Tropical Depression Dorian

[Ed Lizard]

What "people who are going gangbusters on a FL threat?" You mean elsewhere (S2K, etc)? Certainly not here...if you mean here, you're creating a strawman. 

 

Heck, people here who fairly mildly argue that it isn't going to weaken, or may intensify, sometimes feel compelled to apologize for seeming like a weenie in their own posts.

 

People here have been mostly anti-weenie-ing this thing into oblivion using an armada of sophisticated arguements since it was a wave over Africa, and it's consistently been STRONGER "than many people may expect" up until now. Of course, this doesn't mean it DOESN'T weaken or dissipate over the next few hours or days; I just don't see where the predominance of opinion on Dorian has been some sort of ill-informed weenie hype.

 

American (and Eastern) are a lot different than they were years ago. I actually think there's more bias and inaccuracy now from people trying to be "cooler than thou" by proclaiming the bust or demise of (insert TC/outbreak/snowstorm here) than from over-excited weenies. And it's actually a bit more insidious in some respects because the former is more likely to come from Red taggers, and at least SEEM more informed and well argued, than the latter.

 

People almost feel compelled to invent weenie strawmen so they can look cool debunking them.

 

 

 

 

I embraced my inner weenie on the GFS on this last week, partly because despite the talk of MJO phase, I actually saw a negative OLR anomaly in the Central Pacific Atlantic when looking at something I posted in the Eastern Pacific thread.

 

Everyone knows I lean a tad weenie, I'm glass half full optimistic, but the too cool for school it is going to die thing, that may be true, but while the GFS hasn't been perfect, the Euro didn't really even see a closed tropical low until the closed tropical low had formed.

 

BTW, tracks, checking 0Z Euro ensembles and 12Z GFS ensembles, where Dorian goes, if it survives, a mystery.

 

4 people posted while I typed this...

 

 

[It's Always Sunny]

Chill out Derecho.

[thewxmann]

GFS became #1 for me after Debby last year. ECMWF had a hurricane into Houston, GFS had a tropical storm into FL. Since that time, the GFS has consistently performed better and it continues today. Last time I checked the ECMWF was never showing a 60mph tropical storm on any of its runs last week. And just because the GFS is an outlier on intensity does not mean its solution is incorrect. When you're the best model, you tend to be an outlier until the laggers catch up.

 

And how did the GFS do with Sandy? Or the tropical waveicane that followed Chantal? 

[It's Always Sunny]

Ed, where did you get the Euro ensemble forecast track?

[Ed Lizard]

And how did the GFS do with Sandy? Or the tropical waveicane that followed Chantal? 

The Euro ten day forecast, out when Sandy was forecast to be past Cuba and approaching the Bahamas, was amazing.  It showed the trough that would capture Sandy extending downward in such a way it was easy to picture a capture.  I was so weenied about that, I posted it in the NYC subforum, so the hard core tropical people wouldn't mock me.

 

That said, are boguscanes worse than not seeing a TC from 2 days away?

[Ed Lizard]

Ed, where did you get the Euro ensemble forecast track?

http://www.emc.ncep.noaa.gov/gmb/jpeng/TC_ens_V1.html

[IsentropicLift]

Maybe it's just me but Dorian looks just fine right now. Nice burst of deep convection on the western side and looking more symetrical with good outflow

 

[phil882]

This is an awesome site. Exactly what I was looking for. Thanks man. I'm assuming this is the new GFS as well...

 

Yep... the usual distribution sites should now be using the feed from the new supercomputer. Its worth emphasizing again that this is the same version of the GFS, but has been recompiled to run on the new WCOSS. Dtk outlined these changes in an earlier post. The differences you see with this version of the GFS are random error and not systematic changes that occurred within the model framework. 

[gulfcane]

Improvement

[phil882]

Maybe it's just me but Dorian looks just fine right now. Nice burst of deep convection on the western side and looking more symetrical with good outflow

 

This is the problem... the IR appearance is superficial when the llc is displaced west of the deepest convection and is battling dry air entrainment from the west. 

 

[atownwxwatcher]

 

Dorian actually looks better now then it has all day... 

 

[wxmeddler]

It might be better at this point for Dorian to cut itself loose from feeding on the ITCZ high PW band and try to work on its own by closing itself off. GFS has this happening around 50W in 48 hrs.

[mimillman]

No changes on 5PM advisory.

[TropicalAnalystwx13]

This is the problem... the IR appearance is superficial when the llc is displaced west of the deepest convection and is battling dry air entrainment from the west. 

