Sydney Hunter Illawarra Surf Forecast by Ben Matson (issued Mon Sep 30th)

Features of the Forecast (tl;dr)

• Low point Tuesday with a small mix of swells
• New S'ly swell for Wed but tricky winds
• Building S/SE swells Thurs/Fri with good AM winds
• Large kick in SE swell from very late Fri, peaking early Sat, with good winds
• Easing size Sat PM thru' Sun/Mon
• More S'ly swell mid-next week onwards

Recap

Onshore winds marred surface conditions on Saturday as SE swells eased from 3-4ft. The onshore flow abated slowly on Sunday to become variable by the afternoon - and was offshore all day south from Sydney - as stronger E/NE swells built from 3-4ft to 5-6ft+ by lunchtime. We’ve seen excellent conditions this morning with easing swells from 4-5ft to 3-4ft, with early offshore winds maintaining clean conditions across the majority of the coast ahead of a southerly change.

Maroubra looking mighty fine Sunday morning

This week (Oct 1 - 4)

We’ve got a dynamic outlook ahead, though the next few days look a little tricky for surf.

Today’s southerly change will clear to the north-east overnight, leaving us with a more settled atmosphere for Tuesday - still southerly, but with a weaker synoptic influence, meaning there’ll be a decent chance for early land breezes in the morning. Overall wind strength should remain light to moderate.

Surf size will be an average mix of short period S'ly swell trailing the front, and easing E/NE energy from today. Size should manage 2-3ft at most open beaches though I’m certainly not expecting anywhere near the quality we saw this morning.

Another front will push along Southern NSW overnight Tuesday, clipping most regions before dawn with moderate to fresh S/SE breezes, though this system will also clear off the coast during the day and allow lighter onshore winds to settle through the afternoon. 

The E/NE swell will be easing back more by this time (slow 1-2ft sets), but we’ll see a slightly stronger mix of S and SE swells from a couple of sources, all essentially related to the same progression of fronts in the Tasman Sea. Don’t expect much more than 2-3ft at south swell magnets though. 

This frontal passage over the coming days is interesting, because we’ll see a continuing influence from it all the way through into the weekend.

The initial front pushing through the region today will merge with a broad low pressure trough in the central Tasman Sea by tomorrow, which will then slowly evolve into a Tasman Low. It’ll take a few days to get there, and will receive the greatest encouragement from the Wed AM frontal passage, which will inject a surge of very cold air into the intensifying surface trough, accelerating its development into a significant mid-latitude system by Thursday. 

The upshot is that we’re due to receive a large SE groundswell event overnight Friday into Saturday (from the synoptic chart below), but prior to then, Southern NSW will be the beneficiary of gradually building S/SE swells as the Tasman Low slowly broadens the post-frontal S’ly airstream around its western flank, and steers it a little more counter-clockwise through the swell window. 

This is kinda similar to what we see with many trade swell events in SE Qld and Northern NSW - the easterly flow gradually broadens and gathers strength, which in turn generates a slow but steady increase in size across the region, instead of the immediacy of a rapid swell increase born by a rapidly developing though isolated low pressure system.

The main difference is that in our case, it’ll generate sideband energy from the S/SE for us, which will only favour south facing beaches for the most size. 

So, after a slow start on Thursday morning, we can expect wave heights to build from the S/SE all day, reaching 3ft by the afternoon then into the 4-5ft range through Friday ahead of some very large sets arriving towards the evening (but more likely pushing through overnight).

As for local winds, a weak right of high pressure should allow light/variable flow both morning, with afternoon sea breezes from the NE (a little stronger Friday than Thursday). As such, there’ll be options pretty much everywhere (though beaches not exposed to the south will be much smaller). 

I'll fine tune things on Wednesday.

This weekend (Oct 5 - 6)

Our weekend SE swell is expected to peak Saturday morning with sets somewhere in the 6ft range at most coasts (up to 8ft at reliable swell magnets and bombies), abating slowly into the afternoon. 

Local winds are expected to remain favourable as a weak front crosses the coast; direction should be NW but we may see it veer to the west at some point.

Easing surf on Sunday will abate from 4-5ft early to 3-4ft throughout the day. The models are showing a secondary intensification within the Tasman Low (just off the West Coast of NZ) on Friday that could create a renewal of energy for Sunday, but at this stage it looks like it’ll be aimed mainly towards the Far South Coast and Tasmania. 

Sunday’s winds look a little tricky with a local trough possibly swinging the breeze ot the south, but I’ll have more idea on that in the coming days. 

Next week (Oct 7 onwards)

Easing conditions are expected into the start of next week, ahead of a renewal of southerly swell across the region from mid-week onwards as another series of strong fronts push from the Southern Ocean into the Tasman Sea. 

More on this in Wednesday’s update.