East Australian Current Brings the Christmas Warmth

Craig Brokensha picture
Craig Brokensha (Craig)
Swellnet Analysis

November 2021 was one for the record books.

Across Australia it was the wettest November on record, and it was also the coolest November in 21 years.

To find out why we have to look inland, as it's there - in Australia's interior - where our warmth originates. This year, however, the inland failed to heat up through spring owing to the constant in-feed of moisture and cloud from the north-west of the country (thanks to the negative Indian Ocean Dipole). We also saw similar instability and moisture feeding in from the Pacific Ocean to the north-east thanks to the developing La Niña.

The formation of coastal lows and troughs blanketed the coast in cloud while ocean temperatures remained stubbornly cool.

Switch to the start of December, and while the cloudy, cooler weather and intermittent rain storms are persisting thanks to La Niña, we've seen the water temperature rocket upwards in NSW - at least as far south as Wollongong.

Where has this warm water come from and is it normal?

Under a La Niña setup (with tropical winds blowing towards the west) we get warm water piling up across the western Pacific Ocean and this then starts flowing north and south away from the equator, under the influence of the Coriolis Force due to the Earth's rotation. These currents flowing on the western side of ocean basins are known as Western Boundary Currents and transport warmer tropical waters towards the poles. A return flow along the eastern sides brings cooler water towards the tropics, with the complete circulation known as an ocean gyre.

For the Northern Hemisphere we have the Kuroshio Current and Gulf Stream flowing on the western side of the north Pacific Ocean and north Atlantic Oceans respectively, providing warm water to Japan and north-east America.

For the south Pacific Ocean we have the East Australian Current (EAC) and the Agulhas Current for the Indian Ocean.

The EAC originates in the Coral Sea where sea surface temperatures are currently warmer than normal (1.5-2.5°) thanks to the current La Niña setup. It flows southwards down the Qld and NSW coasts, sometimes reaching as far as Tasmania. 

The EAC flows all year but is strongest during summer and usually separates around Seal Rocks, travelling east towards New Zealand. This is known as the Tasman Front.

The East Australian Current flowing south down the East Coast from the Coral Sea

The remaining current pushes south in fits and bursts, spawning off tongues and eddies which, while inducing coastal upwelling, also provide warmer water to the southern NSW region. 

One such intrusion has recently made its way south over the past two weeks and has brought bath-like water to the Hunter, Sydney, and Illawarra regions. From my personal observations, it feels like it's sitting at 21-22° while the MHL wave buoy positioned 10km off Long Reef in Sydney is currently recording temperatures of 23°. Further up the coast temperatures are 25° off Coffs Harbour and 26° off Byron Bay.

What's helped bring this water in so early is the lack of north-east winds that usually plague the coast in summer. These persistent north-east winds promote upwelling of cooler water, but with back to back lows and troughs forming off the coast, bringing southerly winds, the EAC has been allowed to fill in the near-shore zone. The opposite occurs in El Niño events with strong episodes of north-east winds and frigidly cold water upwelled along the East Coast (think of those Mid North Coast Christmas surfs in winter wetsuits).

Sea Surface Temperature observations from the 13th of December. The warm water intrusion into the Sydney region can be clearly seen.

The southwards intrusion is shown clearly in the above image, but you can also see that the EAC hasn't quite reached the Shoalhaven region or south of Jervis Bay yet, with it sitting further offshore, while off the far South Coast the water is still quite cool and below average.

Now that the warm is in, it should be here to stay during summer, with more warm water poised to flow down from the north. This takes into account the current La Niña setup which is less conducive for strong north-east wind events to develop owing to the sub-tropical high sitting further south. The South Coast should start to see the warmer water filling in over the coming weeks as the tongue extends gradually further south.

Comments

john.callahan's picture
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john.callahan Tuesday, 14 Dec 2021 at 2:07pm

Nice feature, Craig - all that extra La Niña induced warm water near the equator has to go somewhere, pushed south along the East Coast by the Coriolis effect.

The lack of NE winds to induce upwelling of cooler waters keeps the warmth intact.

science's picture
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science Tuesday, 14 Dec 2021 at 3:15pm

Picked the wrong 2 weeks to go hiking in November - rained every day bar one which was still overcast. The sun came out for an hour on day 10 and the mood lift was very apparent. Otherwise no sun or stars basically the entire time, an interesting psychological experiment.

