Craig

Mid Coast Thursday, South Coast Friday and early next week

South Australian Forecast (issued Wednesday 4th June)

Best Days: Thursday on the Mid, Friday down South, Sunday morning for tiny sliders on the Mid and peaky waves down South, Monday and Tuesday down South

Recap

Conditions started a little mixed down South yesterday with a variable wind from the western quadrant, but an afternoon W/NW'ly cleaned up conditions nicely in protected locations. The Mid Coast started off glassy but deteriorated during the day with the onshore W/NW breeze.

Today the swell started small and clean again across both coasts but a strong increase in new W/SW groundswell has been seen on the Cape du Couedic wave buoy with a sharp J-curve visible.

This swell should fill in later this afternoon and pulse to an easy 2ft on the Mid Coast with Middleton pulsing to 3-4ft and 4-5ft at Waits although winds are expected to swing onshore.

This Thursday and Friday (Jun 5 - 6)

As touched on above, the late increase in W/SW groundswell due this afternoon is on track with Cape du Couedic rising rapidly in size along with a jump in peak period to just under 16 seconds (pictured right).

This swell should peak this evening with a drop in size due tomorrow with the direction swinging more SW. This will be a result of the mid-latitude low generating the swell intially moving through our western swell window before then tracking through our south-western swell window last night.

In saying this the Mid Coast should continue to see 2ft sets tomorrow morning with larger 3-4ft surf at Middleton and 4-5ft waves at Waits and Parsons.

Winds will be good across the Mid Coast tomorrow with a light offshore SE'ly while the South Coast may see a lingering S'ly. Weak SW sea breezes are due across both coasts at some stage so aim to surf through the morning for the best conditions.

The swell should continue to ease through Friday but winds will continue to be favourable with light local offshores due across both coasts ahead of a slightly stronger SW'ly into the afternoon.

This weekend onwards (Jun 7 onwards)

The start of the weekend isn't looking too flash as an onshore change moves through just before dawn Saturday bringing with it fresh S/SW tending S'ly winds.

A new long-range W/SW groundswell should fill in on Saturday though and the Mid may be worth a look late as winds tend S/SE and the odd 1.5ft set sneaks through.

Sunday is looking better as the long-range swell from west-southwest of WA continues to 1-1.5ft on the favourable parts of the tide on the Mid while the South Coast sees a new SW groundswell generated in the wake of Saturday's change. Middleton should offer sets in the 3ft range, while Waits should see bigger 4ft+ waves. Winds should be offshore from the E/SE across the Mid while the South Coast won't be too tidy with a morning E'ly (favouring protected locations).

Monday and Tuesday are looking much better down South with an easing swell and offshore N/NE winds during the morning on the former and all day fresh N/NE winds on the later.

Longer term there's nothing major on the cards until later Friday and more so the following weekend. A strengthening node of the Long Wave Trough is forecast to move in across WA mid next week and with this we should see some stronger and more familiar winter frontal activity.

A series of medium sized plus W/SW-SW groundswells on the cards from next weekend onwards but Check back here on Friday for confirmation of this.

Comments

cmrls23's picture
cmrls23's picture
cmrls23 commented Wednesday, 4 Jun 2014 at 10:54pm

Hi Craig,

when I'm looking at the cdc wave bouy, how long does that generally take to reach the mid coast? for the peak in the graph today at around 1pm, what time would you expect that to hit the mid?

cheers

Craig's picture
Craig's picture
Craig commented Thursday, 5 Jun 2014 at 10:31am

Great question cmrls23.

There's a couple of simple equations.

Get the average peak period which was around 15s and multiply by 2.81 and you'll get the speed of the swell in km/h.

So 15x2.81 = 42.15km/h

The distance from the buoy to the Mid Coast is about 180km so that's a travel time of just over 4 hours. If the period is higher it will travel quicker and if lower, slower.

cjt101's picture
cjt101's picture
cjt101 commented Thursday, 5 Jun 2014 at 8:01pm

Hi Craig
Thx for the forecaster notes, I've always struggled to understand the wave period, and how this data is read and interpreted. Can u give a real quick summary of how the wave period in seconds effects the swell hitting our coasts.
Thanks

Craig's picture
Craig's picture
Craig commented Friday, 6 Jun 2014 at 10:23am

It's really hard to sum it up in a few sentences as there's a lot to take in here, but I'll try my best. (Will put together an article when I get the time).

The swell period is the time between consecutive wave crests/troughs passing one particular point and is an indication of how strong the swell is.

Each storm creates winds across an area of ocean and this is called a fetch. Now the stronger the winds within the fetch as well as the bigger the fetch area and longevity of the fetch, the larger the swell will become and also the larger the swell period.

So large strong storms create large, long period swells and weaker, close-range systems like a short-lived cold front moving through will kick up a low period and weaker windswell.

The larger period swells are stronger because they store more energy below the ocean surface which was transferred from the strong winds over the ocean, and the larger the swell period, the deeper this energy goes into the water column (hundreds of metres below the sea surface).

As this energy deep within the water column starts to reach shallower water it has nowhere to go except to be compressed and start to rise in size (visible as an incoming set wave out to sea) before it all becomes too much and breaks on a reef or beach.

Because longer period swells have more energy below the surface, these waves will have a lot more power and push compared to a lower period swell which won't have anywhere near as much energy.

While long period swells have more energy and power, the interaction of the energy in the water column with the ocean floor (bathymetry) allows them to also refract and focus or be deflected away or into certain parts of the coast/reefs/beaches.

That's why long-period groundswell lines can swing into very protected spots (albeit without too much size), while low period windswells will march straight past and not spread in at all. It's because the longer-period swells can 'feel' the ocean floor and be steered in certain ways.

Any further questions, fire away!

sir ambrose beachfucker's picture
sir ambrose beachfucker's picture
sir ambrose bea... commented Friday, 6 Jun 2014 at 12:43pm

What is the biggest clean swell to ever be surfed on the mid coast
and proof it happened with a photo.

Craig's picture
Craig's picture
Craig commented Friday, 6 Jun 2014 at 12:57pm

There was a clean glassy swell last year that got to 5ft on the sets. Heard some breaks were closing out.
But here's some screen grabs of the South Port Cam showing how big it was on that 3-5ft day!
2nd September 2013:

I think this was from another day though...

www.swellnet.com/photos/swellnet-sessions/mid-coast-full-flight

Charlie Brown's picture
Charlie Brown's picture
Charlie Brown commented Sunday, 8 Jun 2014 at 9:58am

Triggs

Charlie Brown's picture
Charlie Brown's picture
Charlie Brown commented Sunday, 8 Jun 2014 at 9:58am