Analysis: Intrusion of the East Australian Current

Craig Brokensha
Swellnet Analysis

Over the last week or so, ocean temperatures have really heated up across the East Coast.

Most noticeably, the temperatures across Sydney and southern NSW have been about as warm as it gets, with inshore temperatures of 24 degrees. The MHL Sydney waverider buoy, positioned 10km off Long Reef, has been recording peak sea surface temperatures just over 25 degrees since last Friday.

The Mid North Coast has had some small scale upwelling which has suppressed temperatures, though they rebounded late last week and over the weekend while up off the North Coast and SE Qld, the Byron and Tweed Head buoys have registered temperatures of 27 degrees.

Around this time of year we usually see an increase in ocean temperatures across southern NSW from the East Australian Current (EAC). The EAC is a western boundary current - it forms the south-west border of the Pacific Ocean - that flows southward from the Coral Sea, down along the East Coast before usually splitting from the coast around Seal Rocks and heading eastward towards New Zealand, known as the Tasman Front.

Any remaining flow heading south of this is known as the EAC Extension and can reach as far south as Tasmania before meeting the Antarctic Circumpolar Current. The flow is strongest during the summer months and varies year on year regarding its intrusion south towards Tasmania.

Having a look at the current satellite imagery of the sea surface temperatures off the southern NSW coast above, you can clearly see the EAC pushing into Sydney and then further down, to a position south-east of Eden.

While it's normal for the EAC to travel this far south, what's not normal are the temperatures. 24-25 degree water is sitting very far south, and comparing this to the long-term climatic average, it's 3-4 degrees warmer than average.

While more pleasant for surfing, there are long term implications if the EAC regularly begins pushing this far south. For one, we'll see more tropical fish species setting up habitat further south, while for Tasmania, the incursion of sea urchins on the East Coast pose a real threat to the rocky reef systems and ecology.

Satellites are constantly measuring the sea surface temperatures from above, scattered throughout the world's oceans are small observational buoys called ARGO floats. These floats have been deployed by various international organisations and institutions with the data freely available for all to use.

The floats measure salinity and temperature throughout the ocean column while also being at the mercy of the world's currents, hence providing real-time feedback of the speed and direction of such currents.

You can view the location and history of the ARGO floats around the world here and luckily we've seen one such float travel southward with the East Australian Current the past few months.

Observations start through October when it was positioned well east of Byron Bay, meandering for the month before being swept south in the EAC from mid-November. Once travelling south it covered ground steadily and travelled the 350km from Seal Rocks to its current position east of Jervis Bay in 21 days. That's an average of 20cm/s or 700m/hr.

ARGO float 5905440 movement south from September 2019 through January 2020

It's still currently sitting east of Jervis Bay and we can examine the temperature profile through the water column. On the surface temperature have maxed at 25.536 degrees, while temperatures are still 20 degrees some 100m below the surface (the pressure in decibars is approximately equal to the depth in metres).

Moving back up the coast off northern NSW and it's worth considering the minimum ocean temperatures needed for cyclone formation, that being approximately 26.5 degrees. The current temperatures off Byron are easily within this threshold. However, what we also need is the mixed layer below the surface to contain these temperatures, otherwise the cyclone will quickly weaken once using the energy from the surface water.

Regarding the swell potential from this increase in water temperature over the coming months, it all depends on whether we get the right synoptic setup and instability aloft. We'll have to watch it closely and cross those fingers for a more classic autumn of surf compared to recent years.

Comments

thermalben's picture
thermalben's picture
thermalben commented Tuesday, 28 Jan 2020 at 3:04pm

Thankfully it's cooled to 26 degrees at the Tweed buoy. The SST trend over the weekend was a little ridiculous.

thermalben's picture
thermalben's picture
thermalben commented Tuesday, 28 Jan 2020 at 3:10pm

On the other hand, North Straddie just reached 28 degrees.

warddy's picture
warddy's picture
warddy commented Tuesday, 28 Jan 2020 at 3:47pm

I went for a Standup paddle in the Canals around Mermaid Waters today for a bit of cardio ..
Couldn’t believe how warm the river was and that’s after all the rain too ...
Been here over 30 years and never felt it like that...

stanfrance's picture
stanfrance's picture
stanfrance commented Tuesday, 28 Jan 2020 at 4:33pm

Tipping points Ben, what are the triggers for real change in global oceanic circulation patterns?

Stan France

the_b's picture
the_b's picture
the_b commented Tuesday, 28 Jan 2020 at 4:42pm

Check out the sst charts for late jan 2001. 26deg on the nthn beaches, stinking hot in boardies. 28deg on the coast around coffs

Craig's picture
Craig's picture
Craig commented Tuesday, 28 Jan 2020 at 4:46pm

The_b.. wow! Found it, incredible!

yocal's picture
yocal's picture
yocal commented Friday, 31 Jan 2020 at 9:38am

Wasn't the last IOD event in 2001? Or was it 2011?