Anyway warmer water can increase the intensity of cyclones can't it?

Craig's picture
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Craig Wednesday, 15 Dec 2021 at 7:23am

Agh bummer! What state?

And yep, tropical cyclones need sea surface temperatures of 26.5° or higher to maintain their strength and intensity. So warmer water and a deeper mixed layer will see cyclones become stronger and longer lasting.

There are other factors as well such us upper wind shear (read upper winds) which when strong will rip the structure of the cyclone apart, causing it to break down. If light the cyclone can continue on as is.

science's picture
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science Thursday, 16 Dec 2021 at 8:18am

NSW, Hunter/Yengo area.

Thanks for the info, especially upper wind sheer I hadn't considered that. Can't imagine waters being consistently above 26.5°, I know that's normal in the tropics but being coastie/newy my whole life I probably haven't felt much over 23°. Moving to Melb next year for study I dread whatever ridiculous temp that will be - (un)fortunately I won't have the time or transport to find waves.

Craig's picture
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Craig Thursday, 16 Dec 2021 at 8:25am

Yeah tropical lows/cyclones are fascinating. Once up and running they are steered by the upper level winds, hence once moving south/north from tropical regions they get swept away by the westerly jet stream.

This is shown clearly here in this image of cyclone tracks/intensities.

science's picture
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science Thursday, 16 Dec 2021 at 1:16pm

Cheers for the info and image. I see (super) Typhoon Rai is currently feeding off 29c water and about to make landfall. Hopefully that jet stream kicks in but it's not modelled to drift north until it reaches Cambodia.

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science Thursday, 16 Dec 2021 at 2:13pm

Vietnam*

Spuddups's picture
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Spuddups Thursday, 16 Dec 2021 at 3:46pm

That's a cool chart. Fark Japan gets hit by a lot of Typhoons. I think I read somewhere that the average is around twenty per year in the vicinity of Japan. Also it's surprising how far north hurricanes track in the Atlantic, towards Great Britain. I guess it's something to do with the Gulf Stream?

Craig's picture
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Craig Thursday, 16 Dec 2021 at 4:15pm

Yep, the Gulf Stream transports warm water far north

That transition from yellow to green is at 25°..

Spuddups's picture
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Spuddups Tuesday, 14 Dec 2021 at 4:52pm

Hey Craig, another good article, thanks. You mentioned that the East Australian Current heads off towards NZ. I've heard it said that it clips the SW corner of the South Island around Fiordland. I've done a bit of surfing down there. One time around Christmas the water was around 20', which would surprise a lot of people considering how far south it is. At that time of year it's generally around five degrees cooler in Dunedin, which is at a similar latitude, but is on the SE coast. Anyway, do you reckon this sort of thing could have anything to do with the East Australian Current?

Craig's picture
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Craig Wednesday, 15 Dec 2021 at 7:10am

Thanks Spuddups. It actually travels straight across towards the North Island and doesn't meander much below this. It then flows on as the East Auckland Current.

The Tasman Sea as a whole is warming faster than other regions and I'd say there'd be warmer water flowing in across the south from the west (though not the EAC proper).

There's some great info here about the currents around New Zealand, which there are many!

https://teara.govt.nz/en/ocean-currents-and-tides/page-1

Spuddups's picture
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Spuddups Thursday, 16 Dec 2021 at 8:19am

Cheers Craig. I never realised it was such a complicated system.

Craig's picture
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Craig Thursday, 16 Dec 2021 at 8:28am

Yeah there's a bit going on around New Zealand eh!

Distracted's picture
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Distracted Thursday, 16 Dec 2021 at 4:09pm

Also shows why the fishing is so good around NZ, highly variable bathymetry and currents coming from various depths and origins.

spinafex's picture
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spinafex Friday, 17 Dec 2021 at 11:24am

They were wearing boards in the north west of the South Island in November this year

stunet's picture
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stunet Tuesday, 14 Dec 2021 at 6:02pm

Just had a session skinning it, boardies, no vest.

Three days ago there were crew in full steamers and hoods.

memlasurf's picture
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memlasurf Tuesday, 14 Dec 2021 at 11:12pm

Craig when will it hit Victoria? I know some years it gets really warm.

