Not so dry July

Craig Brokensha
Swellnet Analysis

Fresh monthly data has come in regarding the synoptic setup across our various swell generating basins, from the Indian Ocean through to the South Pacific, and it paints a pretty clear picture.

I don't plan on doing these analysis articles monthly, but when the data is interesting to look and talk about I'll delve into it.

During June we saw a low pressure anomaly south of the Bight bringing lots of westerly energy with clean conditions for South Australia and Victoria, while a strong high sitting just behind New Zealand provided plenty of fun sized energy out of the east.

Looking at last month, July, Indonesia continued to pump as the same swells that impacted Western Australia travelled north. WA itself generally saw clean conditions north of an imaginary line drawn just below Mandurah, while to the south it was mostly onshore. Victoria's Surf Coast failed to see any significant swell at all though conditions were good to great for the more open beaches.

Tasmania's South Arm remained small to tiny for most of the month, while the East Coast saw plenty of activity owing to the clustering of low pressure systems through the Tasman Sea. These same lows generated significant back to back swell events for southern NSW, with less size but great waves further north and into Queensland.

Having a quick glance at the Mean Sea Level Pressure anomaly charts (difference from the climate average) we can see a strong and broad low in the Indian Ocean, a north-west to south-east aligned high across southern Australia and then a dip through the Tasman Sea.

Mean Sea Level Pressue Anomaly for July

The reason for the strong anomaly in the Indian Ocean is due to the polar jet being driven north just ahead of (read east of) the MJO, which has been near stationary between 60-100E and off eastern Africa.

This has brought the endless run of swells for Indonesia and Western Australia, while the positioning of the high has directed winds more from the northern quadrant across that state.

What is also apparent is the blocking influence of the high pressure anomaly across the southern states, leading to the run of poor waves on the Surf Coast but out of season and fun surf across the more exposed breaks. South Australia has seen similar favourable conditions with smaller swells.

Not much has to be said about the East Coast. Southern NSW has had one of the better winters in the last decade with the supporting ridge of high pressure from Tasmania to New Zealand, cradling lows as they developed in the Tasman Sea.

When looking at the mean (not anomaly) jet stream, that being the winds through the upper atmosphere at around 500mb, we can see that there is a split across eastern Australia and the Tasman Sea. This occurs when the jet stream encounters a blocking pattern, and this can be seen at the surface in the anomaly across central and southern Australia in the image above.

Split in the jet stream (hole across the southern Tasman Sea) eveident in the mean 500mb winds for July

With a split in the jet stream like that shown, multiple storms can form in the same spot due to the almost static air aloft. Sound familiar? This is one of the reasons behind the clustering of lows and storms off the East Coast.

Looking ahead and the European Centre for Medium Range Forecasting (ECMWF) has higher than normal pressure forecast under Australia and across to New Zealand through August, with a low pressure dip off the NSW coast, slowly weakening into September though still there. This would likely result in a continuation of average conditions for the Victorian Surf Coast and plenty more swell for the the East Coast.

We'll continue to monitor what is shaping up to be quite a year of weather watching.

Comments

tango's picture
tango's picture
tango commented Wednesday, 5 Aug 2020 at 10:25am

Good work, Craig. Such a shame there can't be consistent good days on all coasts...instead of robbing Peter to pay Paul.

The other thing to note has been the glassy days through June/July in Vic. In a normal year it would be rare to get a single glassy day, even consistent very light winds, more than twice a month but it's been like Indo in a steamer sometimes more than twice a week.

radiationrules's picture
radiationrules's picture
radiationrules commented Wednesday, 5 Aug 2020 at 10:46am

Hi Craig > excuse my ignorance but is this statement, something I can see on one of those maps above: "The reason for the strong anomaly in the Indian Ocean is due to the polar jet being driven north just ahead of (read east of) the MJO, which has been near stationary between 60-100E and off eastern Africa.

This has brought the endless run of swells for Indonesia and Western Australia, while the positioning of the high has directed winds more from the northern quadrant across that state."

