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#1490747 - 17/02/2019 20:24 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Nature's Fury]
james1977 Offline
Weatherzone Addict

Registered: 16/11/2009
Posts: 2946
Loc: collingwood park
Originally Posted By: Nature's Fury
While I really have my doubts that we'll see this system come anywhere near SEQ, EC is doing its best to keep hope alive. In fact the scenario suggested by this evening's run is almost a worst-case scenario for SEQ. The shortwave trough is weaker than expected so the cyclone rides the ridge into WBB, but gets stuck over SEQ as its exit is blocked. The cyclone strikes WBB so all the rain is focused directly south over us. It then wobbles around SEQ for almost four days before exiting through Moreton Bay. This scenario would definitely cause at least moderate river flooding up and down SEQ. Weakening and slow-moving ex-TCs generally cause far more problems for SEQ than a quick severe impact.



Unlikely to happen though.




Such pretty colours
_________________________
I hate winter

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#1490749 - 17/02/2019 20:28 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Nature's Fury]
Mega Offline
Meteorological Motor Mouth

Registered: 03/02/2003
Posts: 7899
Loc: Maryborough, Wide Bay, QLD
Originally Posted By: Nature's Fury
Ken what is the difference between deterministic and ensemble?


Ken could answer this better than me but I believe the ensemble is just the average taken from all of its ensemble members put together. Deterministic is the main run.

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#1490751 - 17/02/2019 20:30 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Blowin' Offline
Weatherzone Addict

Registered: 23/08/2014
Posts: 1009
Loc: Diamond Valley, Sunshine Coast
Wow, interesting few days to see if EC is leading the way or just keeping the forum busy.
Waiting for a Higgins led bread and milk frenzy

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#1490754 - 17/02/2019 20:50 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Ken Kato Offline
Meteorological Motor Mouth

Registered: 05/03/2012
Posts: 6090
Originally Posted By: Nature's Fury
Ken what is the difference between deterministic and ensemble?



In the context of a single model ensemble like the EC ensemble, it's when a single model like the EC (or any other model) is run multiple times to generate a range of scenarios (members).
The EC ensemble always generates 50 members. Each member starts off with slightly different initial states of the atmosphere and oceans. This is because we don't have obs data for every square inch of the whole planet (satellite data covers most of the planet but it has its own degree of uncertainties) - it's these uncertainties in the exact initial state of the atmosphere and oceans that grow and grow as you look further into the future and are one of the biggest contributions to increasing forecast error over time (chaos theory, butterfly effect, etc). So the model uses a sophisticated system to deliberately inject variations (weighted towards the uncertainties which are most likely to cause the maximum forecast errors) into the starting state of the atmosphere/ocean for each member.
If most ensemble members are tightly clustering around a particular scenario (e.g. max temp of 35C for a particular day, 25-50mm of rain, etc), it generally means that the weather setup concerned is insensitive to influences that can throw that forecast off which implies there's a high confidence in that model for that scenario. But if there's a big spread in the ensemble's members, it implies the setup's sensitive to even small changes and uncertainty is high.

In contrast, the deterministic version of a model (the forecasts from models like EC, GFS, ACCESS-G, etc whose forecasts you see on most websites) is just a single scenario.

Most deterministic models have an ensemble version.

The advantage of ensembles is that they give a great idea of how confident or uncertain a model is for particular scenarios. Comparing an ensemble to a deterministic version of a model is a bit like asking a big bunch of doctors for a diagnosis on a hard-to-diagnose disease compared to asking just a single doctor.
One disadvantage of ensembles is that they have lower resolution than their deterministic versions (due to the computational resources they take up) so they can sometimes miss smaller scale details, underestimate the intensity of a smaller than normal intense TC, etc.

There's also multimodel ensembles and grand ensembles... the former are ensembles consisting of multiple deterministic models (WATL and OCF are examples) and the latter are ensembles of ensembles.

So in a nutshell, think of ensembles by their common definition such as that used for furniture i.e. a group of things that are treated as a whole thing. Ensemble = multiple scenarios from a model or models. Deterministic = single scenario from a model.

One thing to note is that a lot of forecast products from ensembles show the average of all the scenarios (e.g. WATL, OCF rainfall amounts, etc). While this is useful, it doesn't show anything about how the scenarios are distributed, if they're skewed, what outliers there are, etc. Therefore I prefer to look at probability forecasts from ensembles (percentage of an ensemble's members going for a particular scenario) and preferably multimodel ensembles because a single model ensemble often tends to be more representative of its deterministic version rather than giving an appreciation of the true range of possible scenarios.

