ATL: ARTHUR - Post-Tropical

[northjaxpro]

Here are my two cents. The reason why 90L is hanging around the straits for longer than expected is because the nontropical feature at the mid and upper levels which was the catalyst for it's initial development has sheared out and ejected to the NE. Leaving a very shallow yet warm core low at the surface. Since its so shallow, it is feeling the low level easterly flow. Once the shortwave propagates east and initiates convection and associated pressure falls, it'll start moving NE in accordance to the mid level flow.

Very astute observation TyphoonTy!

[Aric Dunn]

Just posted a version of the HRR model (15z HRWN) in the model thread.

looks like it could be a distinct possibility.

viewtopic.php?f=59&t=120862&p=2801196#p2801196

[chaser1]

Judging by the clouds over Cuba, south of the swirl, there may be a sudden shift to more west winds.

yeah current surface obs from Havana, Matanzas and offhsor Bouy/ships show a closed wind field with a central low pressure with that naked vort.

Matanzas should switch to west as that vort moves closer.

with convection waning associated with the vort to the NE and some increasing moisture coming in at the mid levels .. should see convection fire off between Cuba and keys over the next several hours.

unless we get a redevelopment of the center east of key largo.

Aric, how many times have we seen this? I think that a redevelopment east of Key Largo is quite plausible. Could be a boat-load of additional precip to line up and train into Dade & Broward late this afternoon and into this evening. If that were to occur Gator & SoFla could well see 24 hr. rainfall upwards of 5"-6" or more. While overall net motion appears to be "nill", continued slow reorganization and propagation will likely result in better consolidating somewhere between the N.W. Bahamas & S.E. Florida coast on Sunday. I could see the NHC hoisting T.S. Watches (PTS Advisories) by tonight/tomm. a.m. for N. Broward & Palm Beach coastline for the Saturday night-Sunday period.

Edit: As soon as I posted this, I saw your posted HRR. Certainly would carry some nice squalls further up the coast if that occured!

[Miami Storm Tracker]

I had mention this last evening based on what I was seeing on radar. With the current COC reforming of the coast of Key Largo Florida City. It looks at least for now that is still a possibility.

[Aric Dunn]

Judging by the clouds over Cuba, south of the swirl, there may be a sudden shift to more west winds.

yeah current surface obs from Havana, Matanzas and offhsor Bouy/ships show a closed wind field with a central low pressure with that naked vort.

Matanzas should switch to west as that vort moves closer.

with convection waning associated with the vort to the NE and some increasing moisture coming in at the mid levels .. should see convection fire off between Cuba and keys over the next several hours.

unless we get a redevelopment of the center east of key largo.

Aric, how many times have we seen this? I think that a redevelopment east of Key Largo is quite plausible. Could be a boat-load of additional precip to line up and train into Dade & Broward late this afternoon and into this evening. If that were to occur Gator & SoFla could well see 24 hr. rainfall upwards of 5"-6" or more. While overall net motion appears to be "nill", continued slow reorganization and propagation will likely result in better consolidating somewhere between the N.W. Bahamas & S.E. Florida coast on Sunday. I could see the NHC hoisting T.S. Watches (PTS Advisories) by tonight/tomm. a.m. for N. Broward & Palm Beach coastline for the Saturday night-Sunday period.

Edit: As soon as I posted this, I saw your posted HRR. Certainly would carry some nice squalls further up the coast if that occured!

yeah that model run lines up quite well with what is going on right now. the fading vort down by cuba sifting nne convection building west over the central keys. all point to a momentum shift.

could easily slide right along the coast of Se florida over the next 12 hours.

[Aric Dunn]

Red circle is where the momentum is transferring too convergence is increasing

yellow circle is the old vort ... the blue inflow line coming from the south were all focused into that convection earlier .. but since that has died .. the overall broad wind field and become less elongated..

watch for a better llc to potentially develop or show signs in that red circle area..

[cycloneye]

 https://twitter.com/TropicalTidbits/status/1261321094193176579

[Aric Dunn]

Developing circ currently in red.

the area in yellow is about to pop. Pressures are dropping.. old vort is dead now. westerly cloud lines filling in around the area circled in red.

convergence can be seen on 1km visible. low level cloud deck is thickening..

[CourierPR]

Aric, your position is quite divergent from Levi Cowan's. Would you please explain?

[Aric Dunn]

Aric, your position is quite divergent from Levi Cowan's. Would you please explain?

What is divergent? he calls out for a generalized area.

I am being very specific to current dynamics. He expects it will reform to the NNE later on.

I am watching the beginnings of a mesoscale feature that may deepen in the next few hours as convection builds in an area of increasing convergence.

[GCANE]

IMHO, there is too much dry air, in a good portion of the troposphere, inside the trough.
Would need to get that moistened up before anything can kick off.
Shortwave is coming in with some moisture, but will take time.
Could also see popups over Cuba which would entrain moisture later tonight.
Also 355K PV is putting a lid on any type of vertical vort expansion.

