I thought I had my head around what storm surge is, a combination of local low pressure allowing a higher pressure somewhere else to move water in and strong onshore winds pushing water in.
Well the last couple of days here, we've been in the middle of a high pressure system and had off shore winds, today we had almost 20cm of positive storm surge.
How can this be???

Tide came in ?

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Carantoc said..
Tide came in ?

Yes well as you can see from my edit above, the tide did come in, but so did the storm surge.
This is the sort of surge we get with a strong winter storm with low pressure and strong on shore winds.
To day was the exact opposite, nice and sunny with moderate off shore winds and high pressure.

I thought the difference between actual and predicted tide isn't necessarily only a storm surge.

Tides are caused by a number of factors not only the gravitational influence from the moon and sun.

These include shoaling, funnelling, reflection, resonance, sloshing, (the one where the rotation of the earth causes bigger tides on one shore of a channel then the other, forgotten the name), seasonal mean sea level changes, storm surge (made up of both atmospheric pressure and surface wind effect), ocean currents and several other things.

The prediction of tides is based the known fairly predicable motion of the moon and sun corrected by past measurements compared to past predictions for the local effects. It isn't an exact science. Although generally for a straight, open coastline like WA the local effects are pretty small, hence the small tides in most of WA. So a 20cm difference with no apparent reason for a storm surge does seem interesting.

Your edit shows for Mandurah marina. Are all the other Perth observations the same, or was it just a local marina observation difference ?

Thanks Carantoc, that's a good question, so here's Freo's




Looks very similar, so it's not just local.
I'll go and look at a few more, further afield and see just how far the effect is.
Be back in a jiff.
OK it didn't get to Albany, that's neutral
But Busselton is a tad more almost 25cm
Geraldton is also just over 20cm
Carnarvan also around 20cm
Exmouth is less closer to 10cm
And Wyndham is negative 0 to -30 through the day, but their tides are huge from 3m to 6m

So that's quite a large strip of the western coastline affected by whatever it is.

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decrepit said..
I thought I had my head around what storm surge is, a combination of local low pressure allowing a higher pressure somewhere else to move water in and strong onshore winds pushing water in.
Well the last couple of days here, we've been in the middle of a high pressure system and had off shore winds, today we had almost 20cm of positive storm surge.
How can this be???

Me and 'Ken got in the water at the same time?

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fangman said..

decrepit said..
I thought I had my head around what storm surge is, a combination of local low pressure allowing a higher pressure somewhere else to move water in and strong onshore winds pushing water in.
Well the last couple of days here, we've been in the middle of a high pressure system and had off shore winds, today we had almost 20cm of positive storm surge.
How can this be???

Me and 'Ken got in the water at the same time?

If it was only the estuary involved I could believe that.

Wonder if that low of the coast could have had anything to do with it. But it does seem strange with the low do far offshore and no onshore winds.
Maybe the real position of the low was closer to the coast than the map shows.
I suspect something else is at play though and that someone will know the answer.

Mmmm, every station Carnarvon to Busselton would seem to imply it is not just an isolated reading or a blip in the prediction. Seems a fairly consistent rise as well, 3 days of increasing surge.

Maybe an eddie in the Leuwin current off Perth, or the current running closer to shore or something ?

Good question Decrepit.

I was wondering the same thing while out boating on the swan river with the kids yesterday.

The tide was very high even though it was another day with a strong morning offshore wind.

A cold front is expected to hit the SW early on Wednesday. Could this be the cause?

Is it even possible for a cold front thousands of km's away from the coastline create a storm surge on that coastline?

Hopefully someone can explain....

The Nautilus is visiting, you're seeing its hull displacement

Hmmm well the centre of that low is closer to Albany, and that's not affected, an anomaly in the leuwin current sounds more plausible

They added all the fluoride to the wrong water today.
New guy - sacked.

Displacement from the USS Carl Vinson?

I did land a very high backloop a bit flat.....

Hmmmm,.. Very interesting,.. and it's just as I thought. I have no idea what's causing it.