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#1490755 - 17/02/2019 20:55 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Ken Kato]
Nature's Fury Offline
Weatherzone Addict

Registered: 29/11/2009
Posts: 2545
Loc: Brisbane Western Suburbs
Thanks for that Ken, exactly what I was looking for.

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#1490756 - 17/02/2019 20:55 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Blowin']
james1977 Offline
Weatherzone Addict

Registered: 16/11/2009
Posts: 2946
Loc: collingwood park
Originally Posted By: Blowin'
Wow, interesting few days to see if EC is leading the way or just keeping the forum busy.
Waiting for a Higgins led bread and milk frenzy


Itís already started, charging ppl $38 subscriptions to his person track map. Puts up a picture to get interest then says you wanna know more subscribe 😂
_________________________
I hate winter

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#1490757 - 17/02/2019 21:09 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
DDstorm Offline
Weather Freak

Registered: 13/05/2010
Posts: 388
Loc: Tallai, QLD
Great explanation Ken, thx
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#1490761 - 17/02/2019 21:22 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Delta-T Offline
Weather Freak

Registered: 21/01/2011
Posts: 203
Loc: Peachester
That's why we love our Kenny.

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#1490762 - 17/02/2019 21:32 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Ken Kato]
Flowin Offline
Weather Freak

Registered: 15/10/2017
Posts: 966
Loc: Pinjarra Hills, Qld
Originally Posted By: Ken Kato

Most deterministic models have an ensemble version.


I like the explanation of ensembles you gave Ken.
I would like to see a version of ACCESS R or ACCESS C in ensemble form and publicly available. Ensembles also give a better idea of the potential spatial displacement error of heavy rain. It appears to me that the models are getting quite good at big rain events for a region, but the location of heaviest rain can be hard to predict. It is all too easy to get excited about heavy rain bullseye from a deterministic model, but the ensemble helps to better understand potential scenarios.

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#1490763 - 17/02/2019 21:40 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Un_stable Offline
Cloud Gazer

Registered: 23/12/2004
Posts: 23
Loc: Narangba
That explanation was a big help, thankyou Ken smile

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#1490764 - 17/02/2019 21:47 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Ken Kato Offline
Meteorological Motor Mouth

Registered: 05/03/2012
Posts: 6090




No worries smile

Just to add to my previous post, above are a couple of examples of how ensembles give an idea of how much or little uncertainty there is for various things such as TC tracks.
The 1st image is of TC Iris and shows a huge spread of potential tracks from various ensembles which implies high uncertainty due to competing steering influences.
The 2nd image is of TC Marcus which shows all tracks tightly clustered together which implies low uncertainty.

In both cases, black = the actual track that eventuated. The forecast tracks go out to 10 days from the observed position (where the TC's name tag is).

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#1490779 - 18/02/2019 04:40 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
james1977 Offline
Weatherzone Addict

Registered: 16/11/2009
Posts: 2946
Loc: collingwood park
Watl has kicked up the rainfall totals a bit with a wide area of 50-100mms . Best outlook Iíve seen for this area for sometime
_________________________
I hate winter

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#1490782 - 18/02/2019 07:48 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Flowin Offline
Weather Freak

Registered: 15/10/2017
Posts: 966
Loc: Pinjarra Hills, Qld
I think WATL (PME) which is an based on eight models (2 Australian, and 6 international) is this morning biased to the high side due to the ECMWF forecast. Unfortunately all other models are not showing much rain for SEQ for the next seven days. If ECMWF proves correct that may be good for some much needed rain, but also not good for it impacts on large waves and beach damage.


Edited by Flowin (18/02/2019 07:49)

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#1490793 - 18/02/2019 09:17 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
retired weather man Offline
Meteorological Motor Mouth

Registered: 01/07/2007
Posts: 5161
Loc: Wynnum
WYNNUM NORTH ( 27.4S 153.2E ) - WEATHER

DATE..18 FEB 2019 TIME..0815

CURRENT TEMPERATURE......26.5C
CURRENT HUMIDITY...........61%
CURRENT DEW POINT......... 18C
CURRENT WIND DIR/SPEED... S 4kph
CURRENT MSLP PRESSURE....1012.3Hpa
CURRENT VISIBILITY........30KM
CURRENT WEATHER...........3/8 cloud.
RAIN SINCE 0900 SUNDAY....0.0mm

LAST 24 HOURS -
YESTERDAY'S MAX TEMP.......31.4C
THIS MORNING'S MIN TEMP....18.6C
THIS MORNING'S GRASS MIN...17.1C
AVERAGE 24 HOUR DEW POINT....16C
AVERAGE 24 HOUR MSLP.......1012.8Hpa
LAST 24 HOUR MAX WIND GUST..E 44kph at 1125
PAST 24 WEATHER SUMMARY... No significant weather..