Craig's picture
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Craig Wednesday, 15 Dec 2021 at 7:18am

The cooler temperatures in Bass Strait are more linked to the solar inputs (or lack of during the spring due to the cloud and rain) and tidal mixing in from South Australia on the western side and East Australian Current when it does reach Tasmanian latitudes on the eastern side.

So there's a lag at the moment and temperatures likely won't reach as high as normally seen through this summer. It'll be interesting to see how the EAC flows down into autumn.

carpetman's picture
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carpetman Wednesday, 15 Dec 2021 at 4:12pm

We get cool nearshore upwelling in eastern vic from extended periods of easterly winds. Can see it on the first figure.

Similar thing happened last summer. Most people in the water were wearing hoodies. 30C out. sub 14C in.

memlasurf's picture
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memlasurf Wednesday, 15 Dec 2021 at 4:26pm

Yeah doesn't seem to effect the MP as much although I have noticed it at Phillip Island if the easterly's have been around as you say, beautiful day and general water temp around 19-20º then drops to 15º. Also down the other side of Cape Otway, geez does that ever warm up that is freezing all year round almost gives Santa Cruz a run for its money. Reading how cold it is year round in the water I am surprised it is so busy with surfers (like 10-11º in winter and maybe a bit over 14º in summer which is much colder than here).

Spuddups's picture
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Spuddups Thursday, 16 Dec 2021 at 8:21am

Possibly the worst type of cold water; when it's a stinking hot summer's day and the water is freezing.

Craig's picture
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Craig Thursday, 16 Dec 2021 at 8:29am

I've got fond memories of surfing Port Mac (SA) with 40°+ offshore winds and being in a 4/3. The water gets colder than winter due to the strong upwelling in that region during summer.

Blowin's picture
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Blowin Thursday, 16 Dec 2021 at 11:29am

When the air is stinking fuvking hot, the water freezing fucking cold and there’s March flies landing on you as you sit out the back between sets you know it’s time to get to another state ASAP.

gheeto's picture
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gheeto Thursday, 16 Dec 2021 at 1:07pm

That sucks for fishing in Tas!

gheeto's picture
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gheeto Thursday, 16 Dec 2021 at 1:09pm

Sorry, first time commenting in here. I was referring to the warm water usually seen down in these lats this time of year

Craig's picture
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Craig Thursday, 16 Dec 2021 at 1:10pm

No reason to apologise. I understood and welcome.

Halfscousehalfcockneyfullaussie's picture
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Halfscousehalfc... Sunday, 19 Dec 2021 at 9:25pm

Now Craig, with all this warm water likely to pulse into autumn if we get a significant cold pool of air in April/may/June this is perfect ingredients for east coast lows…… so do the records align that after a La Niña there are significant ecl’s in the following winter?

Craig's picture
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Craig Monday, 20 Dec 2021 at 10:24am

Yep, exactly!

It's usually in the lead up year as we've seen the past two, but the ingredients are there into this coming autumn for decent swell producers.

memlasurf's picture
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memlasurf Monday, 20 Dec 2021 at 10:30am

OK enough about the east coast what ingredients to the southern facing coasts need? Something halfway between el nino and la nina we seem to be missing out a bit on ingredients in the past few years.

Craig's picture
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Craig Monday, 20 Dec 2021 at 10:38am

Yeah more towards El Niño, bring that storm track up closer to Aus and away from the pole eh.

dr-surf's picture
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dr-surf Wednesday, 15 Dec 2021 at 5:38pm

The Portland’s Boy’s know all about Cold Water. Surfing Bells is Noosa to them.

Spuddups's picture
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Spuddups Thursday, 16 Dec 2021 at 3:50pm

You mean Portland Oregon? Yeah, I know a guy who lived in that part of the world for the best part of a decade. Reckons it's generally around 8-9' year round. Hooded 5/4 wetsuits, gloves and booties. The air temp gets pretty hot in Summer as well.

thermalben's picture
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thermalben Thursday, 16 Dec 2021 at 9:51am

Tweed buoy showing 25 degrees right now, can't be far off in the surf too. Sublime.

Jono's picture
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Jono Thursday, 16 Dec 2021 at 11:02am

And this morning I saw two lads in steamers.

Craig's picture
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Craig Thursday, 16 Dec 2021 at 11:03am

And with no wind or cloud! Crazy, makes me hot thinking about it and not in a good way.