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decrepit said..
I thought I had my head around what storm surge is, a combination of local low pressure allowing a higher pressure somewhere else to move water in and strong onshore winds pushing water in.
Well the last couple of days here, we've been in the middle of a high pressure system and had off shore winds, today we had almost 20cm of positive storm surge.
How can this be???

I'd be more worried about those weird broken isobars myself! Is there an explanation to this? What happens at the boundary? Do you get really strong tip vortices where the pressure gradient has a complete discontinuity? How does Coriolis affect this?

Man, we're going to hell in a handbasket.

Wow Nebs, I didn't even notice them, have they just appeared?
Does anybody remember this map when they were joined up?
Have I just skipped alternative universes, or is there another explanation?

Well there ya go..... Looks like it's the same sort of area we lost a plane not long ago, tip vortices you say?

Never heard of them

I'd say more than likely someone didn't connect the dots up right out of spite for having to work the long weekend (over this side anyways) That'll teach them, he says

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WazzaYotty said..

Not so much the fat guy but... Earthquake in Nepal?
Granted its a long way from the coast but... maybe the whole plate moved ??



not had a coffee yet so brain not functioning...

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decrepit said..
Wow Nebs, I didn't even notice them, have they just appeared?
Does anybody remember this map when they were joined up?
Have I just skipped alternative universes, or is there another explanation?

It's clear evidence of a rent in the space-time continuum. We're doomed! We're all doomed!

www.solarsystemscope.com/models

hi decrepit
since you are looking at these things, you will probably recognise that though slightly unusual to be sustained like this in the current climate, 10-20cm is not that great as a residual on top of the anticipated tide - storm surges are typically 40-50cm in the local waters you are looking at once you get wind and wave set up on top of barometric pressure, and i guess they are just a bit shorter duration than the one noted here.
i like the state wide comparison as well so that you can see if it is something "moving" along the coast as the pressure system approaches, or something more localised.
www.transport.wa.gov.au/imarine/storm-surge-comparison-chart.asp

i expect it is just transfer of water level from the high pressure area to the low pressure area, then being 'bent' onto the coast by the coriolis force (left in southern hemi - so lines up if you want to visualise). but don't take my word for it, i'll ask some more knowledgable persons then myself for you and see if they'll post.

a note on the other local effects mentioned, there are seiching and shoaling effects based on local bathymetry and wind conditions that will increase or decrease levels at the tide gauge, but you aren't really seeing the full picture on the DoT plots online. you have to zoom into the scale of seconds or minutes etc to do that.
you can see the shelf or basin scale oscillations on some of the plots though, which are those quite regular periodicity peaks and troughs inside the tidal pattern at somewhere like carnarvon or busselton
www.transport.wa.gov.au/imarine/carnarvon-storm-surge.asp

the other one that is pretty interesting is when a pressure system passes the coast really quickly, and it sets up a wave like a tsunami of sorts that then travels along the coast - and you can see it "hitting" each tide gauge or facility. the UWA guys are right onto watching and tracking these nows. it was one of these that dislodged the ship that hit the freo traffic bridge a while back too.
if you have time, try to attend this if you are interested:
www.engineersaustralia.org.au/portal/event/meteotsunamis-south-western-australia

i should get back to working now - cheers
maz

thanks for the info Maz - interesting stuff!

It's chemtrails. They're dissolving your isobars. They are breaking up and the pressure is escaping so the water is rebounding.

Yes thanks Mazdon, just goes to show that things can be much more complicated than you think they are.

Seismic activity is my bet. Measurable variations to the predicted tides were observed at ports all around Australia following the Asian tsunami.

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mick14 said..
Seismic activity is my bet. Measurable variations to the predicted tides were observed at ports all around Australia following the Asian tsunami.

I think it's lasted too long for that.

I'd go straight to this page for an answer
www.bom.gov.au/oceanography/forecasts/idyoc10.shtml?region=10&forecast=3
I don't know the area well, but probably a strong warm pulse from the leeuwin current or a strong ocean eddy. Looks like there is a decent coastaly trapped wave going down the coast and off to SA.