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#1490811 - 18/02/2019 14:22 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Locke Offline
Weatherzone Addict

Registered: 27/12/2007
Posts: 4553
Loc: Brisbane
Posted this in the Oma thread but pertinent here.

I can already see surge being a problem in SE QLD irrespective if whether Oma makes landfall or not.

This morning's high tide at the Brisbane Port gauge was already close to Minor Flood level with Oma still over 1,000km away.

Tide gauges are already showing up to 15cm over normal tide levels and this will only increase as Oma gets closer to the Australian mainland. I would be surprised if surge doesn't exceed half a metre at a minimum even if Oma stays well offshore, higher if she gets closer.

Add this to the already very high tides forecast for the end of the week and massive seas and you have a recipe for some coastal inundation and severe beach erosion.

Depending on tomorrow mornings tides I would hope that coastal councils start making sandbags available soon.
_________________________
This post and any other post by Locke is NOT an official forecast & should not be used as such. It's just my opinion & may or may not be backed by sound meteorological data. For official information, refer to Australian Bureau of Meteorology products.

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#1490813 - 18/02/2019 14:38 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Stormwalker Offline
Weather Freak

Registered: 13/11/2013
Posts: 96
Would the tide this morning be a result of the supermoon (not the cyclone).

Or is the point you are making is that the tides are higher than the usual king tide.

I only ask, because I vaguely recall a few years ago a king tide caused minor flooding in places (I thought around breakfast creek) without any other weather event influencing it.

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#1490818 - 18/02/2019 15:30 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Mike Hauber Offline
Weatherzone Addict

Registered: 13/07/2007
Posts: 3817
Loc: Buderim
Oma has a pretty large circulation at the moment which increases storm surge potential, but it does shrink down as it comes towards the coast. Still a fair size I think. On the other hand winds are rather parrallel to the coast which I'd think would mean much less storm surge threat unless it does get all the way to the coast.

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#1490820 - 18/02/2019 15:43 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
Ken Kato Offline
Meteorological Motor Mouth

Registered: 05/03/2012
Posts: 6090





Above are the forecast sea level anomalies and surface currents for today compared to the upcoming Sunday generated by the OceanMaps system (the surface winds are forced by ACCESS-G).

You can clearly see the storm surge type effects along the coast in the 2nd map although the degree to which this occurs depends on ACCESS-G's current scenario being close to reality (which currently has a long fetch of vigorous southeasterlies pushing up against the coast after it starts pushing Oma/ex-Oma back up north).

You can also see that sea level is a bit higher than normal already at the moment which is adding to the high tides.

That anticyclonic eddy off the coast with the associated significant high sea level anomaly (which is typical of anticyclonic eddies) also shows up well.

BTW thanks for posting the Bureau's special climate statement the other day Flowin. Pertinent to note the "The highest weekly accumulations were comparable in terms of geographic spread, duration, and intensity of rainfall to those of January 1998 and January 1953" bit in it as well.

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#1490821 - 18/02/2019 15:44 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Stormwalker]
Flowin Offline
Weather Freak

Registered: 15/10/2017
Posts: 966
Loc: Pinjarra Hills, Qld
Originally Posted By: Stormwalker
tide this morning be a result of the supermoon (not the cyclone).

That would be factored into the base level astronomical tide predictions which are predicted and published well in advance.

King tide is a lay term that is not readily aligned to scientific principles of analysis of tides.

My understanding of storm surge tides (amount of tide rise above the predicted astronomical tide) is that there are a number of components to it including a rise component due to low pressure, a rise component due to wind shear (wind pushing water against the coast) and a rise component due to wave setup (the incoming large waves can't drop enough before the next wave) for which reefs and shape of seabed play an important role.
So even if the low pressure centre stays away, the potential for surge due to wind shear and wave setup alone may be significant.

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#1490829 - 18/02/2019 16:21 Re: SEQLD / NENSW Day to Day Weather - January to July 2019 [Re: Seabreeze]
gleno71 Offline
Weatherzone Addict

Registered: 09/11/2007
Posts: 1868
Loc: Australia
Is it fair to say that we are simply confusing ourselves with all these different models and what the potential outcome will be ?

If you go back 5-10 years ago on this forum, there was more straight forward and less confusing talk, maybe that's because there were less models provided?

Though I do look at windy, it's only 1 model. A lot of people look at that and swear by it.

On the radio this morning, Ken Brown from Brownies coast watch stated " I regularly keep in contact with the senior forecaster from the BOM, they only forecast on 5 MAIN MODELS " 3 european models and 2 Australian Access Models


I would to hear Ken Kato's thoughts on these 5 models and if we need to look at other Models even if they are freely available..

Cheers..

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