Craig's picture
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Craig Thursday, 16 Dec 2021 at 2:09pm

Down with the warm currents. Poor thing..

Craig's picture
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Craig Friday, 17 Dec 2021 at 6:47am

Incredible!

velocityjohnno's picture
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velocityjohnno Saturday, 18 Dec 2021 at 11:28am

High temps for Pilbara might take out records:

https://www.willyweather.com.au/news/40610/pilbara+could+set+new+austral...

Anyone who has worked there knows it can get fcknin hot, but over 49 must be another level

millsy351's picture
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millsy351 Saturday, 18 Dec 2021 at 1:27pm

And humming down the E seaboard....

Craig's picture
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Craig Saturday, 18 Dec 2021 at 2:40pm

How's the speed of the EAC at the moment.

2-2.5kt..

Spuddups's picture
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Spuddups Saturday, 18 Dec 2021 at 3:52pm

I don't know about you guys but I find this sort of thing fascinating.

Craig's picture
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Craig Saturday, 18 Dec 2021 at 4:31pm

Totally! The weather/ocean/atmosphere is never boring and always interesting. Constantly in flux as it tries to reach a never achievable equilibrium.

tango's picture
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tango Sunday, 19 Dec 2021 at 10:47pm

I'd be quite OK with an equilibrium of 4-6ft @ 16s, offshore and 22 degree water.

Craig's picture
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Craig Monday, 20 Dec 2021 at 10:23am

Ha!

steveb's picture
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steveb Tuesday, 21 Dec 2021 at 6:43am

Hi Craig, in the mid 70s I worked for CSIRO Fisheries and Oceanography Cronulla - they plotted the EAC using satellite-tracked solar powered free floating buoys, high tech then but probably redundant now. At the time they concluded the southward flow of the EAC was actually the eastern edge of a series of clockwise moving eddies, with northerly currents hugging the coast and southerly currents, the EAC, way offshore. Is that still the case some of the time or has that thinking been superceded?

Craig's picture
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Craig Tuesday, 21 Dec 2021 at 12:27pm

Hi Steve. When the EAC is further offshore (away) from the coast you can get small northward flowing currents and small eddies spinning clockwise, but eddies shedding off the EAC proper (containing warm water) spin anti-clockwise.

You can see the general flow (black lines) and eddies here..

freeride76's picture
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freeride76 Tuesday, 21 Dec 2021 at 8:36am

24 on the Byron Buoy but the last few days of N'lies have dropped the inshore temps significantly.

What's it like on the MNC?

Blowin's picture
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Blowin Tuesday, 21 Dec 2021 at 12:22pm

Definitely dropped. It’s not too bad though. 22ish in the surf I’d guess. I’d wager it’s much warmer not far out at all.

Crew in boardies but I’m in a springsuit.

Craig's picture
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Craig Wednesday, 22 Dec 2021 at 6:46am

The water went up another notch in-shore at Manly yesterday. Had to be 23° and with a few sea lice about. Incredible!

Craig's picture
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Craig Wednesday, 22 Dec 2021 at 6:48am

Latest update confirms this..

Looks like it's feeding further south now as well.

Sheep go to heaven's picture
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Sheep go to heaven Wednesday, 22 Dec 2021 at 7:10am

Push that sucker south and round the corner into Vic . We are still in full steamers here :( . looked like it was beginning to warm up a few weeks ago but a few strong southerlies put us right back to early spring temps . I don't think we've had warm summer water for maybe 3 years now ?

Craig's picture
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Craig Monday, 27 Dec 2021 at 5:06pm

The anomalies off the southern NSW region are 3-4° above average..

batfink's picture
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batfink Monday, 27 Dec 2021 at 5:43pm

Wow. Sea lice hey Craig. Went for a dip and later a surf yesterday. Have what I thought was a mozzie bite on my calf yesterday arvo, but it’s still there and hard and round. Sea lice might explain that. Annoying buggers. Up central coast atm. Water in Sydney and CC too warm, don’t even cool off after half an hour or more.

Craig's picture
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Craig Monday, 27 Dec 2021 at 5:46pm

Yep, bitten all over and itchy buggers! Yep was up the CC on the weekend, even hotter than Sydney. Was sweating Sat AM with the lack of wind and glassy surf.