Swellnet Analysis
Craig Brokensha

Tropical Cyclone Dylan blowin' in the wind

After one of the slowest starts to the Gold Coast surf season in recent memory, the first tropical cyclone for the year is expected to develop over the coming days in the Coral Sea, near the Solomon Islands. Tropical Cyclone Dylan will certainly provide some long overdue colour to the Queensland WAMs.  

The change in outlook is related to an active monsoon trough across northern Australia, along with the help of a weak Madden Julian Oscillation signal over the Western South Pacific, helping spawn a tropical cyclone in the Coral Sea.

Tropical Cyclone Dylan is forecast to form in the Vanuatu region later this week and slowly drift south into a broad and established easterly trade-flow.The trade-flow itself is expected to produce 3ft+ surf across SE Qld and Northern NSW later this week, but as Dylan drifts south into this active synoptic setup, winds should strengthen and reach the gale to severe-gale-force range on top of an already active sea state.

The one factor working against the formation of a large and prolonged easterly swell event is the fact that as Dylan drifts south, the supporting ridge to its south will weaken resulting in a split fetch of E/NE winds feeding into the cyclone on its eastern flank and SE winds on its western flank.

Ideally we want an uninterrupted fetch of E'ly winds spread out nicely below the tropical system.

In saying this a strong pulse of groundswell is still expected across SE Qld and Northern NSW, peaking on Monday in the 4-5ft+ range. The rapid southward movement of TC Dylan towards New Zealand during Sunday and Monday though, will result in a short-lived one-day swell event that will back off rapidly into Tuesday and further Wednesday.

Unfortunately from Seal Rocks south, not much size is expected, with Sydney beaches only likely to see very inconsistent 2-3ft sets on Tuesday.

While the first cyclone swell of the season is expected to be quite short-lived, Dylan may pave the path for a secondary stronger tropical system less than a week later. We'll keep a close eye on this and provide running updates in the commentary below.

There is a chance this cyclone may be named June by the Fiji Meteorological Service if it forms east of 160E, but it's too hard to call at this stage.

Comments

fitzroy-21's picture
fitzroy-21 commented Wednesday, 15 Jan 2014 at 11:59am

Pretty ambitious calling it a cyclone. Tropical low, yes, but unless it suddenly bombs below 986....................

Most welcome pressure gradient though for us surf-starved up here.

fitzroy-21's picture
fitzroy-21 commented Wednesday, 15 Jan 2014 at 12:09pm

Sorry, not having a dig, just a general comment.

Everyone seems to get so excited these days when a low will get around the 986 mark they just go "lets call it a cyclone" . (BOM and mainstream media beatup).

As long as I get swell at the moment I might not be so grumpy and picky.

thermalben's picture
thermalben commented Wednesday, 15 Jan 2014 at 12:15pm

There's no MSLP threshold requirements for the naming of a TC.

We've discussed in the past how overrated tropical cyclones generally are as 'epic surf producing weather systems'. However, this one looks pretty good right now.

Craig's picture
Craig commented Wednesday, 15 Jan 2014 at 12:16pm

No need for the apology, I'd be all antsy and on edge as well if I had the summer you guys have had.

And there is no threshold in pressure in which a system has to dip below before it's named a cyclone.

All it needs to be classified as a Category 1 system is average sustained winds of 35kt or above over a 10 minute period.

Craig's picture
Craig commented Wednesday, 15 Jan 2014 at 12:17pm

Ah, Ben slightly beat me to the punch there.

fitzroy-21's picture
fitzroy-21 commented Wednesday, 15 Jan 2014 at 12:29pm

I didn't know that one guys. Thanks for the heads up. I've come from the old learnings from crusty old skippers that I worked for as a grom and they taught me the threshold was 986. Whilst 35kts at sea isn't the most comfortable conditions to be in, its not scary,bad, get the hell out of here, like a "cyclone". Splitting hairs I guess.

Geez I need a surf. Haha. I am seriously looking forward to some uncrowded waves with some size (above knee height) and grunt though.

mitchvg's picture
mitchvg commented Wednesday, 15 Jan 2014 at 12:37pm

what about SSTs above 26.5(?) and continuous rotating winds?

