Shivering in Sumatra

Craig Brokensha
Swellnet Analysis

A few years ago we introduced you to the Indian Ocean Dipole (IOD), an index monitoring the difference in water temperature across the Indian Ocean Basin. The talking point was a strong positive event in 2015, bringing poor and strong S/SE winds to the Mentawais while providing an excellent late season in the Maldives owing to the persistent sizey south-east swell.

Another positive IOD event has occurred this year, but the strength is almost twice that of 2015, and reports coming back from the Sumatran region are of cold water, very strong and limiting S/SE winds along with much drier weather.

This from a regular Swellnet contributor on the ground..

“Everyone is a bit stunned by the water temps. Apparently they are way down on normal. About five weeks ago was meant to be even colder. With a plague of stinging jellyfish. When I first got here three weeks ago I was forced out of the water from wind chill with the long waits between sets. Many long term visitors reckon its unprecedented .

I saw a local Indo fella in his diving steamer and hood the other day, but that was an aberration, most crew are just in neoprene vests. I’m just right in a spring suit. Luckily I met a bloke who was leaving who sold me a spring suit.

I reckon the water is 21-22 but the wind makes it seem colder if you’re sitting around for a while.

The water has been green mostly and then brown with the big swells. Lots of foam on the water and thick fogs due to temperature differences.

Every day has strong SSE winds, which are supposed to be dying or glassy this time of year.

Locals are saying it’s very much drier than normal as well. Should be rains most nights but have only had one or two brief showers.

Swells have been relentless though. Everyone is saying they’ve never seen such a prolonged run of large swell , particularly this time of year. The point here has been 6-8 plus ( plus, plus ) for a week or so.”

So what's the cause and how significant is this year's event?

The Indian Ocean Dipole is a measure of the difference in water temperature between the north-western Indian Ocean (off the African coast) and north-eastern Indian Ocean (off Indonesia).

In a positive phase, the waters off Indonesia and northern Western Australia are colder, with warmer water off the African coast, and opposite under a negative phase. This plays a big part in Australia's climate as well as affecting the winds and weather across the Indian Ocean basin.

Sea Surface Temperatures 4deg+ colder than normal off Sumatra late October

When in a positive phase, (with colder waters off north-west Australia) there's less moisture available to weather systems pushing down and across Australia, resulting in a drier and hotter weather through winter and spring. When negative, the warmer waters off Australia bring increased rainfall to the country and lower maximum temperatures.

The triggers for IOD events are still unknown, some believe they are triggered from the western Pacific Ocean and linked to El Nino/La Nina events but others believe it is triggered closer to Indonesia.

When looking at positive events like we're in now, an initial upwelling event off the Sumatran coast at the start of winter results in a greater heat differential between the ocean and land, and stronger sea breezes out of the S/SE, which then again creating more upwelling and a positive feedback loop.

Equatorial westerly winds also weaken and even reverse, pilling up warmer water to the east towards Africa and enhancing the upwelling further off Indonesia. Similar to upwelling events off the Australian coast, the increase in nutrients and photosynthesis has also resulted in darker, greener waters which can be picked up by satellite by looking at the chlorophyll concentration.

Chlorophyll Concentration observed by satellite identifying upwelling off Indonesia

This year's event has seen the IOD index push just over 2, (2.06 to be exact) and this is the strongest since 1997, some two decades ago, and likely the second strongest in the last 37 years of records.

IOD Index showing current event pushing above 2 and the last 37 years of historical data

This years event was strong early on but continued to strengthen the last two months and is now peaking.

Satellite observations show the evolution of the upwelling event and we can also see that sea surface temperatures off South Sumatra have dropped over 4 degrees from normal. Add this drop in temperature with long waits between sets and strong S/SE winds and it makes for a much colder than normal Indonesia surf trip. It's also limited surfing options in between swell events, with the usually reliable southerly swell magnets blown out. There have been more than a few reports of people getting skunked on their Indo trips this year.

Evolution of IOD event with cold water upwelling off Indonesia. Animation shows April through October

Looking at the wind anomalies (difference from climate average) for the Sumatran and Mentawai region you can clearly see S/SE winds have been stronger than normal, identified by the long drawn out arrows.

