ATL: KAREN - Remnants - Discussion

[storm_in_a_teacup]

The GFS depicts low shear and does little with it so that in itself makes no sense. And this may be another for the Bahamas which in no way if fair as they’ve been hit 2x in 2 weeks and maybe Florida needs to watch in case of a similar solution to the HWRF intensity wise with the GFS track. The HWRF intensity wise stood head and shoulders above the rest with Dorian so it can’t be discounted

From what I saw on visible satellite on Saturday, up until now, I don't think the issue was shear, but the presence of dry air aloft. The tell-tale sign to me was those arcus clouds that raced WNW-NW away from the area of convection on the east side of the wave axis. You don't get large surface outflow boundaries accelerating outward like that in the deep tropics unless you have some mid level dry air. That having been said, to the west, the 00Z RAOBs from Port-of-Spain and Point-a-Pitre were quite moist, and really didn't show much dry air aloft at all. So if dry air aloft had been a problem, it won't be for much longer.

How exactly does the mid level dry air lead to the formation of the arcus clouds? (apologies for my ignorance)

[cycloneye]

Satellite, radar and surface data indicate that the area of low
pressure located just north of Tobago in the Windward Islands is
becoming better organized and is producing winds to near tropical
storm force in the eastern portion of the system. Further
development of this disturbance is expected over the next couple of
days, and a tropical depression or tropical storm will likely form
while it moves west-northwestward and then northwestward at 10 to 15
mph across the Windward Islands and over the eastern Caribbean Sea.
The system is then expected to turn northward, moving near Puerto
Rico and the Virgin Islands on Tuesday. Heavy rainfall and strong
gusty winds are likely over much of the Leeward and Windward Islands
during the next couple of days and will spread across Puerto Rico
and the Virgin Islands by Monday night or Tuesday. Interests across
the eastern Caribbean should monitor the progress of this low, and
tropical storm watches and warnings will likely be required for
portions of the Leeward Islands and Puerto Rico later today. An Air
Force Hurricane Hunter is scheduled to investigate the system this
afternoon.
* Formation chance through 48 hours...high...80 percent.
* Formation chance through 5 days...high...80 percent.

[AJC3]

The GFS depicts low shear and does little with it so that in itself makes no sense. And this may be another for the Bahamas which in no way if fair as they’ve been hit 2x in 2 weeks and maybe Florida needs to watch in case of a similar solution to the HWRF intensity wise with the GFS track. The HWRF intensity wise stood head and shoulders above the rest with Dorian so it can’t be discounted

From what I saw on visible satellite on Saturday, up until now, I don't think the issue was shear, but the presence of dry air aloft. The tell-tale sign to me was those arcus clouds that raced WNW-NW away from the area of convection on the east side of the wave axis. You don't get large surface outflow boundaries accelerating outward like that in the deep tropics unless you have some mid level dry air. That having been said, to the west, the 00Z RAOBs from Port-of-Spain and Point-a-Pitre were quite moist, and really didn't show much dry air aloft at all. So if dry air aloft had been a problem, it won't be for much longer.

How exactly does the mid level dry air lead to the formation of the arcus clouds? (apologies for my ignorance)

Arcus clouds form along the leading edge of most thunderstorm outflows. In Florida, we commonly see them in the form of of smaller scale shelf clouds. Larger scale arcus clouds form through the acceleration of thunderstorm downdrafts. Air tends to warm and dry out as it descends - an extreme example of this is an orographically (terrain-) forced wind such as a chinook. If the air aloft is already dry to begin with, this only enhances the acceleration and transport of that drier air downward. The resultant arcus clouds act as a detriment to the convective structure of a developing TC, as these winds tend to blow in a straight line away from the center.

[AJC3]

The GFS depicts low shear and does little with it so that in itself makes no sense. And this may be another for the Bahamas which in no way if fair as they’ve been hit 2x in 2 weeks and maybe Florida needs to watch in case of a similar solution to the HWRF intensity wise with the GFS track. The HWRF intensity wise stood head and shoulders above the rest with Dorian so it can’t be discounted

From what I saw on visible satellite on Saturday, up until now, I don't think the issue was shear, but the presence of dry air aloft. The tell-tale sign to me was those arcus clouds that raced WNW-NW away from the area of convection on the east side of the wave axis. You don't get large surface outflow boundaries accelerating outward like that in the deep tropics unless you have some mid level dry air. That having been said, to the west, the 00Z RAOBs from Port-of-Spain and Point-a-Pitre were quite moist, and really didn't show much dry air aloft at all. So if dry air aloft had been a problem, it won't be for much longer.

