A look back on the La Niña summer of 20/21

Craig Brokensha picture
Craig Brokensha (Craig)
Swellnet Analysis

Rejoice can be heard from across the southern states as March 1st brings to a close one of the worst summers for surf in recent memory.

Of course this depends on which side of Port Phillip Bay you reside and who you talk to. Some claim that the beaches have been great fun, while others talk of the endless closeouts. One thing is true though, there's been nothing of note to the west. Since winter ended, I can't recall forecasting a large, clean run of solid groundswell for the Surf Coast reefs.

Luckily the drought was broken on the last day of summer with the arrival of a decent south-west groundswell arriving under light offshore winds, though it was only a one day wonder.

Below we have the last three months combined into two handy charts. The first shows the difference in Mean Sea Level Pressure for the summer months December, January, and February compared to the long term climate average (1981-2010).

Red indicates that the pressure was higher (positive) than the long term climate average during the summer period, while blue values show that the pressure was lower (negative).

Mean Sea Level Pressure anomaly for the months of December, January, February 20/21

What immediately stands out is the large high pressure anomaly stretching from under the Indian Ocean (south-west of Western Australia) across to Tasmania and then into the Tasman Sea.

While winds generally aren't favourable through summer for the southern states, and more often than not out of the south (onshore), what La Niña does is exacerbate this by shifting the sub tropical high pressure belt further south than normally seen through summer, putting a bigger block across the Southern Ocean engine room.

The position of the positive anomaly further south across the Roaring Forties shows that the highs were positioned further south than normal. With such a setup, polar fronts are steered closer to the ice shelf or are non-existent, producing a double whammy of minimal swell and onshore winds.

The reason for Western Australia's hot, windy weather can also be seen, that being a heat trough (low) running north-south along the coast, squeezing against the sub-tropical high to the south, pumping in heat from central Australia while also bringing strong coastal winds.

These winds at times met quality groundswells, more so through the end of January and February, but for the most part it was windy and small.

The flow on effects of such strong offshore winds was a less pronounced sea breeze season which also lead to less upwelling and a marine heat wave off WA's North West mid-late January.

The development of a tropical low off the North West early February converted this surface heat energy to torrential rain and flooding, while also reducing the ocean surface temperature.

Moving to the other side of the country, and the synoptic setup responsible for the great, consistent run of summer surf can be seen. That being lower pressure in the Coral Sea sitting atop the cradling high pressure belt stretching from the southern Tasman Sea to the south-east of New Zealand. This aimed fairly persistent easterly trade-winds towards the East Coast along with a couple of deeper intensifications, most notably a coastal trough in mid-December and Tropical Cyclone Lucas in early February. A final tropical low also pushed south through the Tasman Sea last week.

The chart that shows the swell generating engine best is the mean vector winds for the summer months (see chart below). These are the average overall winds throughout December, January, and February - not the anomaly (which is the difference from normal).

Mean winds through the months of December, January, February 20/21

During this period, a broad swathe of easterly trades were positioned between New Zealand and New Caledonia. While looking across to Western Australia we can also see the strong, persistent south-east winds.

One noticeable positive from the setup across the East Coast was winds from the south-eastern quadrant which reduced upwelling, keeping inshore water temperatures toasty which in turn inhibited the development of afternoon sea breezes. This provided plenty of great afternoon and evening sessions, especially across southern NSW.

If we had upwelling, the temperature differential from the heating land during the day and cooler waters would have brought in stronger sea breezes. The extra cloud cover also associated with La Niña also prevented land temperatures reaching any great heights, with Australia recording it's coolest summer in nine years.

Tasmania faired really well through the summer, with the East Coast seeing plenty of localised north-easterly swells mixed in with stronger, less consistent east-northeast swells from the tropical activity.

The South Arm managed to pick up persistent small waves from whatever polar frontal activity there was though with plenty of winds from the north-east direction to keep conditions clean.

Looking at the coming autumn, La Niña is weakening and we're due to see a run of southerly swell for the East Coast over the coming week, with the tropical wave of activity (MJO) not forecast to be back in our region until at least the second half of March, if that.

So it looks like we're in limbo for now, though keep an eye on the regional Forecaster Notes for more detailed and up to date rundown.

Comments

vbaaccess's picture
vbaaccess's picture
vbaaccess Wednesday, 3 Mar 2021 at 8:45am

Great written explanation with science backed evidence.

freeride76's picture
freeride76's picture
freeride76 Wednesday, 3 Mar 2021 at 10:03am

Nice one Craig .

CMC's picture
CMC's picture
CMC Wednesday, 3 Mar 2021 at 10:25am

Thanks Craig
Just out of curiosity, do you know sort of wet season Indo had while we had this La Nina?

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming Wednesday, 3 Mar 2021 at 7:05pm

Judging from what ive seen on social media looked pretty decent, fair bit of swell.

Craig's picture
Craig's picture
Craig Thursday, 4 Mar 2021 at 9:10am

Looks like from Java further east to Bali and beyond it's been a wetter than normal wet season.

Here's the precipitable water anomaly for the last 3 months, red = wetter.

