Sydney, Hunter and Illawarra Surf Forecast (issued Wednesday 19th March)

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thermalben started the topic in Wednesday, 19 Mar 2014 at 3:53pm

Sydney, Hunter and Illawarra Surf Forecast by Ben Matson (issued Wednesday 19th March)

Best Days: Sun/Mon/Tues: very, very inconsistent E/NE groundswell with variable conditions.

Recap:  Easing E/NE groundswell all day Tuesday (with generally good conditions), reaching a low point today with very little swell left across the coast and freshening southerly winds.

This week (Mar 20-21)

Not much happening for the rest of the week. We’ll see a small, slow increase in swell from the E/NE from two somewhat related sources - some minor sideband energy from a restrengthening of the trades south of New Caledonia, and some short range energy from an E’ly fetch developing off the top of a small high currently pushing into the southern Tasman Sea. 

Wind speeds aren’t expected to be very strong so the resulting surf won’t be very big nor very powerful but we should see a couple of feet of peaky waves across the open beaches by Friday. However, freshening north-easterly winds will keep conditions below average (look for light variable winds Thursday morning tending onshore in the a'noon). Overall, keep your expectations low.

This weekend (Mar 22-23)

Saturday looks a little average at this stage, but there’ll be waves. We should be close to the top of the swell cycle for the aforementioned E/NE sources plus some local NE windswell thanks to Friday's winds - but that’s only likely to contribute maybe 2ft+ at exposed NE facing beaches if we’re lucky. It'll be smaller at south facing beaches. 

A small low pressure system is expected to develop east of Bass Strait overnight Friday, and this will drive a weak southerly change along the coast - reaching the South Coast on Saturday morning and Sydney sometime early evening. Depending on the timing of this change - if and when it arrives - we could see a few options open up across the region for the afternoon. 

On Sunday, we’re going to eventually see the arrival of some long period E’ly groundswell, currently being generated right now by a deep monsoon trough near the Cook Islands in the South Pacific. 

In fact, embedded within the northern periphery of the trough is recently-formed TC Mike, which is expected to intensify and track south into the belly of the system, giving it a turbo-charge. This greater synoptic feature is itself expected to move only slowly southwards, and with wind speeds likely to top 50-60kts at its core, it’ll generate a large long period swell for the South Pacific.

As was discussed on Wednesday, this looks to be an eerily similar synoptic setup to TC Lusi, which generated the Sunday/Monday swell we’re all still frothing on.

But. BUT! This system is almost twice the distance from the mainland as what TC Lusi was (around 4,800km - see chart below), and the ramifications of this will be considerable at the Australian coast.

Firstly, despite TC Mike moving more favourably slower than TC Lusi, and displaying a more robust fetch, the swell decay over such an enormous distance means that we’re looking at much smaller waves heights in New South Wales.

An even more important factor is the swell consistency. Swells that travel such vast distances often display breaks between sets of fifteen or twenty minutes at a time, so expect a lot of waiting around for the bigger waves. 

As for size - first up, we’re looking at a peak on Monday. Sunday will begin with residual energy from Saturday, but the new E/NE swell should build throughout the day - however we probably won’t see the biggest waves from this source until Monday morning. So aim for a very late surf on Sunday if you’re looking to maximise the size potential from this swell (somewhere between 3ft and maybe 5ft by dusk). 

And winds? Overall we should be OK. The small low expected to form east of Bass Strait early Saturday is modelled to slip to the south-east, leaving us in a trough pattern across much of southern NSW on Sunday. Which probably means variable winds and sea breezes. 

It’s also worth mentioning that the small low developing east of Bass Strait has split the model guidance right now, and although it probably won’t generate much, if any swell for us - it may kick up a small south swell into Sunday (2-3ft for exposed south facing beaches). I’d rate this a low to moderate chance right now though. 

Next week (Mar 24 onwards)

Righto. So how big is this E/NE groundswell likely to be? 

