed, as is the Hunter. Strong wind to gale force SW winds are forecast for the day, with a brief window of more W/SW winds possible north of the Harbour.

Thursday looks the day for surf to thicken up as the deeper, better aligned SSE/SE fetch on the SW flank of the low generates strong SSE swell for the Central and Southern NSW Coast. With the low moving away local pressure gradients will ease and lighter SW winds will see a day of cleaner, pumping waves. 

There’ll be a small amount of mid period E swell in the water from the long range E’ly fetch that has been present in the South Pacific since Sun and a trace of long period S swell generated by a passing polar low on Tuesday but both of these swell trains will be dwarfed by the dominant SSE swell from the Tasman low. Expect sets in 8ft+ range through Thursday. Needless to say, experienced surfers only. Even sheltered spots will have some serious water movement happening.

Friday looks great as well. With the low weakening and moving away we’re left with a weak synoptic W’ly flow and strong leftover 5-6ft sets, possibly 6ft+ at exposed magnets, slowly easing through the day. Lully E swell will supply some 3ft sets and these may be more noticeable as the dominant SSE swell eases back in strength. Light offshore winds should tend to light and late seabreezes through the day. It’s a day to get a go out in, if you are able.

Next weekend (Aug 28-29)

We’ll be on a slow roll-off this weekend as the Tasman low lingers in the eastern Tasman Sea with a well consolidated but weakening fetch of SSE winds through the central Tasman.  Winds could be an issue with high pressure moving east of Tasmania setting up a S’ly flow along the NSW coast. I’d say there are good odds for a morning SW breeze before winds tend onshore. Sat should see 4ft sets with some stray, super inconsistent 2-3ft E swell still on the menu, with both sources slowly easing. 

Residual swells from the E and SE on Sun offer plenty of fun 3ft beach break and light morning land breezes promise clean conditions before seabreezes kick in, possibly NE. 

Longer Term (Aug30) and beyond

Interesting set-up to end August with. Remnants of this weeks Tasman low look to reform on the other side of the North Island but at the stage the resultant low is just a bit too far south to be in the swell window,  although models do show it moving north, right to the edge of the swell window , so we’ll flag it and keep and eye on it. 

High pressure in the Tasman has a downstream blocking effect on a series of powerful approaching frontal progressions and lows in the Southern Ocean suggesting supressed swell activity from the S as we move into the firsy week of Spring. We’ll take another look at that Wed but for now we’ve got bigger fish to fry.