Come to think of it, this reminds me of the post I made several days ago regarding this wave being overtken by an SAL surge...

...Unless this stays right on the western or southern periphery of that air mass, I'm thinking this wave may struggle to maintain convection. It'll be interesting to see...

Indeed, it's been lying along the SW flank of the large SAL seen here...



In the 3.9UM shortwave IR channel this morning, you can still see the remnant of that arcus cloud well to the N-NE of 99L, and its pretty apparent just how convectively suppressed it is within that air mass, given the dearth of cumulus cloud elements there...



So perhaps I was a bit premature in my earlier speculation about it not having to contend with dry air for much longer - we'll have to see how that SAL to the north evolves over the next few days as it spreads westward.

[NotSparta]

From what I saw on visible satellite on Saturday, up until now, I don't think the issue was shear, but the presence of dry air aloft. The tell-tale sign to me was those arcus clouds that raced WNW-NW away from the area of convection on the east side of the wave axis. You don't get large surface outflow boundaries accelerating outward like that in the deep tropics unless you have some mid level dry air. That having been said, to the west, the 00Z RAOBs from Port-of-Spain and Point-a-Pitre were quite moist, and really didn't show much dry air aloft at all. So if dry air aloft had been a problem, it won't be for much longer.

How exactly does the mid level dry air lead to the formation of the arcus clouds? (apologies for my ignorance)

Arcus clouds form along the leading edge of most thunderstorm outflows. In Florida, we commonly see them in the form of of smaller scale shelf clouds. Larger scale arcus clouds form through the acceleration of thunderstorm downdrafts. Air tends to warm and dry out as it descends - an extreme example of this is an orographically (terrain-) forced wind such as a chinook. If the air aloft is already dry to begin with, this only enhances the acceleration and transport of that drier air downward. The resultant arcus clouds act as a detriment to the convective structure of a developing TC, as these winds tend to blow in a straight line away from the center.

Also, the air rushing outward encourages llvl divergence and anticyclonic flow at the sfc, which weakens the cyclonic flow.

[AJC3]

How exactly does the mid level dry air lead to the formation of the arcus clouds? (apologies for my ignorance)

Arcus clouds form along the leading edge of most thunderstorm outflows. In Florida, we commonly see them in the form of of smaller scale shelf clouds. Larger scale arcus clouds form through the acceleration of thunderstorm downdrafts. Air tends to warm and dry out as it descends - an extreme example of this is an orographically (terrain-) forced wind such as a chinook. If the air aloft is already dry to begin with, this only enhances the acceleration and transport of that drier air downward. The resultant arcus clouds act as a detriment to the convective structure of a developing TC, as these winds tend to blow in a straight line away from the center.

Also, the air rushing outward encourages llvl divergence and anticyclonic flow at the sfc, which weakens the cyclonic flow.

You know, I had it in my mind to mention that it was "detrimental to vortical and convective structure, but the thought never made it from my head to my fingers. LOL

Great point, which my 55 year old noggen almost mentioned.

[AJC3]

Well, after seeing the 00Z op-GFS trend north and the op-Euro trend west, my first thoughts on what to look for through the first half of next are as follows:

1) Where and how fast 99L congeals a low level vortex. Based on the eastern Caribbean radar mosaic, there are hints at this having already occurred along the wave axis near 12N 59.5W, give or take.

2) How fast the system moves through the E and NE Caribbean and whether the system moves straight north or a little east of due north through days 5-6. The new 00Z op-GFS is nearly 4 degrees east of the ECM before it gets trapped and sent westward. Hence it winds up farther north.

3) The strength and orientation of the eastern CONUS-western ATLC ridge, particularly on its eastern flank. We'll also have to watch the amplification of a large central Atlantic trough, which up until Saturday, had been forecast to erode this eastern flank to the point that the system stalled and then was still able to escape to the north.

This is still a LONG ways off, and the global model guidance will surely shift around quite a bit more in their respective solutions. As always..."trends and ensembles" will be the way to go here...

[LarryWx]

If something like the 0Z Euro were to verify, it would be the 4th season in a row with a H threat to the SE US in early Oct! Is Oct the new Sep? Let's hope the 0Z Euro is drunk! The scary thing is that it may not be.

