ATL: Ex-DANIELLE - Models

[KWT]

It's not just one run of any model...again it's the trend.

Yesterday, the GFS, Euro and others had a gigantic trough over the western Atlantic and a huge hurricane-like feature weakening the ridge...from the north over the central Atlantic.

Last night, the GFS was still on that idea, but the Euro left some ridging behind and trapped the cyclone out to t+240

Today, the GFS no longer develops the north Atlantic hurricane feature...and the Euro is even stronger with the W Atlantic ridge than it was last night. The GFS leaves more ridging in the west Atlantic too..

The models are going to change, again, I assure you of that.

But watch the trend...and right now the trend is away from gigantic trough and strange looking upper disturbance weakening the ridge.

We, of course, have no choice but to keep watching...but I would suggest stop looking at any specific model track in the extended, and look at the trend toward how the steering features are developing in the models.

MW

Ok a few things....firstly the ECM is very different from last nights run and even the 0z ECM, the simple reason it doesn't recurve is because its barely a closed low on the 12z run...

http://www.ecmwf.int/products/forecasts ... !chart.gif

Trough is still there at 192hrs as you can see...BUT the system is so weak it sails on by. Now that trough isn't all that deep so it won't recurve it totally but you'd probably see a hurricane get upto 30N as the GFS does and once you get that north only a full lbown upper high over Canada will lead to a threat.

However your right and it is very easy to get caught up in the individual runs...all I will say is for now it is just 1 run...all other models still have this gaining more then enough latitude before 168hrs to make no difference what the upper high does between 8-10 days out.

I do sense the tide turning though and the longer this takes to get going the higher the risk of this hitting land.

[ConvergenceZone]

If this EURO 500 is right, this is GOM bound.

Wx_Warrior, be careful with that comment, otherwise before you know it
some people will read too much into your post and pretty soon there will be a
texas vrs florida war going on, LOL....

[Dean4Storms]

It's not just one run of any model...again it's the trend.

Yesterday, the GFS, Euro and others had a gigantic trough over the western Atlantic and a huge hurricane-like feature weakening the ridge...from the north over the central Atlantic.

Last night, the GFS was still on that idea, but the Euro left some ridging behind and trapped the cyclone out to t+240

Today, the GFS no longer develops the north Atlantic hurricane feature...and the Euro is even stronger with the W Atlantic ridge than it was last night. The GFS leaves more ridging in the west Atlantic too..

The models are going to change, again, I assure you of that.

But watch the trend...and right now the trend is away from gigantic trough and strange looking upper disturbance weakening the ridge.

We, of course, have no choice but to keep watching...but I would suggest stop looking at any specific model track in the extended, and look at the trend toward how the steering features are developing in the models.

MW

That and climatogical aspects have to be weighed here. Last nights runs had basically a huge Nor'Easter for the NE Coast with that storm they depicted, I just don't see it for late August. True we can get a trough dropping down this time of year, but this scenario was completely collapsing the ridge in the Atlantic to well east out east of the central Atlantic, that makes no sense. If it was late Sept or Oct. OK!

[Dean4Storms]

It's not just one run of any model...again it's the trend.

Yesterday, the GFS, Euro and others had a gigantic trough over the western Atlantic and a huge hurricane-like feature weakening the ridge...from the north over the central Atlantic.

Last night, the GFS was still on that idea, but the Euro left some ridging behind and trapped the cyclone out to t+240

Today, the GFS no longer develops the north Atlantic hurricane feature...and the Euro is even stronger with the W Atlantic ridge than it was last night. The GFS leaves more ridging in the west Atlantic too..

The models are going to change, again, I assure you of that.

But watch the trend...and right now the trend is away from gigantic trough and strange looking upper disturbance weakening the ridge.

We, of course, have no choice but to keep watching...but I would suggest stop looking at any specific model track in the extended, and look at the trend toward how the steering features are developing in the models.

MW

Ok a few things....firstly the ECM is very different from last nights run and even the 0z ECM, the simple reason it doesn't recurve is because its barely a closed low on the 12z run...

http://www.ecmwf.int/products/forecasts ... !chart.gif

Trough is still there at 192hrs as you can see...BUT the system is so weak it sails on by. Now that trough isn't all that deep so it won't recurve it totally but you'd probably see a hurricane get upto 30N as the GFS does and once you get that north only a full lbown upper high over Canada will lead to a threat.

However your right and it is very easy to get caught up in the individual runs...all I will say is for now it is just 1 run...all other models still have this gaining more then enough latitude before 168hrs to make no difference what the upper high does between 8-10 days out.

I do sense the tide turning though and the longer this takes to get going the higher the risk of this hitting land.

Sorry KWT, simply because it is a weaker system is not the only reason for the no recurve in the 12z ECM, look at the ridging to its north. Not even a Cat. 5 is going to bust through that!!