CMC's picture
CMC's picture
CMC Thursday, 4 Mar 2021 at 9:43am

Thanks for that Craig
Interesting to note they've also had wetter than normal also.
Still would have been plenty of good waves working as always in Indo.
Cheers

wiseautogas's picture
wiseautogas's picture
wiseautogas Wednesday, 3 Mar 2021 at 10:36am

have to admit makes sense surfing 44 years in sa this would have to have been the worst summer bar the beginning i can remember

vicbloke's picture
vicbloke's picture
vicbloke Wednesday, 3 Mar 2021 at 2:56pm

hearing you wise. been surfing the Surf Coast since early 80s and the last 8 months or so would have to be the worst i can remember. hopefully autumn will see a change of luck

deanw12's picture
deanw12's picture
deanw12 Thursday, 4 Mar 2021 at 8:57am

No argument there, definitely the most surfless period I have ever seen in 50 years, mainly just howling southerlies and not much swell.

Itsmemickyb's picture
Itsmemickyb's picture
Itsmemickyb Sunday, 7 Mar 2021 at 8:43am

taranaki was the same, mostly small weak swells

blackers's picture
blackers's picture
blackers Wednesday, 3 Mar 2021 at 11:19am

Cheers Craig, nice explanation.

dr-surf's picture
dr-surf's picture
dr-surf Wednesday, 3 Mar 2021 at 2:08pm

So who’ had the Best waves during this La Niña? GC, Byron to Ballina, Central Coast or South Coast.

adsi's picture
adsi's picture
adsi Friday, 5 Mar 2021 at 7:54pm

I'd say gold coast. I live in lennox and although there have been plenty of good and fun days, most of the big swells just maxed out around here and theres not much to surf. Today was fun as f##k though

bbbird's picture
bbbird's picture
bbbird Wednesday, 3 Mar 2021 at 5:35pm

Best waves are where you find them.

Justonemore's picture
Justonemore's picture
Justonemore Wednesday, 3 Mar 2021 at 6:38pm

Slow phone all good

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming Wednesday, 3 Mar 2021 at 7:19pm

Not the best summer but also not the worst, not a lot of NE off shores, so not a lot of hot weather, but there has been a decent amount of swell, the downside of a decent amount of swell and not a lot of offshores is banks have been average or just not a lot of banks, which isn't good for crowds.

Redmond Clement's picture
Redmond Clement's picture
Redmond Clement Wednesday, 3 Mar 2021 at 9:10pm

My thoughts and prayers are with the Victorians.

tango's picture
tango's picture
tango Thursday, 4 Mar 2021 at 8:16am

Thank you, Redmond. As are the Victorians'.

There's been a few little diamonds in the rough, but as said earlier, the last 8 months have been well below par.

Good article, Craig, thanks.

geek's picture
geek's picture
geek Thursday, 4 Mar 2021 at 9:36am

*Below par for the surf coast.

Up until the start of December I would say 2020 was the best year on the MP in at least 7 years. Only had to surf WP a few times! Summer been a shocker though

nasigoreng's picture
nasigoreng's picture
nasigoreng Wednesday, 3 Mar 2021 at 11:34pm

Total days with a temperature of 30 degrees+ at Aireys Inlet VIC this summer:

December = 1 day
January = 1 day
February = 2 days

Shit surf, winds and weather. Hmmmmmm............. overpriced beach houses?

http://www.bom.gov.au/climate/dwo/IDCJDW3001.latest.shtml

surfstarved's picture
surfstarved's picture
surfstarved Thursday, 4 Mar 2021 at 12:01pm

Yes it's been a completely shit summer for surf, but there have been a couple of positives.
1. It's been a way cooler summer thanks to the incessant southerlies. I struggle when it gets over 35 here in SA, when the whole world feels like it's a giant oven. It's a white, radiant heat that leaches everything of colour and you just don't want to be outside until the last hour before sunset.
2. Summer northerlies (offshore at my local) are usually associated with 40+ days, which often bring with them strong SW changes and highly elevated bushfire risk. Yes it's great to get in the water, but no fun if your community is under threat from an inferno.

I'd love more time in the water over summer, but if it means I have to go through what we experienced in Dec. 2019 again, then I'll gladly wait until winter when the swells are more solid and the crowds thinner.

Ash's picture
Ash's picture
Ash Friday, 5 Mar 2021 at 12:55pm

I do concur Surfstarved, I'm glad we got through Jan and Feb with minimum 40C + days, happy it's March. But we're still not out of the SE curse yet, next week looks like the last 3 weeks, everyday is onshore.
I don't mind working but I'm looking forward to downing the tools for a surf, If I can remember how....

oiley's picture
oiley's picture
oiley Thursday, 4 Mar 2021 at 2:40pm

Yep Tullamarine has had the best conditions this summer

spt's picture
spt's picture
spt Thursday, 4 Mar 2021 at 9:06pm

I've heard it's always offshore in Tulla! Is that true???????

Puzzled's picture
Puzzled's picture
Puzzled Saturday, 6 Mar 2021 at 1:19pm

No. Onshore in a strongish southerly but take off area is protected then crumbles down the line with the breeze.

Howie66's picture
Howie66's picture
Howie66 Sunday, 7 Mar 2021 at 10:11am

I still don’t know why they didn’t build it the other way around! So SE would be offshore. Would’ve almost have been offshore everyday this summer

mac396's picture
mac396's picture
mac396 Thursday, 1 Apr 2021 at 7:21am

A very late comment here but not only did we have consistent NE swells most of summer here in Tassie but also some big SSW and S swells getting into our point breaks down here on the South Arm and up the East coastr. Unusual during summer?