Wind and Sea Surface Temperature anomalies for the month of August

Some may wonder if this strong positive IOD event is linked to the Sudden Stratospheric Warming event, and in short no it isn't but this later phenomena is likely linked to the extended run of large swell late season.

IOD events usually weaken and break down through spring and don't influence the summer months across Australia, but because of the strength of this current event, it's likely to linger into the start of Summer, keeping Australia hotter and drier than average and the winds blowing across Sumatra and the Mentawais.

Comments

freeride76's picture
freeride76's picture
freeride76 commented Thursday, 31 Oct 2019 at 2:24pm

did the Maldives benefit from the increased SE trade flow across the eastern Indian Ocean?

Craig's picture
Craig's picture
Craig commented Thursday, 31 Oct 2019 at 2:26pm

Heard that it's been another good season of swell, but locally winds there have messed with a few spots.

mibs-oner's picture
mibs-oner's picture
mibs-oner commented Thursday, 31 Oct 2019 at 9:50pm

Seen a vid of vodi pumping the other day

simba's picture
simba's picture
simba commented Thursday, 31 Oct 2019 at 2:36pm

Sounds like Blowins gone under cover in deep dark indo..........?

simba

Waldorf Salad's picture
Waldorf Salad's picture
Waldorf Salad commented Thursday, 31 Oct 2019 at 2:51pm

Climate change! Rruuunnnn!!!

stephen.allen's picture
stephen.allen's picture
stephen.allen commented Friday, 1 Nov 2019 at 1:30pm

Where toooo?

derra83's picture
derra83's picture
derra83 commented Thursday, 31 Oct 2019 at 3:01pm

It's hard to tell from that pixelated map but it seems there;'s also cold water at Bali and east Indo. I wonder if there's any connection with that and the recent white shark sightings.

Craig's picture
Craig's picture
Craig commented Thursday, 31 Oct 2019 at 3:05pm

A bit more detail here..

Island Bay's picture
Island Bay's picture
Island Bay commented Thursday, 31 Oct 2019 at 3:01pm

So how did our intrepid reporter's new Desert Storm go?

udo's picture
udo's picture
udo commented Thursday, 31 Oct 2019 at 3:14pm

Dunno but Nate Behls being going hard on his Napalm..fuck !

inoshishi sex

stunet's picture
stunet's picture
stunet commented Thursday, 31 Oct 2019 at 3:18pm

Pretty sure that was from a few years back.

udo's picture
udo's picture
udo commented Thursday, 31 Oct 2019 at 3:33pm

yes i wondered that..maybe late arvo in a springsuit on a Wacko pic is more recent.

inoshishi sex

stunet's picture
stunet's picture
stunet commented Thursday, 31 Oct 2019 at 3:33pm

Rock solid effort but. Worth a replay:

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

A post shared by WEBSTER Surfboards Australia (@webstersurfboards) on

Westofthelake's picture
Westofthelake's picture
Westofthelake commented Thursday, 31 Oct 2019 at 4:12pm

Unreal!

The MIDdleman.'s picture
The MIDdleman.'s picture
The MIDdleman. commented Friday, 1 Nov 2019 at 10:29pm

Holy crap what a barrel.
I'd given up on him twice.

Signature.

yahabo's picture
yahabo's picture
yahabo commented Thursday, 31 Oct 2019 at 4:00pm

Does this phenomena usually wax and wane between one year to the next or does it usually sustain over a few years in a row? I am hoping the former, as I have a big trip next year with 36 of my closest mates!!!! 50th birthday...

Craig's picture
Craig's picture
Craig commented Thursday, 31 Oct 2019 at 4:02pm

You can see from the time-series from 1982 up until now that it wax and wanes. Resets every summer.

donweather's picture
donweather's picture
donweather commented Monday, 4 Nov 2019 at 2:12pm

Resets every summer but I wouldn’t say it waxed and wanes from one year to the next. There’s not enough data in that chart to fully analyse IMO yearly trends.