[KWT]

The ridging is pretty weak at the upper levels Dean, the ridging is there on the 12z ECM but really a strong hurricane would probably end up at 30N instead of 20N...which may not sound like much but it makes the world of difference in terms of what is possible from there down the line.

Now a weaker system though would find the exit door slammed shut on the ECM, the trough isn't as deep thats for sure on the 12z ECM.

My punt for the 18z GFS...its a good bit further west then the 12z run.

[ColinDelia]

I still think it is to premature on "fish" vs "no fish".

1. We don't even have a depression yet and where and especially when one forms has some bearing on the question.
2. Intensity forecast errors of tropical cyclones are the Achilles' heal of prediction. This is still just an "elongated area of low pressure" and the error is even higher.
3. I said when and where it forms. Dare I even say it? "If!"

Just this year we can see how difficult even a 48 hour forecast can be for an "elongated area of low pressure". Remember the "other Danielle"?

If you held a gun to my head and make me choose I'd say "fish" but fortunately I'm just sitting here eating some beef jerky and drinking a Diet Pepsi minding my own business. No gun in sight.

[Dean4Storms]

Well I see your point in the difference there KWT, much might depend on the strength of the storm, but with our experience so far this year on storms strengthening much the ECM might be onto something.

[Dean4Storms]

I still think it is to premature on "fish" vs "no fish".

1. We don't even have a depression yet and where and especially when one forms has some bearing on the question.
2. Intensity forecast errors of tropical cyclones are the Achilles' heal of prediction. This is still just an "elongated area of low pressure" and the error is even higher.
3. I said when and where it forms. Dare I even say it? "If!"

Just this year we can see how difficult even a 48 hour forecast can be for an "elongated area of low pressure". Remember the "other Danielle"?

If you held a gun to my head and make me choose I'd say "fish" but fortunately I'm just sitting here eating some beef jerky and drinking a Diet Pepsi minding my own business. No gun in sight.

[Ivanhater]

What a difference 24 hours makes....Looking at the ridging

12z yesterday



12z today

[Macrocane]

It's interesting that both the Pacific and the Atlantic systems are weaker today, still on the very long range so I wouldn't be surprised to see another big change in the pattern and the intensity of the systems tonight.

[KWT]

In terms of placement of that system Ivanhater and the strength really couldn't be much different even if it tried!

[ColinDelia]

240 hours is too far out IMO. The models don't get the position of the troughs and ridges all that well past 180 hours. An anomaly correlation of 0.6 is generally regarded as an indication of a useful forecast and at .6 it has been observed by researchers that the troughs and ridges are generally in about the right place.

Recent data shows that the anomaly correlation of .6 for the GFS occurs around 7.5 days = 180 hours
http://www.emc.ncep.noaa.gov/gmb/STATS/ ... .2009.html

[KWT]

Interesting ColinDelia, but most of the models are well on there way northwards by that time...the differences between the ECM and the GFS and the others actually kick in as early as 120hrs.

Just looking at the eCM ensemble mean, they are weaker with the troughing on the 12z runs compared to the 00z but thats only out to 120hrs, will be interesting to see how far west they also shift if at all.

[gatorcane]

18Z GFS running.......

[KWT]

18z ECM ensembles suggests a very tight situation with quite a few recurving based on the means but also some taking it further west. If it sticks around 25N by 216hrs the pattern suggests it'd be forced westwards on the ECM means...if not then the trough is stronger then what was suggested by the op run so would probably be enough in the tank to recurve.

[KWT]

18z GFS keeps a double Vort structure by 42hrs:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... v_042m.gif

[ConvergenceZone]

Hmmm, I wonder if the GFS is going to go weaker this round...
Maybe the trend will be a weaker more westward storm?

It would be something if this didn't develop at all. That probably is not the case, but I wouldn't rule it out.

[KWT]

It is strengthening at least through 54hrs though the other Vort system is also pretty obvious rotating around the main circulation...

Whether or not the NHC would be prepared to upgrade if something like that happened I have no idea!

[ColinDelia]

Interesting ColinDelia, but most of the models are well on there way northwards by that time..

True and the basic setup by 180 hours is probably about right - as far as the ridges and troughs. As far as the track a tropical cyclone takes we do have the "cone" to understand that error in distribution. For the NHC official forecast for a tropical cyclone the 5 year error at 120 days is 250 nm. But what is the error for "an elongated low"? Certainly much higher than that. And what is the forecast error at, say, 180 hours for an "elongated area of low pressure"? There's a reason why we only get a 5 day forecast from the NHC.

As can be seen here the NHC official forecast tends to be better than any individual model.
http://www.nhc.noaa.gov/verification/verify6.shtml

5 year Average NHC forecast errors
http://www.nhc.noaa.gov/verification/pd ... erages.pdf

[KWT]

You can see the 2nd vortex still being thrown around the larger and stronger circulation at 72hrs:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... v_072m.gif

Thats probably not the most condusive set-up to have if you want a quickly developing system though...moving WNW already at 72hrs.

Oh and troughing looks weaker as well so far...