RR

Craig's picture
Craig's picture
Craig commented Wednesday, 5 Aug 2020 at 10:55am

So this insight was gleaned from my good mate Tyson when trying to identify the reason for the anomaly in the south-west Indian Ocean.

The MJO was stationary across eastern Africa, and the polar jet was brought north and into the Indian Ocean (ahead of it), hence bringing strong polar storms up into the mid-latitudes, causing that purple anomaly.

Here's the MJO identified by looking at the outgoing longwave radiation (negative blue), sitting between 20-100E for all of August (it's now on the move east).

radiationrules's picture
radiationrules's picture
radiationrules commented Wednesday, 5 Aug 2020 at 6:55pm

Thanks Craig - although I do feel like BB King must have felt like when Bono handed him sheet music, to which he said "I can't read music, I just play what I feel". In other words, I'm a still unable to understand what you say, as you have so much assumed knowledge and I'm a bit dyslexic, which doesn't help. eg MJO?

I've heard it said in NW WA and in Indo (Kandui resort owner) and others online - that this winter is a "once in a ten year event". I assume they mean the multiple back-to-back swells - because the pattern itself is atypical to me - across swell direction, swell size and wind direction - other than the northerly blows on top of typical SW/SE patterns.

So net question: is this years pattern, significantly different to the last 10 years? thanks fro your considered viewpoint - I'm always hoping to learn more.

Craig's picture
Craig's picture
Craig commented Wednesday, 5 Aug 2020 at 7:41pm

Ah sorry, yes the MJO is the Madden Julian Oscillation and is effectively a wave of enhanced tropical activity that circles the globe. A bit more info here.. https://www.swellnet.com/news/swellnet-analysis/2018/01/23/mjo-rising

In our summer when across our region and amplified it brings increased rainfall, convection and cyclone activity. Same happens during our winter, though influencing the tropical Northern Hemisphere.

We've seen the MJO stationary around eastern Africa through all of July, and with this, the polar jet stream which steers surface cold fronts and weather has been more pronounced and focussed up into the Indian Ocean.

Re that 10 year thing, not quite sure sorry.

radiationrules's picture
radiationrules's picture
radiationrules commented Thursday, 6 Aug 2020 at 9:48am

Hi Craig > many thanks for all of that extra information, which I'll study. Plenty to lean from you & Ben. > RR

Craig's picture
Craig's picture
Craig commented Thursday, 6 Aug 2020 at 11:24am

Also this stalling of the MJO across eastern Africa has resulted in the lack of typhoons in the Pacific..

From the Bureau of Meteorology

"For the first time since at least 1949, no named storms (i.e. equivalent to a category 1 or stronger Australian tropical cyclone) developed in the western North Pacific basin in July 2020. In a typical year, this region sees between 3 and 4 tropical cyclones in July. This continues the well below-average tropical cyclone activity in the western North Pacific Ocean this year. Only one typhoon (equivalent to a category 3 Australian tropical cyclone) had been observed to the end of July 2020, compared to the long-term average of about 5."

Queef Jerky's picture
Queef Jerky's picture
Queef Jerky commented Thursday, 6 Aug 2020 at 9:07pm

I thought that pattern usually moves around the globe? Any idea why it stalled there for 2 months?
Did the other southern continents get bunked?

P.S I think the little lines on the synoptic chart should keep being interesting, so we can learn from you every damn month!

vicbloke's picture
vicbloke's picture
vicbloke commented Wednesday, 5 Aug 2020 at 10:55am

correct Tango. Surf Coast has been glassy but real lack of swell in July. Probably worst July in 10 years from memory.

brainiac's picture
brainiac's picture
brainiac commented Wednesday, 5 Aug 2020 at 6:47pm

longer than that i reckon Vicbloke , and June wasn't good either.

tango's picture
tango's picture
tango commented Wednesday, 5 Aug 2020 at 8:00pm

Agreed....I've been down here 17 years (only 13 more and I'm local) and it's the worst I've seen. Mind you, I'm ok if it wants to stay glassy but be a consistent 4-6ft.