If it was, maybe there's a link.

Go deeper Taylor, go deeper!

Craig's picture
Craig's picture
Craig commented Friday, 31 Jan 2020 at 9:50am

Can't see any link here..

Last strong event 2006 and before that 1997..

freeride76's picture
freeride76's picture
freeride76 commented Tuesday, 28 Jan 2020 at 4:53pm

Might be bath warm on the Byron buoy which is 6 nm E of the Ballina bar but inshore nor- easters are keeping it much cooler than that.
I’d say 21-22, which is nothing special.

Craig's picture
Craig's picture
Craig commented Tuesday, 28 Jan 2020 at 5:04pm

Yes you're right, but I tell you when I was up on the Goldy last week I wore a long arm vest as The Tweed was cooler and it was raining with a southerly wind. I've not been so hot in water like that. Would have to have been 26 degrees or so.

The warmth is just north of you..

lostdoggy's picture
lostdoggy's picture
lostdoggy commented Tuesday, 28 Jan 2020 at 5:13pm

I did the same.
Was cool and drizzly and I was up at cooly from ballina.
Put the vest on and had to get out of the water as I was sweating.

Craig's picture
Craig's picture
Craig commented Tuesday, 28 Jan 2020 at 5:17pm

Was crazy eh!

gingeryeti's picture
gingeryeti's picture
gingeryeti commented Tuesday, 28 Jan 2020 at 4:56pm

Was cool and green on sunshine coast on Saturday. I normally run about 110 kilos but I think I shrunk in the cold water.

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming commented Tuesday, 28 Jan 2020 at 5:02pm

Vicco water now feels nice and warm and starting to get a fish species pop up we don't always see, Blue fin tuna, Yellow tail king fish etc

mvfitzy's picture
mvfitzy's picture
mvfitzy commented Tuesday, 4 Feb 2020 at 11:55am

We've been getting SBT and Kingies in Western Vicco for many years, along with a random mahi mahi mixed in the schools too.

Fitzy

freeride76's picture
freeride76's picture
freeride76 commented Tuesday, 28 Jan 2020 at 6:29pm

just went for a fish then.water cool-ish and still full of cornflake weed.

20 knots of nor-easter and 2ft of gurgle.

no fish.

it's not unusual for a 26 degree surge from the EAC, in fact that first surge of cobalt blue warm water usually comes in December.

whats interesting now is how the interplay between the EAC and upwelling tendencies play out.

doesn't look to be any breakdown of the northerly pattern and a return to Tradewinds into the first week of Feb.

Oink's picture
Oink's picture
Oink commented Tuesday, 28 Jan 2020 at 6:32pm

Does water temp increase blueys?

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming commented Wednesday, 29 Jan 2020 at 8:03am

I believe they are found in quite a big temp range and in Victoria mostly caught out deep off Portland, but there has been a few showing up and getting caught between Phillip Island and Cape Shank, maybe it's more to do with warmer water bringing in schools of bait fish or something?

No sure

Craig's picture
Craig's picture
Craig commented Wednesday, 29 Jan 2020 at 8:06am

No, but seeing as the warm water has come from the Coral Sea there is more chance for blue bottles to be present. They haven't been bad this year in Sydney and we here at Swellnet think that's because there hasn't been any sustained trade-flow blowing then in from the Coral Sea. Just local north-east winds that don't extend far into the Tasman/Coral Seas.

Halfscousehalfcockneyfullaussie's picture
Halfscousehalfcockneyfullaussie's picture
Halfscousehalfc... commented Tuesday, 28 Jan 2020 at 7:31pm

So what was the outcome in autumn in 2001? I remember the snow season was shit and that big clean July swell. Too many beers since then. Ha

freeride76's picture
freeride76's picture
freeride76 commented Tuesday, 28 Jan 2020 at 8:07pm

TC Sose Apri 2001, one of the biggest, cleanest swells ever.

Halfscousehalfcockneyfullaussie's picture
Halfscousehalfcockneyfullaussie's picture
Halfscousehalfc... commented Tuesday, 28 Jan 2020 at 8:26pm

We can only dream I guess

r-clay's picture
r-clay's picture
r-clay commented Wednesday, 29 Jan 2020 at 7:14am

I recorded 29 deg water off moreton a few weeks ago, the sharks have been going mental on the sunny coast too.

mac396's picture
mac396's picture
mac396 commented Wednesday, 29 Jan 2020 at 7:47am

There has been a big clockwise eddy down here off SE Tasmania dragging cold water up from down south. Our water is currently much colder than recent years down here ....

thermalben's picture
thermalben's picture
thermalben commented Wednesday, 29 Jan 2020 at 9:11am

Which part of SE Tas? Storm Bay, Bruny Island, Eaglehawk Neck? Just curious to see the associated SST charts.

