Rare Fujiwhara Effect occurring off WA
A rare weather phenomenon is developing off the West Australian coast as two brewing cyclones look set to interact this week.
Tropical Cyclone Seroja, currently sitting several hundred kilometres north-west of Broome, was named earlier this week and is tracking south-west over open waters.
Meanwhile, a second tropical low has now formed nearby, expected to strengthen to cyclone intensity as early as Thursday.
With the two systems on path to interact with each other, a phenomenon known as the Fujiwhara Effect will likely occur, causing them to rotate around each other.
TC Seroja and TC 27S spinning clockwise around each other, know as the Fujiwhara Effect
Bureau of Meteorology (BOM) tropical cyclone forecaster Craig Earl-Spurr described the complex interaction as similar to a "dance" between the two systems, rarely seen in Australia.
"Because both are trying to throw each other around their own wind fields, as each one moves the wind field moves with it," he said.
"So depending on how that then pushes the other [system] around, little changes can become big changes very quickly."
What will the impacts be for WA?
Holiday-makers and residents on the west coast are being urged to stay alert and prepare for severe weather from Saturday to Monday, anywhere between Onslow and Perth.
The BOM's forecast map from Wednesday afternoon predicts TC Seroja will hit the WA coast as a fast-paced Category One on Sunday or Monday anywhere between Coral Bay and Perth, but most likely between Carnarvon and Jurien Bay.
Meanwhile the tropical low could hit the west Pilbara coast on Saturday, but may take a sharper turn and avoid the coast altogether.
The speed of TC Seroja when it hits the WA coast is expected to be travelling at least twice as fast as a normal cyclone would, at 35–40km an hour, which could bring intensive rainfall over a short period, high winds and high seas off the coast.
Mr Earl-Spurr said the "tug of war" between the two systems made predicting cyclone tracks difficult, and it could change very quickly.
"They can take a full 90-degree turn when they first start to interact with each other," he said.
Will they merge to form a mega-cyclone?
The good news is their interaction means it is more likely their track will be impacted rather than their intensity.
"It's unlikely that one of them would become significantly stronger through the interaction," Mr Earl-Spurr said.
"They could intensify afterwards, once they're kind of no longer interacting with each other."
There is also a third tropical low currently to the far west over the Indian Ocean, but Mr Earl-Spurr said this was unlikely to add to the interaction at this stage.
The weather phenomenon was named after Japanese meteorologist Sakuhei Fujiwhara, who originally described it in 1921.
© Australian Broadcasting Corporation. All rights reserved.
Comments
And what about the swell potential ;)?
Keep an eye on the WA notes, I went into detail Wednesday but will have an update tomorrow.
Quite late in the season for TC's off WA yeah? I assume the MJO is currently in the Indian Ocean and due over in the western pacific in a week or two?
Yeah MJO across our north bringing all the current tropical activity..
Like two black holes dancing around one another. I think they found evidence of such an event in recent astronomical news.
I'd never name a child 27S.
Haha, wonder why no name eh?
Crazy hey, blackholes, cyclones, even the sand patterns in the shallows at the beach break-same configurations on massively different scales.
Hmm seems a bit quick but a couple rare fickled possible waves may light up...
Do these cyclones have anything to do with the bombing low below them as the winds all seem connected when you look on a larger scale and a couple of years ago in early feb we had a bombing low which interacted with the remnants of a cyclone or am i tripping
Nah not this time, but the remnants of a cyclone absorbed into the westerly storm track can cause a rapid intensification and low to bomb.
Hitting Kalbarri on sunday with a blue elert issued already...All caravans and campers are leaving town.
120km hour winds expected...power will probably blackout and for at least 12 hours with my last grocery shopping filling up all my freezers...will probably go off.
Long as we don't get Fukushima'd by the fujiwhara thingy. batten down,
You can always count on good ol mother nature to shorten things up when we mere mortals start to think we are the dominating force about the place.
Sad, but true.
Interesting, but a shame we won’t get a north cyclone swell from it like a few years back.. was so epic at the local beachy that doesn’t usually pick up swell...
Going to be a good daisy season after that low heads inland.
Mind blowing that theres nearly a secondary Fujiwhara Effect as the SAME system moves into the great Australian bight on mon/tues. Check out ex Seroja and that southern low as ex seroja moves back over water off Esperance. Everyone in South Oz, Vic, and tas should be dusting off the guns. The ghosts of Bells 81 maybe?
http://www.metvuw.com/forecast/forecast.php?type=rain®ion=swp&noofdays=8
Yep been keeping a close eye on. Models didn't like at first but now going for a strong low.
Deja Fu
We will have just cleaned up the beach after tomorrow's event. (Which is getting bigger in the telling along the grapevine round here)
Some solid sets at Ulu atm - cyclone produced Craig ?
https://balibelly.com/pages/uluwatu
You're always onto it Udo.