Craig's picture
Craig's picture
Craig commented Monday, 4 Nov 2019 at 2:18pm

In that regard I meant it goes back and forwards, data looks like that, no?

donweather's picture
donweather's picture
donweather commented Monday, 4 Nov 2019 at 2:54pm

Not always in a yearly pattern. Least not in that zoomed in chart. Take a look at late season 2018 and compare that to this late season this year. Same (as in positive) positive IOD.

andosbf's picture
andosbf's picture
andosbf commented Thursday, 31 Oct 2019 at 8:10pm

Is everyone on tour your closest mates, like everyone you don't have to be polite.

jetson.rover's picture
jetson.rover's picture
jetson.rover commented Wednesday, 6 Nov 2019 at 4:36pm

You will be travelling in a pack of 37 surfers?
Oh my gaawd.
Even the Brazzos and Euros that love surfing in a pack don't hold a candle to that.
Where and when are you going so me and i'm sure many others know when to avoid the place like the plague at the time lol?

yahabo's picture
yahabo's picture
yahabo commented Wednesday, 6 Nov 2019 at 8:02am

April 2020. Tell your friends! :-)

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming commented Thursday, 31 Oct 2019 at 4:03pm

Good article, so what does it mean for next year?

Craig's picture
Craig's picture
Craig commented Thursday, 31 Oct 2019 at 4:06pm

No one can predict it yet.. Researchers are trying to identify the triggers, interesting times..

greyhound's picture
greyhound's picture
greyhound commented Thursday, 31 Oct 2019 at 5:49pm

36 of your closest mates...
how many have you got all up?

yahabo's picture
yahabo's picture
yahabo commented Thursday, 31 Oct 2019 at 8:31pm

36 is the lot. Some I met on tinder.

harry s's picture
harry s's picture
harry s commented Thursday, 31 Oct 2019 at 6:28pm

Been back from Bali about a week. I spent two weeks based mainly around Keramas. The water temp was warm as expected except the last day where while it was still warm there were patches of chilly water.

jezza64's picture
jezza64's picture
jezza64 commented Thursday, 31 Oct 2019 at 7:46pm

I commented in another thread, water was cold in Bali in September. From Vicco, I was wearing a long sleeve wettie vest after having to bail after an hour from my first surf at Balangan in a rashie. East Coast was warmer. Scored though. Stoked :)

NickT's picture
NickT's picture
NickT commented Thursday, 31 Oct 2019 at 8:35pm

Great article, really explains the science behind what has been an uncanny season. So glad my mate told me to bring a 2/2 steamer. lots of unsuspecting tourists were only surfing for 30 minutes before getting too cold and heading in a few months back. Articles like this make your website ahead of the rest in Australia keep up the good work guys

blackers's picture
blackers's picture
blackers commented Thursday, 31 Oct 2019 at 9:45pm

Also linked to current drought conditions in Eastern Aus? I heard a report that it had been identified as having a greater impact than the old El nino.

Craig's picture
Craig's picture
Craig commented Friday, 1 Nov 2019 at 7:10am

Yep for sure, one of the factors.

Bnkref's picture
Bnkref's picture
Bnkref commented Thursday, 31 Oct 2019 at 10:18pm

Bali felt a few degrees cooler than usual in July and August. Sumbawa pretty nice. G-land was freezing.

nicko74's picture
nicko74's picture
nicko74 commented Thursday, 31 Oct 2019 at 11:47pm

G land always seems a bit chilly once it starts getting over the 6 foot mark. And always seems chiller than Bali

udo's picture
udo's picture
udo commented Friday, 1 Nov 2019 at 7:07am

Be good to pick Mcabe or Doris brain on this i dont ever recall cold water stories from those early Indo days
Anyone see the pic/footage of Kerzy charging big Indo on a 5'4

inoshishi sex

Craig's picture
Craig's picture
Craig commented Friday, 1 Nov 2019 at 7:51am

Lots of people in comments on social media mentioning the swarms of jellyfish.

This is from the upwelling, I would say there would have been lots of Salps in the mix as well..?

thermalben's picture
thermalben's picture
thermalben commented Friday, 1 Nov 2019 at 8:19am

Looks like a predictive IOD time series.

memlasurf's picture
memlasurf's picture
memlasurf commented Friday, 1 Nov 2019 at 8:53am

I saw a guy drop his boardies on the beach and scrub his nuts one day in Bali. The little blighters can sting.