 

"IN ADDITION...A 1728Z TRMM OVERPASS INDICATED A

NEARLY CLOSED LOW-LEVEL EYE HAD DEVELOPED BENEATH A WEAK MID-LEVEL

EYE FEATURE. SATELLITE CURRENT INTENSITY ESTIMATES REMAIN AT 55 KT

AND 45 KT FROM TAFB AND SAB...RESPECTIVELY...AND AN EARLIER ASCAT-B

OVERPASS AT 1230Z INDICATED SURFACE WINDS OF AT LEAST 48 KT NORTH

OF THE CENTER."

[phil882]

"IN ADDITION...A 1728Z TRMM OVERPASS INDICATED A

NEARLY CLOSED LOW-LEVEL EYE HAD DEVELOPED BENEATH A WEAK MID-LEVEL

EYE FEATURE. SATELLITE CURRENT INTENSITY ESTIMATES REMAIN AT 55 KT

AND 45 KT FROM TAFB AND SAB...RESPECTIVELY...AND AN EARLIER ASCAT-B

OVERPASS AT 1230Z INDICATED SURFACE WINDS OF AT LEAST 48 KT NORTH

OF THE CENTER."

 

This would be what Stewart was looking at. The low-level circulation is well organized, but its obvious the mid-level center is tilted NE of the low-level vortex (note where the deepest convection on this image is located).

 

[Ground Scouring]

A question: if Dorian at 120 hours were near the NHC forecast position, approximately how deep would it need to be in order to reduce the southwesterly shear imparted by the upper low? I know that particularly vigorous convection can warm the upper troposphere sufficiently so as to destroy a weak TUTT in front of the system. In this case, there will be 30-40 kt of shear but the TUTT appears to be fairly week on day five. Dorian, if sufficiently deep, could induce a large-enough anticyclone to reduce the net shear. I don't expect Dorian to survive but am interested in how such a scenario would evolve if Dorian *did* persist.

[Snow_Miser]

Levi Cowan just posted this to Tropical Tidbits on Facebook:

 

"Dorian continues to impress today, passing over the coldest water of its journey with flying colors, and now firing the deepest convection of its lifetime to date. The storm also appears to have turned more towards the west, which was expected at some point. Dorian has gone from a storm anticipated to struggle for its life to one that is now likely to remain intact and strengthen down the road."

[wxmeddler]

A question: if Dorian at 120 hours were near the NHC forecast position, approximately how deep would it need to be in order to reduce the southwesterly shear imparted by the upper low? I know that particularly vigorous convection can warm the upper troposphere sufficiently so as to destroy a weak TUTT in front of the system. In this case, there will be 30-40 kt of shear but the TUTT appears to be fairly week on day five. Dorian, if sufficiently deep, could induce a large-enough anticyclone to reduce the net shear. I don't expect Dorian to survive but am interested in how such a scenario would evolve if Dorian *did* persist.

The same question was asked on Wunderground and Levi Cowan from Tropical Tidbits answered it pretty well. See post #981

[AutoPenalti]

Levi Cowan just posted this to Tropical Tidbits on Facebook:

"Dorian continues to impress today, passing over the coldest water of its journey with flying colors, and now firing the deepest convection of its lifetime to date. The storm also appears to have turned more towards the west, which was expected at some point. Dorian has gone from a storm anticipated to struggle for its life to one that is now likely to remain intact and strengthen down the road."

Gotta love my storm.

[wxmeddler]

18z GFS makes Dorian do the the Hispaniola split.

[phil882]

Yea I'm definitely not sold that this is a "storm likely to remain intact." Convection should probably continue to pulse, but per the earlier morning discussion in this thread, the GFS might be overemphasizing how large the TC is. The convective structure is nowhere near as large (or organized) as what the GFS has been depicting. The storm was better organized yesterday embedded in the CDO. Today it looks more like a sheared TC with a tilted structure that is worsening with time. I'm less optimistic than yesterday that this is a storm that will make it to the Lesser Antilles as a TC.  

[bluewave]

Yea I'm definitely not sold that this is a "storm likely to remain intact." Convection should probably continue to pulse, but per the earlier morning discussion in this thread, the GFS might be overemphasizing how large the TC is. The convective structure is nowhere near as large (or organized) as what the GFS has been depicting. The storm was better organized yesterday embedded in the CDO. Today it looks more like a sheared TC with a tilted structure that is worsening with time. I'm less optimistic than yesterday that this is a storm that will make it to the Lesser Antilles as a TC.  

 

We may see at least a partially exposed low level circulation west of the main area of convection with the first visible images tomorrow morning.