[GCANE]

Seeing two eddies on the western side of the trof axis.
Cumulus is building on the one which is more west and closer to the shortwave.
A sign that the atmosphere is beginning to moisten slowly.

[Aric Dunn]

Seeing two eddies on the western side of the trof axis.
Cumulus is building on the one which is more west and closer to the shortwave.
A sign that the atmosphere is beginning to moisten slowly.

That developing circ I identified earlier is becoming more defined. The column does appear to be saturating more as you mentioned. low levels thickening.

old vort to south is completely gone and westerly cloud lines forming around the new soon to be llc.

it should get pulled to the nne towards the developing convection over the next few hours.

[Jr0d]

The future strength is dependent on very slight track shifts. It it wobbles a little west the circulation will be over land and may not become a storm. If it stays east and rides the gulf stream we may see a much stronger storm than originally expected.

It looks like tomorrow, everything will start to come together for significant strengthening if it stays over water.

[GCANE]

Seeing two eddies on the western side of the trof axis.
Cumulus is building on the one which is more west and closer to the shortwave.
A sign that the atmosphere is beginning to moisten slowly.

That developing circ I identified earlier is becoming more defined. The column does appear to be saturating more as you mentioned. low levels thickening.

old vort to south is completely gone and westerly cloud lines forming around the new soon to be llc.

it should get pulled to the nne towards the developing convection over the next few hours.


https://i.ibb.co/Q6DG2Zv/Capture.png

More west winds cutting into the axis.
It's definitely tightening up.

[Aric Dunn]

Seeing two eddies on the western side of the trof axis.
Cumulus is building on the one which is more west and closer to the shortwave.
A sign that the atmosphere is beginning to moisten slowly.

That developing circ I identified earlier is becoming more defined. The column does appear to be saturating more as you mentioned. low levels thickening.

old vort to south is completely gone and westerly cloud lines forming around the new soon to be llc.

it should get pulled to the nne towards the developing convection over the next few hours.


https://i.ibb.co/Q6DG2Zv/Capture.png

More west winds cutting into the axis.
It's definitely tightening up.

yep.. the area I like to call the void.. is being filled.

It is the lengthening curved cloud line on the SE side that is a dead giveaway.

[northjaxpro]

The future strength is dependent on very slight track shifts. It it wobbles a little west the circulation will be over land and may not become a storm. If it stays east and rides the gulf stream we may see a much stronger storm than originally expected.

It looks like tomorrow, everything will start to come together for significant strengthening if it stays over water.

I think it will likely traverse north/northeast right up along the Gulf Stream, just off the Southeast U.S. Atlantic Coast. Arthur imo will become a rather strong early season cyclone, and it would not surprise me to see it possibly become a Cat 1 hurricane early next week, if it can fully maximize the influence of the Gulf Stream Current.

Also, the 12Z GFS tracks future Arthur a bit closer to the NC Outer Banks by Tuesday, compared to previous runs.

[SFLcane]

Judging by the clouds over Cuba, south of the swirl, there may be a sudden shift to more west winds.

yeah current surface obs from Havana, Matanzas and offhsor Bouy/ships show a closed wind field with a central low pressure with that naked vort.

Matanzas should switch to west as that vort moves closer.

with convection waning associated with the vort to the NE and some increasing moisture coming in at the mid levels .. should see convection fire off between Cuba and keys over the next several hours.

unless we get a redevelopment of the center east of key largo.

Aric, how many times have we seen this? I think that a redevelopment east of Key Largo is quite plausible. Could be a boat-load of additional precip to line up and train into Dade & Broward late this afternoon and into this evening. If that were to occur Gator & SoFla could well see 24 hr. rainfall upwards of 5"-6" or more. While overall net motion appears to be "nill", continued slow reorganization and propagation will likely result in better consolidating somewhere between the N.W. Bahamas & S.E. Florida coast on Sunday. I could see the NHC hoisting T.S. Watches (PTS Advisories) by tonight/tomm. a.m. for N. Broward & Palm Beach coastline for the Saturday night-Sunday period.

Edit: As soon as I posted this, I saw your posted HRR. Certainly would carry some nice squalls further up the coast if that occured!

90L has over performed in terms of rainfall with 3-6 inches in some SFL locations. But wind has been a non issue almost dead calm. I have yet to see your bonified squall from this system. Actually seeing some sun breaks now

[cycloneye]

18az Best Track. Aric,is that the location you are looking at?

Location: 24.2°N 80.7°W
Maximum Winds: 25 kt Gusts: nan kt
Minimum Central Pressure: 1011 mb
Environmental Pressure: 1013 mb
Radius of Circulation: 120 NM
Radius of Maximum Wind: 90 NM

[Aric Dunn]

18az Best Track. Aric,is that the location you are looking at?

Location: 24.2°N 80.7°W
Maximum Winds: 25 kt Gusts: nan kt
Minimum Central Pressure: 1011 mb
Environmental Pressure: 1013 mb
Radius of Circulation: 120 NM
Radius of Maximum Wind: 90 NM

https://i.imgur.com/RB3Po6G.png

yes it is.. dead on..