The heat is gone

Craig Brokensha
Swellnet Analysis

Since December, the Madden Julian Oscillation (MJO) has passed through the Coral Sea twice on its circuit of the globe.

With each pass, the MJO has brought increased moisture, triggered by tropical instability, which is great news for Queensland and northern NSW surfers as those disturbances and storms are the source of their easterly swell - and this season they've received a lot.

Now, satellite observations of the Coral Sea and Western Pacific are showing up interesting sea surface temperatures and it's all linked to the recent tropical activity.

You see, atmospheric instability is only one of the precursors necessary for tropical storms of strength. Another is warm sea surface temperatures.

During La Niña years we see warm water piling up in the Western Pacific Ocean, filtering down into the Coral Sea. The warmer water provides more moisture and heat for the atmosphere to feed off, which, as mentioned, leads to increased convection (storms) and tropical cyclones when the setup is prime.

Once these depressions start to deepen, they feed off the surface sea temperatures, extracting energy as they do so.

The latent heat flux (transition) from ocean to atmosphere is the key driver for tropical cyclones and storms.

All things being equal, if energy is extracted from the sea surface, we see the water temperatures dropping. This is the reason why tropical cyclones need sea surface temperatures of 26.5 or more to maintain their strength. Any lower and there's not enough energy to continually power the cyclone, hence they break down once moving into cooler waters or over land (no water).

If we have a quick look at the sea surface temperature charts from just before the tropical activity kicked off (start of December) to now (February) one can see a fair bit of energy used up in the way of a drop in temperature across selected areas to our east. Marine heat waves are also shown, that being short periods of abnormally high temperatures.

Sea Surface Temperature Anomaly chart for December 1, 2020

Sea Surface Temperature Anomaly chart for February 9, 2021

This exchange of energy is best viewed on the sea surface temperature anomaly charts (difference of temperature compared to the long-term climate average). At the state of December, most of the Coral Sea and Western Pacific were 1-2 degrees warmer than normal. The equatorial upwelling that is the classic La Niña signal (cold water) can also be clearly seen along the equator.

Switching to now and we can see that there's been some cooling, most noticeably south of New Caledonia and in the immediate vicinity of Fiji and to its south.

The coldest areas appear to the south of Fiji and if we look at the recent evolution of tropical lows and cyclones over the past two months, that's the area in which they've strengthened and tracked.

Below is an overlay of the tropical storms on top of February's sea surface temperature anomaly chart and you can see the blue patches matching up with where the storms that formed between Vanuatu and Fiji tracked. That being south-southeast of Fiji. This included Tropical Cyclones Ana and Bina near Fiji and then Lucas which moved south across New Caledonia before turning extra-tropical, producing that blue patch in the central Coral Sea. Keen observers will notice the cooler temperatures around the Sydney region from the weekend's north-east upwelling event and also the upwelling off South Australia's South East from strong, persistent south-east winds.

Storm tracks overlaid on top of the current Sea Surface Temperature Anomalies

We've ran similar articles in the past showing cyclone signatures of Pam (2015) and most impressive Yasi (2011) which is well worth a read. Yasi was such a significant, category 5 cyclone that by itself it dropped surface temperatures by some 4 degrees.

The MJO is forecast to remain across the Western Pacific Ocean over the coming one-two weeks which is positive for continued easterly swell energy, but follow the regional Forecaster Notes for more in depth analysis. 

Comments

freeride76's picture
freeride76's picture
freeride76 commented Thursday, 11 Feb 2021 at 4:18pm

I like the look of that tasty hot patch off the North Island.

not that hot, but hot enough.

Blowin's picture
Blowin's picture
Blowin commented Thursday, 11 Feb 2021 at 4:27pm

Still 26-27 degrees in close here.

Craig's picture
Craig's picture
Craig commented Thursday, 11 Feb 2021 at 4:36pm

Yeah the EAC is still good north of Port..

Blowin's picture
Blowin's picture
Blowin commented Thursday, 11 Feb 2021 at 4:55pm

Where’d you locate that chart Craig ?

Sprout's picture
Sprout's picture
Sprout commented Thursday, 11 Feb 2021 at 5:00pm
Blowin's picture
Blowin's picture
Blowin commented Thursday, 11 Feb 2021 at 5:08pm

Unreal. Thanks

Sprout's picture
Sprout's picture
Sprout commented Thursday, 11 Feb 2021 at 4:58pm

Nice work Craig, love these articles.

thermalben's picture
thermalben's picture
thermalben commented Thursday, 11 Feb 2021 at 6:13pm

Now I've got Glenn Frey going round in my head.

dawnperiscope's picture
dawnperiscope's picture
dawnperiscope commented Friday, 12 Feb 2021 at 12:03pm

the heat is gone, on the greet

Ride on

ringmaster's picture
ringmaster's picture
ringmaster commented Monday, 15 Feb 2021 at 3:10pm

with Eddie Murphy bouncing around in the back of a B Double with contraband ciggies!

