TD #4 East Atlantic,Comments,Sat Pics,Models Thread #2

[Air Force Met]

Look what is coming behind TD 4. It is HUGE. The GFS has been showing it for a couple of day. It now has a good satellite presentation.

Sat Image

Take a look at the size of the 850mb circulation...

AFM, would you say, judging by that pic, that the train has definitely "left the station"?

Getting there.

[benny]

I ALLLMOST made a post earlier tonight that it would be interesting to see what happens when polar opposites take succeeding forecast shifts: "Mr. Conservative" Franklin vs. "Bust the Envelope, Out of the Box" Stewart. Wish I had the time to do that.

And yep, tropical weather fans are not dissapointed.

The breakdown of the subtropical ridge in all of the modeling seems suspect...as it is occuring from the bottom side as opposed to erosion from shortwaves to the north.

But it is hard to see exactly what features are conspiring to bust down the ridge bottomside-up using the vapor imagery or the limited weather data.

In the end this is probably going to run NW into the open Atlantic...but I would venture to guess mr Stewart would have liked to shove the track even further west...but forecasting procedures won't allow that.

Look...I have ALWAYS said Stacy should start the first 2 or 3 forecasts on every system. He takes everything into account and doesn't bow to the will of the modeling.

These forecasts...with systems in the eastern Atlantic where the upper features are simply not observed well...are the hardest to make.

MW

"Bow to the will of the modeling"... why do you think the forecasts have improved over the past 20 years so much??? Only one thing... numerical models. Forecasters can add some value but the decrease in track error almost perfectly mirrors the improvement in guidance. There is a reason why in general no one moves far from the model consensus anymore.. it is tough to beat on a regular basis. Just because a feature is hard to see doesn't mean it isn't there. Models aren't perfect.. but you better have a darn good reason to stray too far off track...

[MWatkins]

I ALLLMOST made a post earlier tonight that it would be interesting to see what happens when polar opposites take succeeding forecast shifts: "Mr. Conservative" Franklin vs. "Bust the Envelope, Out of the Box" Stewart. Wish I had the time to do that.

And yep, tropical weather fans are not dissapointed.

The breakdown of the subtropical ridge in all of the modeling seems suspect...as it is occuring from the bottom side as opposed to erosion from shortwaves to the north.

But it is hard to see exactly what features are conspiring to bust down the ridge bottomside-up using the vapor imagery or the limited weather data.

In the end this is probably going to run NW into the open Atlantic...but I would venture to guess mr Stewart would have liked to shove the track even further west...but forecasting procedures won't allow that.

Look...I have ALWAYS said Stacy should start the first 2 or 3 forecasts on every system. He takes everything into account and doesn't bow to the will of the modeling.

These forecasts...with systems in the eastern Atlantic where the upper features are simply not observed well...are the hardest to make.

MW

"Bow to the will of the modeling"... why do you think the forecasts have improved over the past 20 years so much??? Only one thing... numerical models. Forecasters can add some value but the decrease in track error almost perfectly mirrors the improvement in guidance. There is a reason why in general no one moves far from the model consensus anymore.. it is tough to beat on a regular basis. Just because a feature is hard to see doesn't mean it isn't there. Models aren't perfect.. but you better have a darn good reason to stray too far off track...

100% agree there. CONU and GUNA consistently rank right up there...and this forecast is not that disparate from the last one. I think what I am going for is that Stacy is open and willing to entertain and discuss ideas that may not be supported by the modeling. Not that JF isn't...but typically only Stacy and maybe Dr Beven are willing to get those ideas out there.

But then again...the models have shown a consistent northward bias in situations like this...deep tropical systems way out in the Atlantic. See Frances and Jeanne and even Ivan early in their lifetimes for examples. While overall the models win...especially the consensus...I think it would be an interesting study to compae climo to the models...homogeneously...in these situations to see which wins. Afterall...there has to be a reason why LBAR is a good performer in the deep tropics...

MW

[temujin]

Well, in this specific instance, Stewart has the advantage of time. For a while today, TD 4 looked like it was going NW. But now, looking back with the advantage of more time, we see that it's been going more W. Stewart also mentioned that the ridging is building further west.

I don't see Stewart as having taken that much of a gamble. He's just admitting the models just haven't gotten this one right yet.

[GeneratorPower]

Mike, what do you see that makes this TD#4 different from, say, Ivan. I think it's a bit farther east and north than Ivan was. Synoptically, any major differences?

[Jim Cantore]

hmm, if that projected track pans out, and it heads NW then bends back WNW or W, I might have something to watch.

[Matt-hurricanewatcher]

The quickscat shows only 30 knot winds...With a well defind LLC. Dry air seems to have killed all the outter convection. While there is some convection forming near the cetner. Right now is do or die for this system. Why because if it can't form a inner core now it will move into strong SAL...As it moves more westward or northward.

For right now
30 knots
6 30 knots
12 35 knots?
24 40 knots
36 45 knots
48 50 knots
60 55 knots
72 55 knots

For one this could be way to high if the dry air kills the convection any more tonight. If it can get its act together it could be about this or slightly higher.

[MWatkins]

Mike, what do you see that makes this TD#4 different from, say, Ivan. I think it's a bit farther east and north than Ivan was. Synoptically, any major differences?

Actually, Ivan is probably a bad example. Westward movement was more or less a foregone conclusion at the first advisory...your analysis is right on...TD4 is further east and north:

http://www.nhc.noaa.gov/archive/2004/di ... .001.shtml?