1-2 ft waves being surfed at cable beach Broome today
Ex Odette is wet creeks flowing on the cape. Surf is a mess. Yes indeed distracted, endless color daisy season.
Was staying at Pops shack at lucky bay, just south of Kalbarri. Basically exactly where it’s likely to cross. Headed back home today. Heaps of crew heading back south but also lots heading north for holidays in Exmouth etc. Got to beat the road closures.
You've got no idea how many times i've busted out Fujiwhara effect in casual convos lately. Cheers for the new word!
Interesting note, in the last decade or so, a couple of the last major whale strandings have taken place in SW WA after North swell from cyclones. Related or unrelated, too hard to pinpoint but could be worth noting, and hoping the whales have worked it out on past referencing and keep a wide berth during this one.
Hi BD, When I was studying marine biology in NZ I attended a conference on whale standings. There was a theory around that standings and bombing lows might be linked. One of the met guys suggested it would be a good research topic with all the data in the record. I always kind of regret I didn't take it on.
There was some suggestion it may impact their sonar in shallow water. This related to pilot whales and one of the main motivations to resolve standings was just how bloody expensive they are to clean up. Whale suffering also rated highly of course. If they could establish when standings may happen then they could gear up to redirect the whales.
Wow, that's pretty interesting Yendor. Yep, can imagine a solution to cleaning up would be a priority, hence the research.
Super interesting that theory about bombing lows.
I just had a look back at that mass stranding off the W Coast of Tassie last year, and this is the weather event that correllated roughly to the time frame of the stranding..(can't be certain of exact date of strandings due to remote coast).
http://www.bom.gov.au/cgi-bin/charts/charts.browse.pl
You can see that low coming in from the West straight at the Tassie coast and it's pressure drops pretty severely.
That would support your theory?
Here's a link to the stranding, which i'm sure you're probably all over anyway.
https://www.livescience.com/tasmania-mass-whale-stranding.html
Cheers for that feedback. Super interesting.
Ahh that link for the synoptics didn't work but i just looked at the week from Sept 17 through to September 22 2020....
im calling this cyclone a fizzer a few forecast sites have it die out west of exmouth with only 45km winds max...the two have joined but not coming south.
yeah just had a look at the maps properly. Agreed. It's a dud. Lots of wind and rain heading through the interior though! Maybe Lake Grace will fire up! Maybe even a little kick in the tail as it heads out to the Southern Ocean.
Was never gonna be a good surf producer but winds are way stronger than 45km/h
heres one, i find this site fairly accurate for north west coast and indo too
https://www.surf-forecast.com/breaks/Jakes/forecasts/latest
nah that site was wrong sorry Craig earth nullschool has it on track to the other forecast you showed.93km winds atthe moment in the cyclone.
Good Cyclone History site
https://australiasevereweather.com/tropical_cyclones/bom_1975_1976_austr...
Sun city could become flood city by the looks. I hope and pray for an okay outcome. Recent footage of Greenough rivermouth showed absolute filthy mud waves quite nice shape too.
Would be good to see some footage or after pics. Especially of the coast between Kalbarri and Gregory. Dunes are going to cop a hammering.
One of my mates here lives in a home made shack...could be in trouble.
You guys stay safe up there GS
Shacks at lucky bay could be in trouble. Happy we convinced the old fella to stay at a mates place in Gerro.
Been raining all day down here, 30mm in my gauge
Still reas quite ATM for Exmouth
https://wind.willyweather.com.au/wa/gascoyne/exmouth.html
Still Cat 3, oh boy. Buildings down that low aren’t built for this shit.
Boom - 100 k gusts
https://wind.willyweather.com.au/wa/midwest/geraldton.html
Quite a bit of the foreshore at the CBD is pretty low lying...
Bit off topic (well majorly) but does Craig or anyone have a link for a longwave trough plot? Weatherzone.au seems to regularly drop the link and their site is a nightmare to navigate.
The filtered 500hPa variable from GFS has been removed from the latest model update, hence WZ not having the charts any more, same with us.
We'll have to reproduce them just using the 500hPa geopotential height, but in the meantime on weather forecast sites look at the 500hpa height to get a good idea.
Thanks Craig that works.
Not good news coming from the mouth of the Murchison this morning, lots of damage done.
Hows how it dies off in intensity then hits shark bay and doubles in intensity as it hits Kalbarri.
My place is fucked roof badly damaged by someone else's 40ft by 40ft roof with solar panels all over it.
smashed into my lounge room and roof breaking about a hundred tiles and all the windows..glad this place wasn't fibro cause i and my brother would be dead.
about 40% of houses no roof..army came and helped a lot but were sent home due to the amount of asbestos around.Power should be off for 3-4 weeks but i have a genset which im running right now on my pc.
Mates at Northampton are describing the usual bit of post catastrophe thievery going down. Watch your stuff, mate. Some people seem to think that when others get vulnerable that it’s open season on acting like a cnt.