I think we’re looking at most locations pulling in extremely inconsistent set waves between 3ft and maybe 5ft by lunchtime Monday. If you’ve got a particularly reliable swell magnet or bombie that accentuates long period easterly swells particularly well, then rogue 6ft+ sets are certainly possible. But overall, most of your surfing will be done at the lower end of these size estimates. 

Local conditions also look like they may be rather mixed, as another southerly change is expected to move along the coast on Monday morning. While southern corners will remain clean, exposed beaches will become bumpy. There’s a reasonable chance that the early morning will offer a period of SW winds but we are certainly at risk (at this stage) of a fresh southerly ruining many locations at the height of this swell event. The southerly may also contribute a low quality windswell to the mix (which won’t be very welcome anywhere). 

A slow easing trend of this E/NE groundswell is then expected through Tuesday, and due to the forecast position of the Long Wave Trough at this point, persistent S’ly through SE winds are certainly quite possible. 

Looking beyond Tuesday and there are no major swell events lining up on the cards at this point in time. In fact it appears that we may have exhausted our supply of tropical swell sources for the next few weeks, which suggests new activity through the first half of April will originate from either the Southern Ocean (i.e. S’ly swells) or the Tasman Sea (S/SE thru E/SE). So if an E/NE swell direction plays a strong influence in the quality of the surf at your local I’d highly recommend making the most of this Sun/Mon/Tues event.

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lolo commented Wednesday, 19 Mar 2014 at 4:30pm

Hmm,

Leaving for a romantic week away with the missus to Lord Howe Island on Saturday.

Looks like I might have to sneak a board in somehow by the look of those WAMS....

thermalben's picture
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thermalben commented Wednesday, 19 Mar 2014 at 4:38pm

Will be interested to see how you get on! There's not many spots on the east coast - just a few reefs (not sure how they handle size) and then Blinky Beach (which probably won't handle it at all). Winds should be good though. Take some photos!

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Ralph commented Wednesday, 19 Mar 2014 at 4:55pm

given the long distance of the swell source do you reckon there will be much deterioration in swell energy as you move down the coast from Sydney?

thermalben's picture
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thermalben commented Wednesday, 19 Mar 2014 at 5:13pm

No real reason for any major size loss on the South Coast although this system will slip into the swell shadow of New Zealand over the coming days so smaller waves are possible at a point 'south of Sydney', especially in the Far South of the state.

But at what location on the coast would we see size start to taper off - where is this theoretical point 'south of Sydney'? That's one of the more difficult questions for a swell event like this. Personally, I reckon you'd be reasonably safe down to about Jervis Bay or Ulladulla.

But in order to maximise your chances of quality waves from this event I'd recommend a trip north of Sydney instead. Heading south will certainly be riskier.

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Joeseph commented Wednesday, 19 Mar 2014 at 6:56pm

Hey Ben, really appreciate these notes they give so much more info than forecast graphs.

I've studied a little meteorology and I'm curious to too know what role (if any) the local topography plays on winds. Generally I surf between ulladulla and moruya and in the last two weeks there have been two occasions where the winds either side of batemans bay have been blowing at opposite direction. The first occasion I dismissed it as localised wind (no dominating systems were around) creating onshore winds to the south and offshore winds to the north of BB. But the second occasion was last Sunday, when the strong westerlies dominated the east coast south of BB winds were ese all day... Is this transition zone of wind direction coincidental or perhaps related to the topography of the area?

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rusty-moran commented Wednesday, 19 Mar 2014 at 8:07pm

Joseph, I can imagine you are feeling the frustration of checking onshore waves all day then seeing the photos of crisp offshore waves everywhere else.

However those winds (westerly winds just to the north of Ulla, but ese winds to the south of Ulla) were precisely predicted by the bom model a few days ahead of Sunday. Although not a hind cast, here is the model link http://www.bom.gov.au/marine/wind.shtml?location=nsw&tz=AEDT

Ben might be able to explain why such a small high pressure ridge only formed around Eden and didn't upset the westerly flow just north at Ulla Dulla.

