ATL: DORIAN - Post-Tropical - Discussion

[TropicalAnalystwx13]

What will be working against the system later in the week, and is it less favorable than Chantal had?

Depends on how it tracks. If it follows the southern end of the model guidance, just a brief dip into sub-26C waters. If it follows the northern end, a prolonged track across waters too cool for intensification, a more stable environment, faster trade winds, and eventually wind shear.

[NDG]

I don't get where there'll be any problem with SSTs. Given the rough track this is going on, and consensus is pretty tightly clustered, this will never go over water lower than 27C. I drew in the roughly expected path for the next few days over an RGB sat image with current SSTs.

Your track is a bit too far south.
It will be tracking over some sub 26 deg C water after 24-36 hrs, if the GFS is correct.

[ozonepete]

Even on the track you posted it would spend a day at most over marginal SSTs (darker green). The lighter green area, if that panned out, is more than enough for a TS to maintain. It just doesn't seem to be a significant factor.

[cycloneye]

It may be moving a little bit south of due west at this time. Will be interesting to see if that is a temporary jog or more than that.

[Alyono]

They are the experts that know all of what is going on with the system with the many tools they have and decided that it didn't warranted more than 30% at this time.

Each forecaster has a different opinion as to whether or not this will develop. I usually am not surprised who at NHC makes the forecast, just based upon the probabilities given

As for the percentage, I for one think that the best chance to develop may not occur until about 5-7 days, once it moves past the shear. I am only giving this a 20 percent chance of development through 48 hours

[RL3AO]

Lots of strong westerly winds north of the low likely shearing it. Also note a TUTT forming south of Bermuda which won't make life easy later on.

[NDG]

:uarrow: Even on the track you posted it would spend a day at most over marginal SSTs (darker green). The lighter green area, if that panned out, is more than enough for a TS to maintain. It just doesn't seem to be a significant factor.

Very true, I have seen tropical systems survive 25 deg C waters but as we know a bigger obstacle could be the more stable air further away from the itcz.

[ozonepete]

:uarrow: Even on the track you posted it would spend a day at most over marginal SSTs (darker green). The lighter green area, if that panned out, is more than enough for a TS to maintain. It just doesn't seem to be a significant factor.

Very true, I have seen tropical systems survive 25 deg C waters but as we know a bigger obstacle could be the more stable air further away from the itcz.

Yeah, mainly the dreaded dust. Right now you can see the SAL dust cluster is west and north of it but moving ahead of it at the same forward speed as this disturbance. If this system maintains its current speed or slows down at all it may never ingest much of it, similar to what happened with Chantal. Mid-level moisture is good right now (pretty obvious with all of that convection) but that can change as well. I would really want to wait for tonight's 00Z runs but especially tomorrow morning's runs to see what the models do with it (and its future environment) after they initialize it better.

[SFLcane]

Plenty of trofs in line ready to weaken what ever ridge there is of the southeast.

[meriland23]

I know how reliable GFS/EURO is with the general track and intensity of disturbances, but how reliable are they at forecasting dry air/ shear/ etc this far out?

[ozonepete]

I know how reliable GFS/EURO is with the general track and intensity of disturbances, but how reliable are they at forecasting dry air/ shear/ etc this far out?

They're pretty good with dry air but the models often get shear really wrong more than a day or two out. There's just not enough upper air observations out over the Atlantic so the models don't have good input to make a better forecast. I always look to see how shear will be even 1-5 days out but I just don't trust it very much past the second day. It's often way over-estimated or under-estimated.

[RL3AO]

When you look at TPW loop, I notice two things.

1) Its got a very noticeable spin, especially for a system that has just left Africa.
2) The dry air seems to be moving faster, or at least the same speed as the wave.

http://tropic.ssec.wisc.edu/real-time/m ... /main.html

[NDG]

I know how reliable GFS/EURO is with the general track and intensity of disturbances, but how reliable are they at forecasting dry air/ shear/ etc this far out?

IMO, they handle moisture content better in the atmosphere but shear is not handled very well. I lately like to stay in the 48-72 hr range when it comes to shear.

[floridasun78]

that look like nhc think going out to sea

[meriland23]

When you look at TPW loop, I notice two things.

1) Its got a very noticeable spin, especially for a system that has just left Africa.
2) The dry air seems to be moving faster, or at least the same speed as the wave.

http://tropic.ssec.wisc.edu/real-time/m ... /main.html

I know, it is like Africa gave birth to a tropical storm almost, not a wave.. it is just kicking it up a few notches quite rapidly..

[meriland23]

I know how reliable GFS/EURO is with the general track and intensity of disturbances, but how reliable are they at forecasting dry air/ shear/ etc this far out?

IMO, they handle moisture content better in the atmosphere but shear is not handled very well. I lately like to stay in the 48-72 hr range when it comes to shear.

So what is working against this storm in the long run? And are these pretty definite circumstances ?

[RL3AO]

Wind shear, unless I'm totally misreading the models.

[Alyono]

When you look at TPW loop, I notice two things.

1) Its got a very noticeable spin, especially for a system that has just left Africa.
2) The dry air seems to be moving faster, or at least the same speed as the wave.

http://tropic.ssec.wisc.edu/real-time/m ... /main.html

watch for dry air from BEHIND the system. The air ahead is seldom the dry air that impacts a system in the tropical Atlantic

[Blown Away]

00z models...TVCN goes WNW and ends just NE of Caribbean...Hard to go against the models saying limited development at best

[Alyono]

I know how reliable GFS/EURO is with the general track and intensity of disturbances, but how reliable are they at forecasting dry air/ shear/ etc this far out?

IMO, they handle moisture content better in the atmosphere but shear is not handled very well. I lately like to stay in the 48-72 hr range when it comes to shear.

models are notoriously HORRIBLE for predicting dry air in the tropics. Have not looked in recent years, but before, RH values tended to have a high bias