Frances is a better example:

Advisory 1:
http://www.nhc.noaa.gov/archive/2004/di ... .001.shtml?

Advisory 2:
http://www.nhc.noaa.gov/archive/2004/di ... .002.shtml?


Jeanne is also a bad example in retrospect...as there were issues with intereaction with Ivan...and of course it developed much further west:

http://www.nhc.noaa.gov/archive/2004/di ... .002.shtml?

So then I guess only Frances is a good example of this...but then again this type of way far east development doesnt happen very often.

MW

[GeneratorPower]

Mike, what this is telling me (with those Frances advisories) is that there was a NW turn forecasted, into a weakness in the Subtropical or Midtropical Ridge, that never materialized. Of course, Frances struck the FL East Coast so it did indeed turn NW, but it didn't recurve.

What I'm reading in these discussions is that they thought it might turn more than it actually did.

[GeneratorPower]

If 2005 taught us anything, it should have taught us to remember the NHC's favorite disclaimer:

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 225 NM
ON DAY 4 AND 300 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY

Those numbers are averages. Sometimes lower (I.E., the Katrina forecast), sometimes higher. Sometimes MUCH higher. We just don't know what this is going to do.

[crab_storm]

fish

[Regit]

fish

Why?

[the_winds_that_sheared_me]

Mike, what this is telling me (with those Frances advisories) is that there was a NW turn forecasted, into a weakness in the Subtropical or Midtropical Ridge, that never materialized. Of course, Frances struck the FL East Coast so it did indeed turn NW, but it didn't recurve.

What I'm reading in these discussions is that they thought it might turn more than it actually did.

Here was how the forecasts changed Graphically, Click the 5 day forecast button on the left-the default is 3day. http://www.nhc.noaa.gov/archive/2004/FR ... hics.shtml

[crab_storm]

obvious steering currents

[GeneratorPower]

fish

Grouper, Red Snapper, Catfish, Trout, Crappie, Flouder, Swordfish, Mahi-Mahi, Sea Bass...

[btangy]

The seeds to the weakness in the ridge that all the models seems to be latching onto are already planted:

Here's the height of the dynamic tropopause in potential temperature coordinates as analyzed by the 18Z GFS:

http://www.atmos.albany.edu/facstaff/rm ... 082118.jpg

If one is not familiar with PV/tropopause maps, the 200mb vorticity from CIMSS shows a similar feature:

http://cimss.ssec.wisc.edu/tropic/real- ... g8vor1.GIF

There's a large positively tilted 'PV tail' extended down from the mid-latitudes that is the source of all these upper level lows you see spinning around in the W Atlantic.

The 72 hour prog 18Z GFS shows the PV tail fragmenting which each magenta region representing an upper level low:

http://moe.met.fsu.edu/tcgengifs//gfs/2 ... 50PV12.png

The anomaly in the C Atlantic is projected to be quite strong and deep, so that its mid-level reflection will provide enough of a weakness in the ridge to eventually pull TD 4 north if it strengthens and becomes a deeper system. You can see this in the 500mb vorticity at 120hours for example @ ~55W,27N:

http://moe.met.fsu.edu/tcgengifs//gfs/2 ... vort20.png

All of the GFS ensemble members, even in the S portion of the ensemble envelope spread forecast recurvature:

http://wind.mit.edu/~btangy/TC/fig/storm1_18_ms3.png

[crab_storm]

http://www.skeetobiteweather.com/picser ... p?t=m&m=04

pretty much all in agreement

[willjnewton]

will tropical depression four likely to affect the east coast in the next couple of weeks??like is it possible??like what does the latest global forecast models take this system After 144 hours, do they recurve the system as being more fish or do they have it taking a more Westward track, like the national hurricane center has it???please explain okay, thankyou

[the_winds_that_sheared_me]

http://www.skeetobiteweather.com/picservice.asp?t=m&m=04

pretty much all in agreement

From the NHC 11pm Discussion:

THE GLOBAL MODELS...AS WELL AS THE GFDL
AND THE BAM MODELS...REMAIN TIGHTLY CLUSTERED AND IN EXCELLENT
AGREEMENT ON AN IMMEDIATE NORTHWESTWARD MOTION. UNFORTUNATELY...
THE MODELS HAVE ALSO BEEN EXCELLENTLY WRONG THUS FAR. TD-4 IS
CURRENTLY AT LEAST 60 NMI SOUTHWEST OF THE 18Z GFS FORECAST
POSITION FOR 22/00Z...AND THE OTHER MODELS ARE SIMILARLY TOO FAR TO
THE NORTHEAST OF THE CURRENT POSITION. AS A RESULT...I AM NOT TOO
ENTHRALLED WITH THE MODEL SOLUTIONS...AND WE MAY SEE THE CYCLONE
TURN OUT TO BE MORE OF A WEST-RUNNER THAN A RECURVER THROUGH THE
STRONG SUBTROPICAL RIDGE LOCATED TO THE NORTH.

[curtadams]

These discussions are based on there being a substative system to recurve. The system is facing a challenge: significant shear coming from the dry side. GFS predicts fairly strong shear over the area the storm is likely to occupy (possibly due to the system itself, though). You can see the shear on the 330Z Navy pic, with convection in the ITCZ starting to blow off to the W. That's often a lethal combination for a cyclone, especially a depression.