Craig's picture
Craig commented Wednesday, 15 Jan 2014 at 12:43pm

Yep, SST's around where the tropical depression is expected to deepen are around 28-30 degrees and it's also in a low sheared environment (weak upper level winds). At the moment there is only weak circulation and poor organisation.

mitchvg's picture
mitchvg commented Wednesday, 15 Jan 2014 at 12:58pm

So are those requirements for a TC? As designated by the JTWC(?)

Craig's picture
Craig commented Wednesday, 15 Jan 2014 at 1:12pm

There's actually different scales and criteria world wide on the naming and classification of cyclones.

Australia and Fiji follow the same criteria, and this is slightly different from the JTWC.

Australia use 10 minute averaging of maximum sustained wind speed, while JTWC use 1 minute averaging. China use a different method again, being 2 minute averaging.

mitchvg's picture
mitchvg commented Wednesday, 15 Jan 2014 at 1:27pm

haha ok I see why you kept the main article brief

Craig's picture
Craig commented Wednesday, 15 Jan 2014 at 12:47pm

One thing to also note is that it could be actually be named June by the Fiji Meteorological Service if it forms east of 160E.

mitchvg's picture
mitchvg commented Wednesday, 15 Jan 2014 at 12:59pm

So is that a boy's name? Ponting keeps calling Mark Waugh "June" on the T20 cricket and I have no idea why!

Craig's picture
Craig commented Wednesday, 15 Jan 2014 at 1:13pm

June in this instance is a female name :)

fatjackdave's picture
fatjackdave commented Wednesday, 15 Jan 2014 at 1:53pm

Mark Waugh is "junior" - the younger of the two Waugh twins

mitchvg's picture
mitchvg commented Wednesday, 15 Jan 2014 at 10:47pm

Ahhh yeah I've heard that at times too. Don't mind them now they're allowing their personalities to come out more

messmate's picture
messmate commented Friday, 17 Jan 2014 at 3:41pm

I think that may be short for "junior" as in younger brother of Steve?

shoredump's picture
shoredump commented Wednesday, 15 Jan 2014 at 1:08pm

Oh great, a trans gender cyclone.

Whoever "it" is, it's great timing for the save Kirra paddle out.

donweather's picture
donweather commented Wednesday, 15 Jan 2014 at 1:50pm

Geez, New Cal couldn't be in a worse spot with respect to fetch dissection in the early phases of Dylan!!! And that's the best swell window for us SE Qlders!!!! Grrrrrr!!!! Also, Craig, why do the models show such better swell on the SW/W flank of Dylan as it's tracks S/SE compared with on the S flank? It doesn't quite make sense to me as the fetch on the SW/W flank is moving away from the swell producing winds. Is it just the length of the fetch is longer on the SW/W flank compared with the southern flank? Models are also indicating the winds to be stronger on the SW/W flank compared with the southern flank? Again I don't understand this as the nearest area of high pressure is NE of NZ, hence the greater pressure differential should be more so on the southern flank (and even more so on the SE/E flank which is it) than the SW/W flank?

Craig's picture
Craig commented Wednesday, 15 Jan 2014 at 2:11pm

I'm not totally across why, even though the high pressure ridge is sitting south-east of the cyclone, and pressure gradients seem strongest there, that the actual strongest winds are being produced on the SW flank of the system.

I'm guessing this is due to the complex vertical structure of cyclones through the atmosphere.

And our model guidance is varying between model runs by about 2 - 2.2m @ 10.7 - 11.2s at the swells peak. This morning the Gold Coast forecast was 4-6ft on Monday, but it's gone back to a flat 5ft in the most recent model update.

donweather's picture
donweather commented Wednesday, 15 Jan 2014 at 1:52pm

Based on the above, I'm wondering if the models might be undercooking this one (swell models). What's your in house swell model calling for the peak of the swell for SE Qld (swell height and period)?

mitchvg's picture
mitchvg commented Wednesday, 15 Jan 2014 at 2:21pm

NY day swell last year was over cooked; it generally had a similar setup, being partially tucked behind New Cal. So maybe a medium rare swell isn't so bad of a call...

freeride76's picture
freeride76 commented Wednesday, 15 Jan 2014 at 2:55pm

DonW, it's because pools of warm water have been coagulating in a series of NW/SE aligned eddies from the SPCZ down to the area SE of NZ. Look at the SST anomaly charts.