[sma10]

Aric. Paging Aric. Lmao

[christchurchguy]

Seems to be developing more banding this morning.
https://imgur.com/a/DKz8Z9C

[Jr0d]

Seems to be developing more banding this morning.

I'm thinking they will start issuing PTC advisories today, especially since the winds are likely tropical storm force.

[TheStormExpert]

We have Karen!

[northjaxpro]

Well now, it sure looks like we are all going to be doing some potential long nights burning the midnight oil with this potential over the course of the next 7-10 days.

This is shaping up to be quite the memorable tropical season and we look to close out September with the potential bang of seeing two more named storms for the month.

Slow season folks? There were even a few folks on the forum earlier in July through up into mid-August with the ridiculous season cancel posts. Huh?? I think not!! Mother Nature turned the ignition switch on in the tropics since mid-August and has never looked back!

We still have October to come. I think we will see several more named storms in the upcoming month. 2019 North Atlantic season has quickly become one of its most destructive and deadliest on record and may end up as the single deadliest with Dorian's catastrosphe on The Bahamas alone!

What a turn of events of this season. This just goes to show everyone NEVER, EVER underestimate the tropics, no matter the circimstances!!!

[jlauderdal]

Well now, it sure looks like we are all going to be doing some potential long nights burning the midnight oil with this potential over the course of the next 7-10 days.

This is shaping up to be quite the memorable tropical season and we look to close out September with the potential bang of seeing two more named storms for the month.

Slow season folks? There were even a few folks on the forum earlier in July through up into mid-August with the ridiculous season cancel posts. Huh?? I think not!! Mother Nature turned the ignition switch on in the tropics since mid-August and has never looked back!

We still have October to come. I think we will see several more named storms in the upcoming month. 2019 North Atlantic season has quickly become one of its most destructive and deadliest on record and may end up as the single deadliest with Dorian's catastrosphy on The Bahamas alone!

What a turn of events of this season. This just goes to show everyone NEVER, EVERunderestimate the tropics, no matter the circimstances!!!

every season we get the mid summer season cancel posts

the models have been trying desperately for weeks to get something into florida and have failed so far, btw

the sw carib in early October is starting to look interesting...my 50 gallons of gas and 30 gallons of water from Dorian preps remain on standby...i did have to take the shutters down, guy across the street never took his down

[abajan]

The wind at my location were definitely stronger when I awoke this morning (around 4:40). And I'm sure we got gusts in excess of 50 mph during the last half-hour or so. Thankfully, they have died down now.

[Weatherwatcher2018]

Why isn't the island of Barbados on warning

[northjaxpro]

I understand that more than anyone else Jlauderdal, which makes my point!! I just wish people would cease with the season cancel posts. They do not serve any purpose whatsoever!

Meanwhile we are going to be dealing with Karen for quite a while it appears with the loop back. These type of systems drive me crazy. Elena in 1985 does it for me. Jeanne was quite memorable in 2004 as well.
..

[abajan]

Well now, it sure looks like we are all going to be doing some potential long nights burning the midnight oil with this potential over the course of the next 7-10 days.

This is shaping up to be quite the memorable tropical season and we look to close out September with the potential bang of seeing two more named storms for the month.

Slow season folks? There were even a few folks on the forum earlier in July through up into mid-August with the ridiculous season cancel posts. Huh?? I think not!! Mother Nature turned the ignition switch on in the tropics since mid-August and has never looked back!

We still have October to come. I think we will see several more named storms in the upcoming month. 2019 North Atlantic season has quickly become one of its most destructive and deadliest on record and may end up as the single deadliest with Dorian's catastrosphe on The Bahamas alone!

What a turn of events of this season. This just goes to show everyone NEVER, EVER underestimate the tropics, no matter the circimstances!!!

Agree with everything except the possibility of it ending up as the deadliest season. It will be hard to top the 1780 record.

[abajan]

Why isn't the island of Barbados on warning

I guess they figure a warning would be mostly after the fact and be too short-lived, as the winds should diminish here within the next few hours.

[Mialco]

Why isn't the island of Barbados on warning

I guess they figure a warning would be mostly after the fact and be too short-lived, as the winds should diminish here within the next few hours.

abajan - shouldn't we have at least had some sort of advisories? Not even flood watches/warnings have been isused (or did I miss them?)