[TropicalAnalystwx13]

I think we should see some recovery in the convective appearance of Dorian as the storm enters DMAX in a few hours. That's how it's been the past few days.

[Ed Lizard]

I still just wonder, new computer, and op 12Z and 18Z GFS would be on the extreme Southern end of 0Z ensembles...

 

Seems so sudden...

 

 

The smart(er) models do keep it steady state or weaken it, looking at 18Z BAM guidance, weaker would be farther South, so maybe 12Z and 18Z GFS op are onto something

 

[It's Always Sunny]

I agree. I don't think we'll really know till these models experience more extreme weather events. One thing I know for sure is that we will remember how the GFS was playing this storm out before we switched to the WCOSS.

[SBUWX23]

The model physics have not changed yet.  The model has just been reconfigured to run on a bigger/faster machine.  I do not think we will see any major changes from the supercomputer until the actual physics/assimilation change.  Someone can correct me if I am wrong here, however.

I still just wonder, new computer, and op 12Z and 18Z GFS would be on the extreme Southern end of 0Z ensembles...

 

Seems so sudden...

 

 

The smart(er) models do keep it steady state or weaken it, looking at 18Z BAM guidance, weaker would be farther South, so maybe 12Z and 18Z GFS op are onto something

 

[It's Always Sunny]

I would read this article. It touches on some good points about the CCS vs. WCOSS.

 

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/25/new-weather-service-supercomputer-faces-chaos/

[SBUWX23]

thanks for the link!

I would read this article. It touches on some good points about the CSS vs. WCOSS.

 

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/25/new-weather-service-supercomputer-faces-chaos/

[gulfcane]

The model physics have not changed yet.  The model has just been reconfigured to run on a bigger/faster machine.  I do not think we will see any major changes from the supercomputer until the actual physics/assimilation change.  Someone can correct me if I am wrong here, however.

There are differences. As noted from the WCOSS site:

 

Differences in Model System Solutions

We have made every effort to make the WCOSS and CCS solutions as close as possible to each other. However, there should not be an expectation that the WCOSS and CCS solutions will be the same. There are several contributors to differences in the solutions.

1. The numerical round-off and order of calculation is different between the two machines. So when two numbers are multiplied together or any other arithmetic operation, the results will be slightly different. These differences can then grow non-linearly in the forecast and in the assimilation system.
2. The input observation databases will not be identical since they are created independently. Due to small timing differences in the creation of the databases and communication speeds on the CCS and WCOSS machines, there may be slightly different data being used in the two systems.
3. In the process of converting to the new computational infrastructure, some bugs were discovered. These bugs did not appear to have much impact (or in most cases any impact) on the CCS, but some had very severe impact on the stability or results on the WCOSS machine. Obviously, we had to fix these results which can result in small changes in the results.
4. Some IBM power series functions were being used on the CCS (for example FFTs, and random number generators). These functions were not available on the WCOSS machine and substitutes were created. These substitutes produce similar results, but not identical.

For all of these reasons, the forecasts will not be identical and the differences have the potential to be more different the longer the assimilation systems are run independently and for longer term forecasts. We continue to monitor the systems to minimize the possibility that a real error in the transition to the new machine will occur, but since the results will naturally be different, it is not possible to perform a definitive test. I will note that there have been several problems with the NCO WCOSS parallel. These problems have occurred when there were machine problems, the parallel was switched from one machine to another and when files were not properly supplied to the systems. When the problems occur and are fixed NCO has been restarting the parallel from the CCS results. NCO is making every effort to eliminate these issues, but it is important that the evaluators do not waste their time on forecasts created when a problem exists. Because of the expected differences, we do not believe that you should be worried about changes in individual forecasts, but rather about systematic differences between the two systems which may indicate a problem in the conversion. We appreciate your evaluations of the two systems and appreciate notification of any systematic differences as soon as possible so that any potential problem can be diagnosed and if necessary fixed in the WCOSS parallel.

 

[Derecho!]

 

The smart(er) models do keep it steady state or weaken it, looking at 18Z BAM guidance, weaker would be farther South, so maybe 12Z and 18Z GFS op are onto something

 

 

 

I'd point out that while the GFDL and HWRF are "smarter" in that they are far more computationally sophisticated than the relatively primitive LGEM and DSHIPs, the latter two models have been GREATLY superior in intensity forecast accuracy at later (96 and 120 hour)  time periods than the GDFL and HWRF.

 

They've been so bad, I'd almost take the fact that the GFDL, and the HWRF (mostly) have the system so weak at 120 hours as evidence that it will actually be quite robust.