I focus's picture
I focus's picture
I focus commented Friday, 1 Nov 2019 at 9:22am

Great special agent Blowin has reported, but Blowin how about a run down about your trip FFS.

Not fussed about the truth either feel free to over story.

Squidy's picture
Squidy's picture
Squidy commented Friday, 1 Nov 2019 at 5:07pm

Just recently back from Simeulue, water was still warm (maybe slightly off) but had persistent South winds. Swells had plenty of morning sickness/bump although we also had plenty of thunder storms every night

mickseq's picture
mickseq's picture
mickseq commented Friday, 1 Nov 2019 at 7:25pm

Lombok was very dry a month ago when I was there, never seen it so dry, the water was cold but I didn't think it justified a spring suit. Last Dec was pretty bad in terms of wind, hoping that is not going to repeat when I fly back in 4 weeks.

Stu2d2's picture
Stu2d2's picture
Stu2d2 commented Friday, 1 Nov 2019 at 7:33pm

Any chance of adding the Maldives to your range of forecasts?

ken.vincent's picture
ken.vincent's picture
ken.vincent commented Friday, 1 Nov 2019 at 9:02pm

Yep in Bali Sept, and French guy paddling round in springsuit complaining of how cold the water was. Still ok for vest & boardies for a Victorian!.

orourke 210's picture
orourke 210's picture
orourke 210 commented Saturday, 2 Nov 2019 at 8:01am

I will be paying attention to this before I head back to Indo again.
The super strong trades this year were bunk.
Spent about a month in Nias. Southerly winds most days and early. Definitely the worst conditions I've ever seen there.
At least I wasn't on a boat trip in the Ments, with every boat cramming into the spots that can handle south wind.
Learn something new every year I guess.

Mishad's picture
Mishad's picture
Mishad commented Saturday, 2 Nov 2019 at 11:20am

Sept spent on the Bukit and was colder than normal. Watched guys paddle around in spring suits and more than a couple steamers (euros and brazzos at padang and ulus). I wore an old beaten long sleeve wetty top/vest for several weeks until it filled up with water like a balloon after an Outside corner wipeout, and cos it was tied to my boardies with a double knot, I couldn't rip it off still and was stuck trying to surface from down deep. Was pretty fucked and rattled me how something so innocuous could end up so serious. After that the water didn't seem so cold anymore and opted for boardies only as per usual.

the hairy man's picture
the hairy man's picture
the hairy man commented Saturday, 2 Nov 2019 at 12:16pm

Just returned from three weeks in South Sumatra and and that’s the coldest water in over 10 years. 2015 was refreshing in the tropical heat but this was Arctic. I can’t believe how many people had wetsuits with them in Indo!

Dawn sesh was bitter cold and the poor Indos were teeth chattering the whole time. The trade winds blew early and strong, chilling to the bone. Even the midday fri-session would see us shivering after two hours. Had to sit in the sun to warm up, something I never do...

The Sea Fog actually came with the massive swell. Each morning we’d squint at the horizon; “There be sea monsters out there,” as 15 foot sets loom out of the mist and reel down the reef. On the last day the swell dropped, the sky cleared and the water started to warm.

Spare a final thought for the poor Indos. It hasn’t rained for four months, the wells are running dry and they’re unable to plant their rice. Even the monkeys are coming out of the jungle looking for water. The data’s backing up what the scientists are screaming: the climate is changing

Craig's picture
Craig's picture
Craig commented Saturday, 2 Nov 2019 at 2:34pm

Thanks for all the updates and stories. All interesting and great reading!

southey's picture
southey's picture
southey commented Sunday, 3 Nov 2019 at 12:36am

One way of early prediction for the IOD is if a Strong Cyclone / Typhoon forms in the Bay of Bengal in May then its a fair chance it will trigger a Positive IOD .

Also of note was the cyclone that formed between India and Oman way north in the Arabian sea , its also stalled longer than most . But was pretty much out of season . Strange days indeed .

There is also a link of the IOD preceding an ENSO event in the opposite effect dleayed by about 15 mths . Forgotten more than i can remember on this topic after having stopped studying it for few years now .
SWA's recent hot spell and todays NW infeed in the SE is decent sign going forward of an end to this EC Drought though . Hopefully turning around come late Wet season .