That is making the highs weak -hence no trade swells this summer-and not allowing sufficient pressure gradient differential with the cyclone to strengthen fetch on southern flank.
The cyclone, thus, is acting more like a cut-off system and these typically have strongest winds on W or SW flank.

I dunno about this system. Moving obliquely to the circle paths and pretty compact. Duration limited fetch. I'm keeping expectations modest.
Still, on the very positive side, it won't be a bank buster and that is a blessing.

donweather's picture
donweather commented Wednesday, 15 Jan 2014 at 3:13pm

Cheers Steve for the detailed and very informative response.

mitchvg's picture
mitchvg commented Wednesday, 15 Jan 2014 at 3:23pm

If you look at the 100-500hPa thickness, cool air is being forced between it and us. The mid level winds to the east are strong. Gradient level winds are stronger on S/SW flank... (all on Sunday). Looking at the WAMS, there is the slightest of troughs between Cook Straight and the Mid North Coast, with pre-frontal NWs.

So I guess that on Sun/Mon:
- there is a cooler air mass from the Southern Ocean; moderately cooler air from the departing (over NZ) high; the low/TC.
- So along the boundary of the sthn airmass/trough, is where the greatest friction is. And therefore greater pressure (not simply central pressure) difference is, and corresponding winds...
- The mid level winds prevent the low from moving east.

freeride76's picture
freeride76 commented Wednesday, 15 Jan 2014 at 6:16pm

Latest GFS shows potential for an extra-tropical transition down the inside corridor aka the Tasman sea.

That could be a game changer.

donweather's picture
donweather commented Wednesday, 15 Jan 2014 at 7:42pm

Latest EC for Sunday looks damn good!!!!

southey's picture
southey commented Thursday, 16 Jan 2014 at 4:55am

i was going to suggest that its expected to transition Early . ( which will help you guys in the surf stakes ) .

Steve , that Thermal mixing is most likely due to the current " La Nada " conditions in the Pacific .

The bigger they are , the harder they fall .

freeride76's picture
freeride76 commented Thursday, 16 Jan 2014 at 8:11am

Deffo Southey.

Latest runs are looking tastier with a slowing and slight drift back into the Tasman. If there is an ETT during that stage it could be on like donkey kong.

bondihq's picture
bondihq commented Thursday, 16 Jan 2014 at 8:19am

all you weather forecasting gurus make me feel like a dunce ha ha.....i will be at port macquarie from friday until wednesday - what can i be expecting on my little break to the lovely port maq for the duration - looks like i may have picked a good time to get up there....maybe

thermalben's picture
thermalben commented Thursday, 16 Jan 2014 at 8:25am

Yeah looking pretty good for Monday BHQ. 3-5ft out of the E/NE with a moderate S'ly wind. I can think of a bunch of points and reefs that will enjoy that combo!

https://www.swellnet.com/reports/australia/new-south-wales/port-macquari...

bondihq's picture
bondihq commented Thursday, 16 Jan 2014 at 8:31am

thanks TB - looks like ive timed it well......cheers

shoredump's picture
shoredump commented Thursday, 16 Jan 2014 at 11:15am

Keep those updates coming boys, I'm heading up there sat - mon for the BDO. Now I've got a cyclone & the morning off re no Kirra paddle out. Already suggested to my accommodating wife that Monday will be worth hanging around for. Yew.

Craig's picture
Craig commented Thursday, 16 Jan 2014 at 11:20am

Latest updates have it coming in strongly Sunday afternoon and holding Monday. Biggest waves look to be found through later Sunday and Monday before dropping off steadily into the middle of the week.