Fatnuts's picture
Fatnuts's picture
Fatnuts commented Wednesday, 29 Jan 2020 at 1:21pm

Tassie's East coast has been considerably colder than usual as has the south- A bit warmer right up in Frederick Henry bay shallows as expected but cool compared to the norm.The warm water is out off the coast but inshore more like middle of spring. Last year I got away with wearing a springy from Nov to April but so far this year its been fecking cold

mac396's picture
mac396's picture
mac396 commented Wednesday, 29 Jan 2020 at 9:37pm

The eddy seems to have subsided a bit now but a weaker version can still be seen on the SST images.
I work for CSIRO Marine Research here in Hobart and we deployed a Slocum underwater glider from Maria Isaland a couple of weeks ago to zig zag south across the EAC and then up into Storm Bay.
On Sunday the southern current close to the coast was running at around 3/4 knot northward and our glider was going backwards as our max velocity is approx 1/2 knot.
We have since progressed south ok since Monday.
We are only measuring around 16.5 degree water on the surface just now which also shows on the SST images http://oceancurrent.imos.org.au/sst.php
The water is cold right down our East Coast and the Storm Bay beaches so far this year, the coldest for many years at this time of year, lots of complaining.
It is probably mainly due to the constant westerley wind patterns we have been getting causing upwelling.

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno commented Wednesday, 29 Jan 2020 at 9:19am

EAC Dude! Wonder how Crush the turtle is going... will have to read this more seriously a bit later :)

stunet's picture
stunet's picture
stunet commented Wednesday, 29 Jan 2020 at 9:21am

Hey VJ,

OT, but have you seen Inq - Crikey's investigative arm - are doing a series on Australia's eroding coast? Little lean on the details so far but they singled out a few places in West Oz - Two Rocks etc.

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno commented Wednesday, 29 Jan 2020 at 9:32am

Hi Stu, sorry no, been superbusy so not much time for lurking Swellnet or surfing for that matter - a couple of good sessions in this last swell when I had down time though. Will have a look.

Two rocks/Yanchep was one of the first "missions" I ever did to find waves, back when Burns beach was actually a separate little township - will have a look this arvo/tonight.

MidWestMonger's picture
MidWestMonger's picture
MidWestMonger commented Saturday, 1 Feb 2020 at 6:39am

West Australian subscriber and zero percent stakeholder in east coast water temps but your telling me:
A 'warm water tongue' has gone down on the NSW south coast.
Once tasting the sweetness of victorian waters has turned and formed a phallis out to sea.
And no comment or call for comment from Gary G. (the one person who can explain all of this)
Do we have to wait for Mallacoota to King Island to be teabagged?

freeride76's picture
freeride76's picture
freeride76 commented Saturday, 1 Feb 2020 at 7:04am

27.5 on the Byron Buoy yesterday.

simba's picture
simba's picture
simba commented Saturday, 1 Feb 2020 at 10:04am

surprised that with sea temps that hot that we arn't getting more rain.

simba

freeride76's picture
freeride76's picture
freeride76 commented Saturday, 1 Feb 2020 at 10:21am

I think a wet signal is looming Simba, when this next high sets up a deep, mean easterly flow.
lots of moisture inbound.

Distracted's picture
Distracted's picture
Distracted commented Saturday, 1 Feb 2020 at 1:34pm

Mac365, do the westerly winds cause an Ekman Transport Effect off Tasmania for the upwelling as does the nor easter off the East Coast? The geometry appear different ?

Craig's picture
Craig's picture
Craig commented Saturday, 1 Feb 2020 at 3:24pm

East Coast Tassie, north to north-easters provide upwelling, and for the southern coast, it'd be east to south-easters.

tango's picture
tango's picture
tango commented Saturday, 1 Feb 2020 at 4:25pm

Great article, Craig and good to see.

One thing, though - my understanding is that fish don't generally "set up habitat" or even influence it unless they have a long-standing or intense impact on their environment. Their range/distribution might change in response to factors such as temperature, as in this case with warm water moving south and the fish in that temp range move with it, and then potentially utilise or impact the habitat of other species. Or if they're pelagics, their own habitat (eg the upper water column) might move as temperatures/DO levels/food sources move. Pedantry, perhaps.

1973bro's picture
1973bro's picture
1973bro commented Saturday, 8 Feb 2020 at 8:20am

Wonder how long before the dreaded Box Jellyfish is drawn further down the coast in these currents?