" SA's Reserve Capacity "

c735293's picture
c735293's picture
c735293 commented Sunday, 3 Nov 2019 at 1:13am

Just got back from E of B. Definitely wrong and strong winds. Even in L. Worse was the number of tatts and tans - No idea but still paddling into danger. There was some heavy swell in places noideas were chesting into. Had to laugh - but i guess that's 21st century "surfing"

Mike

the hairy man's picture
the hairy man's picture
the hairy man commented Sunday, 3 Nov 2019 at 9:43am

Sama sama mate, watched one guy paddle out,catch a small one then cop 30+ on the head and disappear into the harbour. No idea the power of the ocean

wallpaper's picture
wallpaper's picture
wallpaper commented Sunday, 3 Nov 2019 at 9:11am

so if that's the calibre of the clientelle that already know where it is why the secrecy

c735293's picture
c735293's picture
c735293 commented Monday, 4 Nov 2019 at 10:23pm

Hey Wallpaper. I think you're a regular on the chats and I respect you for that. The places I'm going to have gone out of vogue - Thanks to the IOD, google maps and websites.
If it's just dudes out of their depth I'm watching get in trouble. I can't tell all of them to go back Cangu or Kuta beach....but if they get in trouble - I do feel some responsibility to help out. Given I've been in the water for 40 years.
Some of the posts before me did mention islands etc. But I just don't feel right about that. Hence the discretion - The letters were pretty obvious anyway.

Mike

wallpaper's picture
wallpaper's picture
wallpaper commented Wednesday, 6 Nov 2019 at 9:01pm

nah just kidding mate. I just thought if it's like that it would be a good place to avoid.

and don't please don't respect me because I'm a regular on the chats. Respect me because I'm loaded with money and spoilt to the shithouse with my totally cushy job or none at all when I feel like it and in a position to be able to assist the country and the world in general instead of just being a whingy whiny scabby selfish weak cunt.

again just kidding on all counts.

Jackilegz's picture
Jackilegz's picture
Jackilegz commented Sunday, 3 Nov 2019 at 11:57am

Does anyone know the historical affects of a high IOD index during the Ments off season?

Craig's picture
Craig's picture
Craig commented Sunday, 3 Nov 2019 at 2:41pm

The IOD weakens into the off season so has no effect. But this year because it’s so strong it will continue to influence the region over the coming months. 

tango's picture
tango's picture
tango commented Sunday, 3 Nov 2019 at 3:30pm

Just had a week in nth ments. As you'd expect, temps on land are also cooler both day and night which was about the only upside. Dry as a bone. S and SE the whole time, though patches of lighter winds. Lots of jellies but didn't see any salps float over my board. No storms, no rain the whole time. Water was still boardies, must have been 26 or so but was a noticeable quick chill when you first got wet. There was talk of the 06 event but they reckon nothing like this. The thing that struck me was the lack of current mixing - in my experience in Australia when there is upwelling there's often visible lines on the surface separating warm/cold water, but I didn't see any on our regular forays around the neighbourhood. Possibly due to the consistency of the upwelling and its duration?

wallpaper's picture
wallpaper's picture
wallpaper commented Monday, 4 Nov 2019 at 12:53pm

Around 97-98 was a bad year for southerlies in that region. That was accompanied by serious smoke haze from fires/burnoff happening all over from borneo to the western side of sumatra. In addition to that the water was much cooler than usual and there was a massive algae bloom that resulted in widespread coral bleaching and the death of sealife below water, so things were quite smelly in the surf too and there were other worries with the water quality the way it was. On the flip side, the AUD went up about 10 times against the rupiah over night that year - so swings and roundabouts. (just kidding - it crueled the economy over there, was dry as fuck and the fishing was shot). This year wasn't so bad I thought though bit of a shocker wind-wise.

Spuddups's picture
Spuddups's picture
Spuddups commented Monday, 4 Nov 2019 at 6:17pm

I was there when that financial crisis hit. When I arrived I think it was something like RP2500 per USD. When I left it was something like 25000, so yeah, ten times. I'd fucked my knee so I was moping round Kuta trying to get a flight out. The upside was that I was living like a farken' king due to the exchange rate. Bintangs were working out at something like 20c a pop. When I left I gave the people where I was staying some cash. I think it worked out at a months wages each for them so they were farken' stoked. Crazy times.

