ATL: DORIAN - Post-Tropical - Discussion

[cycloneye]

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Joe Bastardi ‏@BigJoeBastardi 14m

Tropical disturbance south of Cape Verdes probably a tropical storm already. Can it beat the dry air is next question

[Aric Dunn]

very good pass..

[TheStormExpert]

There's not nearly as much dry air as there was when Chantal was around, but there is enough to maybe cause some problems.

[floridasun78]

Up to 70%. That almost guarantees an upgrade during the next TWO. According to the statistics, 100% of past storms to receive a 70% or higher chance for development have developed.

i think their wait untill 6am not seen upgrade at 2am before unless near land

[TheStormExpert]

Looks as if it's trying to get it's act together rather quickly. Convection looks to be increasing too.

http://tropicaltidbits.com/satellite/images/eatl_ir.gif

[ozonepete]

Ok, I got one for you all, with 98L getting itself underneath a 600+dm ridge here in the next few days, why won't it be hauling its rear end to the west at like 30 mph? That is one powerful ridge and you would think the gradient would be such that the trades would be screaming. I suppose it is far enough north for this not to matter as much? That struck me as a possible reason why this would get killed off: moving too fast. But - perhaps not? What say you?

A very logical question. The surface winds at the outer edges under an anticyclone don't depend on the strength of the anti-cyclone (vertical pressure gradient). They depend on the interaction at the surface edges of the anti-cyclone with other surface features (horizontal pressure gradient). I would have to go back and look at Chantal's environment again to figure it out, but clearly there was a higher horizontal pressure gradient at the surface along 10-20 degrees when Chantal went through last week. I'll try to look at this further and let you know what the difference is now.

[TheStormExpert]

Latest Water Vapor shows that dry air should not be much of an issue in the short-term future. Also notice how the convection looks less promising on here than IR satellite.

[cycloneye]

Latest Water Vapor shows that dry air should not be much of an issue in the short-term future. Also notice how the convection looks less promising on here than IR satellite.

http://img11.imageshack.us/img11/3858/qet2.jpg

That image is the Eastern Atlantic 6 hour interval. The SSD floater is better as it updates every 15 minutes.Shortly,it will begin on that timeframe as it gets close to the 30W longitude.

[TheStormExpert]

So far the 0z GFS has Invest 98L a little further north than the 18z @ 96hr.

[beoumont]

a note about SST.

It is NOT SST itself that is the important factor. It is the difference between SST and upper trop temperature. If SST were all that mattered, then we wouldn't see late season genesis over sub 70F waters in the N Atl

The 80 degree "threshold" that is commonly referred to us layman as one of the necessary ingredients for tropical cyclone formation, as you note, "in itself" is not as "important" as that meteorological lapse rate you pointed out.

But, on this earth, above the tropical oceans during hurricane season months the upper tropospheric temperature does not vary but a few degrees; hence the threshold SST is almost always close to 80 degrees F (27 C) in the tropics.

I am not certain of this, as this conclusion comes only from observations, not studying theory; so please let me know if my above conclusion is not correct.

As you noted, those developments over cooler waters almost always occur at higher latitudes.

So, when tracking an easterly wave across the tropics, or a TC (tropical depression), it is almost always very important when that system goes from 26 degree C. waters into 27+ degree C. waters, or vise versa. (The convection increases in the former, decreases in the vice-versa).

Similarly, if one looks at the 500mb temperatures above a disturbance, it is almost always necessary, in the tropics, to see at least as warm as minus 5 degrees C. for development to occur. And when one sees minus 3 degrees C at 500 mb. development becomes very much more likely yet.
Those 2 little degrees can make a world of difference - from steady development to explosive.

[South Texas Storms]

I wonder if it will go out to sea this run? It's definitely more north than the 18z run.

[TheStormExpert]

I wonder if it will go out to sea this run? It's definitely more north than the 18z run.

I don't know that ridge looks like it's still really strong.
@111hr.

[SouthDadeFish]

Curved band developing to the NW of the center:

[Riptide]

Strong blocking ridge, heading WSW into the TC shredder at 150.

[TheStormExpert]

Definite no to the escape route I would assume as of 141hr.

[Aric Dunn]

Curved band developing to the NW of the center:

still being affected by easterly shear though

[TheStormExpert]

Strong blocking ridge, heading WSW into the TC shredder at 150.

Where are you getting this? Cause @ 156hr. GFS has it north of the gap between Hispaniola and Puerto Rico.

[cycloneye]

Just north of PR.

[Bartholemew Roberts]

Up to 70%. That almost guarantees an upgrade during the next TWO. According to the statistics, 100% of past storms to receive a 70% or higher chance for development have developed.

And here is in graphic.

[img ]http://icons.wxug.com/hurricane/2013/two_genesis_2012.png[/img]

DOes that mean there is a 100% chance of storm?

[TheStormExpert]

Opened back up into a TW @ 171hr. Model run trending north though. Maybe the start a new trend?