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mcbain commented Wednesday, 19 Mar 2014 at 8:31pm

Speaking to local sailors - they often confirm distinct wind changes at around Durras Mountain, which is pretty much where the line was on sunday.
Topography would be my guess too. North of Durras, pretty much at Ulladulla - the Sydney sandstone lansdcape begins, and the Buddawang escarpment gets quite close to the coast. I wonder if this relatively sharp change in elevation close to the coast, compared with more undulating landscape and escarpment further west south of Ulladulla (Moruya and onwards) has anything to do with it.

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Craig commented Wednesday, 19 Mar 2014 at 9:00pm

I'd say the difference in winds on Sunday would of been due to the presence of a trough line, but would need to check the charts in more detail to confirm.

Have also heard that the winds around Mt Durras have a mind of their own, but whenever I've gone to surf either south or north of there, winds have been as expected.

Not related to wind, but you bring up a great point mcbain re the change in geology south of say Batemans Bay/Durras.

The volcanic black rock found around Bawley and surrounds which creates some of the best setups across the coast disappears to the south, and as a result there aren't anywhere near as many setups compared to the area north of Batemans.

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thermalben commented Thursday, 20 Mar 2014 at 7:49am

Thanks for the nice words Joseph. As Mcbain and Craig have said above, local topography probably played an influence. Although a front pushed through southern NSW on Saturday morning, the pressure gradient wasn't overly tight (see chart below) and winds behind the change weren't especially strong.

One factor that supports the theory of local topography influencing the winds around Batemans is that Green Cape was mainly W/SW on Sunday (veering S/SW for a period in the a'noon).

However, Montague Island was S/SW early, before swinging S'ly then E/SE throughout the day. Typically, Montague Island is a good indicator for the broad synoptic flow (which should have been W/SW), of which wind strengths are often 15-20% higher here due to its offshore location and slightly elevated position (52m AMSL). Winds were by comparison quite light on Sunday (15kts, gusting 20kt, easing in the a'noon). Merimbula also veered E/SE in the afternoon. 

I would have thought that any topographical influence from Mt Durras wouldn't have penetrated quite as far south as these locations. Therefore, under the lighter pressure gradient in the wake of the front, perhaps this was more of a sea breeze effect? The timing and anti-clockwise rotation of the winds would support this theory.

In actual fact, perhaps it was a combination of both - the local influences counteracting the synoptic flow, therefore allowing a sea breeze to develop. This is also supported by general sea breeze theory, which is (to be brief): synoptic NW winds above a certain strength threshold in southern NSW will often prevent a sea breeze from developing at the coast. And check the observations from Ulladulla - NW thru' W/NW all day Sunday. Hence why we didn't see a sea breeze here at all.

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Joeseph commented Friday, 21 Mar 2014 at 9:09am

Cheers for all the info, plenty of things to mull over. Luckily I spent most of the day in offshore conditions and only spent an hour so in the car questioning whether I should get the motto 'Never drive away from good waves' tattooed on the back of my hand. Rusty, I did notice the earlier forecast of onshore conditions on the southern tip on NSW, but the BoM model on Saturday afternoon changed to offshore all day. I think as Ben says, it was a combination of both as I was told the winds at Moruya started NE and swung around to the E then ESE, meaning interrupted synoptic flow and a sea breeze early before the ESE change.

As for the geology, the basalt intrusion at Bawley is quite special, such a good gradient for creating waves. There is another similar intrusion between Batemens Bay and Moruya that forms one of the better (and only reef breaks) in that area. The Sydney Sandstone Basin actually starts just south of South Durras and north of North Head, you can actually walk in and see it change (but there definitely aren't any reef setups south of Bawley;). Interestingly, the formation of the coastline and escarpment south from BB is yet to be explained by any concrete theory.

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Craig commented Friday, 21 Mar 2014 at 9:12am

Yep, know the coast well, that one spot you speak of I've yet to seen properly fire but hear it's amazing..