The heat is gone
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.
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.
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.
I like the look of that tasty hot patch off the North Island.
not that hot, but hot enough.
Still 26-27 degrees in close here.
Yeah the EAC is still good north of Port..
Where’d you locate that chart Craig ?
Nice work Craig, love these articles.
Now I've got Glenn Frey going round in my head.
the heat is gone, on the greet
with Eddie Murphy bouncing around in the back of a B Double with contraband ciggies!
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?”
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.
Yeah the amount of varying factors, teleconnections between ocean basins across thousands of kilometres and upper atmospheric influence is endless but also fascinating.
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
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.
Unfortunately yes it does (wind regime wise) for coming 2-3 months.
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.
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?
plenty of time left.
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.
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..
And another one off Coffin Bay, stretching up to Elliston (17 degrees, whilst Cactus is 22!). Ahh, memories of icecream headaches in February...
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
Zero cyclone swells in the north west crrates saltwater wells in my eyes.
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 .
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.
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
I would pay to have the song out of my head :)
Tell me, can you feel it?
Great article. Thanks.!