Blowin's picture
Blowin's picture
Blowin commented Monday, 15 Feb 2021 at 3:49pm

I watched it the night Ben put it up here. Cant stop playing it in my head either.

“ You’re not going to fall for the old banana in the tail pipe trick?”

crg's picture
crg's picture
crg commented Thursday, 11 Feb 2021 at 7:18pm

Nice reading again Craig...thanks for the info...never ceases to amaze me how all these weather and ocean patterns combine to give us good waves. Makes it all the more special or perhaps appreciative when you get a good one knowing what goes into making it happen.

I'm not cheap,
But I'm free.

Craig's picture
Craig's picture
Craig commented Monday, 15 Feb 2021 at 2:09pm

Yeah the amount of varying factors, teleconnections between ocean basins across thousands of kilometres and upper atmospheric influence is endless but also fascinating.

Major kong's picture
Major kong's picture
Major kong commented Thursday, 11 Feb 2021 at 7:26pm

yeah i really dig these articles too. cheers for getting into the nitty gritty. enjoy the waves east coasters, our time ( south ) will come. yin and yang

Major kong

hpat's picture
hpat's picture
hpat commented Thursday, 11 Feb 2021 at 7:32pm

what does this mean for vicco? does it affect us? more shitty easterlies for the forseeable future? or could we start to see some sw groundswells coming within the next few months? cheers for these write ups btw they're heaps interesting.

Craig's picture
Craig's picture
Craig commented Monday, 15 Feb 2021 at 2:07pm

Unfortunately yes it does (wind regime wise) for coming 2-3 months.

Dx3's picture
Dx3's picture
Dx3 commented Monday, 15 Feb 2021 at 3:20pm

This is the worst news I've read in a long time. And coming from a Victorian in his 3rd lockdown...that says a lot.

hpat's picture
hpat's picture
hpat commented Monday, 15 Feb 2021 at 5:56pm

fark :')

Distracted's picture
Distracted's picture
Distracted commented Thursday, 11 Feb 2021 at 7:57pm

That is really cool Craig. Can see why cyclones can have a positive impact on the Barrier Reef, mixing in some cool water that reduces coral bleaching.
So does the cooler sea temperatures mean that La Niña and any cyclones are over for the season, or is there still time for the Coral Sea to warm back up and kick out some more tropical weather our way?

freeride76's picture
freeride76's picture
freeride76 commented Thursday, 11 Feb 2021 at 8:40pm

plenty of time left.

Spuddups's picture
Spuddups's picture
Spuddups commented Friday, 12 Feb 2021 at 6:21am

From my understanding tropical cyclones are rare in the vicinity of Tahiti. I wonder if they might get one this year due to that marine heatwave.

Craig's picture
Craig's picture
Craig commented Friday, 12 Feb 2021 at 7:43am

For those in South Australia, check out the Bonney upwelling system, off the South East.

This is from strong south-east winds through the summer, moving surface water to the left (offshore) and then being replaced by cold, nutrient rich water off the shelf. Great for primary production but not for surfing..

thermalben's picture
thermalben's picture
thermalben commented Friday, 12 Feb 2021 at 7:56am

And another one off Coffin Bay, stretching up to Elliston (17 degrees, whilst Cactus is 22!). Ahh, memories of icecream headaches in February...

cutty1957's picture
cutty1957's picture
cutty1957 commented Friday, 12 Feb 2021 at 2:00pm

Thanks, Craig for the excellent information on T.C"s. I spent 12 years teaching geography at Gisborne Girls High in NZ (before I moved to Torquay) and my students always struggled with the process of latent heat as a driver for these storms. Your explanation is the best I have seen...... cheers

Redmond Clement's picture
Redmond Clement's picture
Redmond Clement commented Friday, 12 Feb 2021 at 8:39pm

Zero cyclone swells in the north west crrates saltwater wells in my eyes.

PCS PeterPan's picture
PCS PeterPan's picture
PCS PeterPan commented Monday, 15 Feb 2021 at 1:59pm

I would pay to sit and have some of this meteorological complexity explained to me. Thanks Craig , your knowledge and way of explaining it to punters such as myself are always appreciated .

Craig's picture
Craig's picture
Craig commented Monday, 15 Feb 2021 at 2:03pm

Thanks PCS, Cutty, Distracted and others for the kind words. As most of you know I love trying to break down these complex meteorological/oceanographic happenings into layman's terms.

Sheepdog's picture
Sheepdog's picture
Sheepdog commented Tuesday, 16 Feb 2021 at 1:09pm

Howdy mate, long time no chat. Your comment re upwelling (south east and east winds) being great for primary production but not for surfing. Spoken like a true natural footer ;) It aint all about Bells and the surf coast u know :p

Sheepdog

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno commented Monday, 15 Feb 2021 at 4:09pm

I would pay to have the song out of my head :)
Tell me, can you feel it?

Bruce Kay's picture
Bruce Kay's picture
Bruce Kay commented Wednesday, 17 Feb 2021 at 5:22pm

Great article. Thanks.!