Allargo's picture
Allargo's picture
Allargo commented Monday, 4 Nov 2019 at 1:12pm

Great Article- explains a lot of things!

donweather's picture
donweather's picture
donweather commented Monday, 4 Nov 2019 at 2:06pm

Good article Craig. Does the IOD chart above go back any further in time? Late 90’s?

Also any info on what the swell and winds did in Indo in July-Oct 2016?

Craig's picture
Craig's picture
Craig commented Monday, 4 Nov 2019 at 2:16pm

Thanks Don, yeah, see this one...

And looking at winds, looks like there were anomalous NW through that period..

August..

Sept..

donweather's picture
donweather's picture
donweather commented Monday, 4 Nov 2019 at 2:51pm

Beautiful thanks Craig.

Any links to those wind charts please? And the yellow colour represents?

Craig's picture
Craig's picture
Craig commented Monday, 4 Nov 2019 at 3:11pm

Ah yes, when saving the image it doesn't have the scale, just added in.

And here.. https://iridl.ldeo.columbia.edu/maproom/Global/Atm_Circulation/Sea_Level_Pres_Anom.html

freeride76's picture
freeride76's picture
freeride76 commented Monday, 4 Nov 2019 at 3:05pm

greenbush

Craig's picture
Craig's picture
Craig commented Monday, 4 Nov 2019 at 3:07pm

And a few other locales..

Blowin's picture
Blowin's picture
Blowin commented Monday, 4 Nov 2019 at 3:12pm

Don’t be mistaken, there has been plenty of great surf getting around.

Craig's picture
Craig's picture
Craig commented Monday, 4 Nov 2019 at 3:15pm

Yeah for sure, just wind limited at some spots and times of the day.

Blowin's picture
Blowin's picture
Blowin commented Tuesday, 5 Nov 2019 at 6:56pm

Craig : personal prediction time .....you reckon this IOD will still have legs by December ?

No drama,mate . Just an opinion if you have one. Cheers.

Craig's picture
Craig's picture
Craig commented Wednesday, 6 Nov 2019 at 7:15am

Yep, it will have legs. Click through here for the forecast of the strength of the IOD over the coming months..

Indian Ocean Dipole (IOD) outlook

Click the month, ie December and most model forecasts (grey bars) still have the IOD being around 1, weakening below thresholds of a + event into January.

Horas's picture
Horas's picture
Horas commented Wednesday, 6 Nov 2019 at 1:25am

Sai diramoti Tuhani ma hita saluhutna,Tuhan makkaholongi hita ganup marsada -sada .Tuhan mangaramoti saluhut halak Batak naadong diluat portibion. Lissoi ,HORAS ....HORAS........HORAS............! mauliate godang. Indonesia farken pumped thru October cool water or not.

Horas

wallpaper's picture
wallpaper's picture
wallpaper commented Wednesday, 6 Nov 2019 at 9:10pm

surfing tuk tuk were we

Distracted's picture
Distracted's picture
Distracted commented Wednesday, 6 Nov 2019 at 1:16pm

If it is the IOD causing the drought on the NSW east coast, hopefully it packs up soon. If there is no major rain event in the next 8 weeks then will be looking at lowest annual rainfall in 130 years of records on the Mid North Coast.

Craig's picture
Craig's picture
Craig commented Wednesday, 6 Nov 2019 at 1:21pm

IOD currently, but then we've got these negative SAM events over the coming month or two from the Sudden Stratospheric Warming Event.

Shift in westerly storm track further north, and subsequently the sub-tropical ridge north, stopping moist easterly winds to flow into the East Coast. Hence drier and warmer than normal.

Double whammmy.

freeride76's picture
freeride76's picture
freeride76 commented Wednesday, 6 Nov 2019 at 9:15pm

I really think the persistent Tasman sea heatwave is causing weaker and more mobile high pressure in the normal Tasman sea belt, disrupting the tele-connection with Pacific moisture and leading to long term moisture deficits via much weaker Tradewinds flows in Tasman and southern Coral Seas.