vicbloke's picture
vicbloke's picture
vicbloke commented Wednesday, 5 Aug 2020 at 8:12pm

seemed to have surfed 13th more than normal this winter. more northerlies and less westerlies makes for smaller surf I guess

drchris's picture
drchris's picture
drchris commented Saturday, 8 Aug 2020 at 10:20am

Tango, I've been down here for 32. its the worst run I remember. Those glassy sessions are devilish and mask the real issue, the blocking high. Seeing the northern lows come down to this latitude since 2000s was the first sign for me that climate change was changing. having these strong SEs so regularly this year so unusual and I can't recall a July and august like this one. on a positive, been amazing for the beginners and a blessing for the kids stuck at homeschool

tango's picture
tango's picture
tango commented Saturday, 8 Aug 2020 at 1:38pm

Well, DrC, at 32 you've got your stripes. Now I know that I will try and defer more in the water....!

drchris's picture
drchris's picture
drchris commented Saturday, 8 Aug 2020 at 5:38pm

Mr T, you surf so smoothly, with flow and flex like no other, it is I that will always defer to your good self squire.

redclement.'s picture
redclement.'s picture
redclement. commented Wednesday, 5 Aug 2020 at 1:37pm

Great to see some decent inland rain.

Halfscousehalfcockneyfullaussie's picture
Halfscousehalfcockneyfullaussie's picture
Halfscousehalfc... commented Wednesday, 5 Aug 2020 at 7:15pm

Great article, this is why swellnet shits on the others

Craig's picture
Craig's picture
Craig commented Wednesday, 5 Aug 2020 at 7:43pm

Thanks Halfs.

Yendor's picture
Yendor's picture
Yendor commented Thursday, 6 Aug 2020 at 6:04am

Thanks Craig, this really helps explain some of the 'why' of the clustering from the last article. Such a complicated set of factors playing into the trends of weather systems and hence swell patterns.
Pretty amazing that people such as yourself are getting a handle on these things now and how they affect the surf longer term.

Craig's picture
Craig's picture
Craig commented Thursday, 6 Aug 2020 at 7:00am

Thanks Yendor, love learning more and more along with the discoveries and teleconnections scientists are finding between certain climate drivers.

And re your question in the other article re El Nino and La Nina for New Zealand, as Island Bay answered, under El Nino New Zealand cops more fronts and weather from the west to south-west.

Yendor's picture
Yendor's picture
Yendor commented Friday, 7 Aug 2020 at 8:43am

Cheers Craig, pretty familiar with those El Niño westerlies living in Wellington. Spring time and El Niño can be a pretty hellish combination, hard to get out the door without being blown away sometimes.

memlasurf's picture
memlasurf's picture
memlasurf commented Thursday, 6 Aug 2020 at 4:25pm

So Craig more great surf for the east coast (Melbourne), and I can sneak out the back to get a wave even in Covid Lock Down. Excellent conditions and no people life is exceedingly good at present (sorry for the rest of you who can't participate, but hey I have spent most of my life down here so fuck it time to cash in).

Finn Gunther's picture
Finn Gunther's picture
Finn Gunther commented Friday, 7 Aug 2020 at 3:51am

June/July was absolutely horrible for the surf coast!

:)

drchris's picture
drchris's picture
drchris commented Saturday, 8 Aug 2020 at 10:26am

really interesting read Craig. its an unusual time. the Cape Otway average for winter is attached.

http://www.bom.gov.au/climate/averages/climatology/windroses/wr09/wrpdf/...

calm 2% time, get the odd easterly pattern. still, I think in 30 odd years, this is the most bizarre winter on the surf coast . So many incredibly glassy days. great for the beginners and kids stuck at home school

Pngy's picture
Pngy's picture
Pngy commented Sunday, 9 Aug 2020 at 10:32am

So good Craig, love this analysis! Surf has been non-stop in SA, but bummer for the Viccos at the Surf Coast