Secondary system looks to generate plenty of swell a week later as well!

drewdrewdrew's picture
drewdrewdrew commented Thursday, 16 Jan 2014 at 9:07pm

Craig does this mean we may see something in the northern beaches Sunday afternoon? Or only further up the coast? Thanks

Craig's picture
Craig commented Thursday, 16 Jan 2014 at 9:34pm

Drew, this swell won't start filtering down into the Northern Beaches until Monday and is expected to peak Tuesday.

Craig's picture
Craig commented Friday, 17 Jan 2014 at 10:58am

Tropical Depression 08F, the system that's expected to form into a tropical cyclone has just crossed the 160E boundary between Australian and Fiji met agencies and now FijiMet get the naming rights.

So Dylan has put on a frock and dolled up to now be named June later this afternoon/evening.

shoredump's picture
shoredump commented Friday, 17 Jan 2014 at 12:04pm

Winter, you could say, is coming early!
Those wams for next week look impressive. Gonna be a sustained run of swell for the cane toads.

donweather's picture
donweather commented Friday, 17 Jan 2014 at 12:21pm

SD, I'd be taking the long range GFS model (WAMs) with a grain of salt. GFS is certainly the outlier with respect to it's long range prognosis for further intense cyclogenisis.

thermalben's picture
thermalben commented Friday, 17 Jan 2014 at 1:42pm

The current Fiji Met forecast track has it moving right over the top of Norfolk Island (albeit as a tropical low).

Craig's picture
Craig commented Friday, 17 Jan 2014 at 3:51pm

She's starting to consolidate:

Craig's picture
Craig commented Friday, 17 Jan 2014 at 5:44pm

Tropical Cyclone June has just been named and is currently a Cat 1 system.

http://www.met.gov.fj/aifs_prods/65648.html

many-rivers's picture
many-rivers commented Friday, 17 Jan 2014 at 5:58pm

The Elders weather website also has a prediction of substantial ( thank you ! ) rain from Tuesday to Friday accompanied by north easterly winds around the mid north coast.
They are only predicting easterlies on Sunday am turning to east south easterlies for Sunday pm to Monday pm only.
Is the rain the after effect as June turns into an east coast low or is another system coming through causing the rain?The BOM 4 day maps show several lows forming.....

mitchvg's picture
mitchvg commented Friday, 17 Jan 2014 at 7:27pm

mANY rIVERS I'd say that it's related to the inland trough on NSW, moist E'lies feeding into it.

Click on your preferred region here http://www.bom.gov.au/nsw/forecasts/map.shtml and there will be a brief "weather situation" note above the forecast conditions.

udo's picture
udo commented Saturday, 18 Jan 2014 at 3:59pm

craig, freeride , donweather is Dylan /june moving away from aust coast faster than first thought ......craig any changes to fridays east coast forecast notes ?

Craig's picture
Craig commented Saturday, 18 Jan 2014 at 5:58pm

Nah, tracking as per the models have been forecast. Probably looking at a peak around 5ft at exposed spots on the Gold Coast and Northern NSW coast.

matt123's picture
matt123 commented Saturday, 18 Jan 2014 at 4:15pm

Hopefully the winds stay away tmorrow and monday few good banks around the Goldy. Looking pretty light at this stage ?

Craig's picture
Craig commented Saturday, 18 Jan 2014 at 5:59pm

Yeah winds great Monday morning.

shoredump's picture
shoredump commented Monday, 20 Jan 2014 at 4:45am

Last nights Big Day Out, Pearl Jams Eddie Vedder drags on stage Mick & Occy for the encore Rockin In The Free world, where they all sing & jam out the finalé. Ok our boys had tambourines, but everyone on stage looked stoked at what was going down. Eddie seemed pretty chuffed he finally got to meet Occy, Mick seemed more embarrassed than anything, & Occy, well he was just getting started!

thermalben's picture
thermalben commented Monday, 20 Jan 2014 at 8:05am

Latest OSCAT returns looking a little more promising for the southern half of New South Wales. Will have to delve a little deeper into the data but there's a healthy region of 50kt E/NE winds here which should kick up more size than the projected 2-3ft peak for tomorrow, probably arriving a little later too- ie late Tues/early Wed.

(note: we've actually had some model issues over the weekend, and it appears we're lagging a day or so behind with updates.. so perhaps the models have resolved this upwards since then)

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