Broad area of low pressure to form over the eastern tropical Atlantic (Is Invest 91L)

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Broad area of low pressure to form over the eastern tropical Atlantic (Is Invest 91L)

#1 Postby CyclonicFury » Sun Sep 26, 2021 12:35 am

A broad area of low pressure could form over the eastern or central
tropical Atlantic early this week, to the west of the tropical wave
that will be moving off the coast of Africa. Thereafter,
environmental conditions could support some development of this
disturbance while it moves westward at 5 to 10 mph through the
middle of the week.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...low...30 percent.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#2 Postby Teban54 » Sun Sep 26, 2021 12:45 am

GFS is the main (and maybe the only) model that develops both this and the 0/60 wave, though it has been inconsistent: on some runs this system is favored, while on other runs the wave behind is favored.

Until the 18z run, it had both systems recurve OTS. But on the most recent 0z run, this 0/30 system doesn't recurve and heads west as a remnant low, and its vorticity contributes to the WCar system.

My hope is that only one of them develops, so we have a better chance of retiring another W name.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#3 Postby Category5Kaiju » Sun Sep 26, 2021 7:18 am

Teban54 wrote:GFS is the main (and maybe the only) model that develops both this and the 0/60 wave, though it has been inconsistent: on some runs this system is favored, while on other runs the wave behind is favored.

Until the 18z run, it had both systems recurve OTS. But on the most recent 0z run, this 0/30 system doesn't recurve and heads west as a remnant low, and its vorticity contributes to the WCar system.

My hope is that only one of them develops, so we have a better chance of retiring another W name.


Imho, whether the WCAR system becomes a powerhouse Wanda or Adria would be cool either way imho. The former as eerily remniscent of the other nasty "W" storm we had, and the latter the first name ever used from the new aux list. Of course I do not want to see death and chaos, but gotta admit, naming and retirement and that jazz is a part of what makes tracking hurricanes fun.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#4 Postby AlphaToOmega » Sun Sep 26, 2021 10:07 am

I cannot tell if this is of tropical or non-tropical origin.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#5 Postby cycloneye » Sun Sep 26, 2021 1:12 pm

Up to 50%.

A broad area of low pressure is expected to form over the eastern or
central tropical Atlantic early this week, to the west of the
tropical wave that will be moving off the coast of Africa.
Thereafter, environmental conditions are forecast to support some
development of this disturbance, and a tropical depression could
form by late this week while it moves westward at 5 to 10 mph.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...medium...50 percent.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#6 Postby underthwx » Sun Sep 26, 2021 1:53 pm

Teban54 wrote:GFS is the main (and maybe the only) model that develops both this and the 0/60 wave, though it has been inconsistent: on some runs this system is favored, while on other runs the wave behind is favored.

Until the 18z run, it had both systems recurve OTS. But on the most recent 0z run, this 0/30 system doesn't recurve and heads west as a remnant low, and its vorticity contributes to the WCar system.

My hope is that only one of them develops, so we have a better chance of retiring another W name.


With the proximity to Sam of this suspect area....will that limit or slow any development?....
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#7 Postby Teban54 » Sun Sep 26, 2021 2:12 pm

underthwx wrote:
Teban54 wrote:GFS is the main (and maybe the only) model that develops both this and the 0/60 wave, though it has been inconsistent: on some runs this system is favored, while on other runs the wave behind is favored.

Until the 18z run, it had both systems recurve OTS. But on the most recent 0z run, this 0/30 system doesn't recurve and heads west as a remnant low, and its vorticity contributes to the WCar system.

My hope is that only one of them develops, so we have a better chance of retiring another W name.


With the proximity to Sam of this suspect area....will that limit or slow any development?....

Seems like GFS as well as the 12z Euro/CMC (first time showing the system) only have it forming after Sam lifts out of the deep tropics past 20N.

Regardless, it can still form if it finds a perfect spot to avoid Sam's outflow. Jose 2017 formed and intensified to a high-end Cat 4 all while it was located to the ESE of Cat 5 Irma. It also helps that Sam's small size will likely limit its outflow somewhat, as compared to Irma.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#8 Postby underthwx » Sun Sep 26, 2021 2:14 pm

Teban54 wrote:
underthwx wrote:
Teban54 wrote:GFS is the main (and maybe the only) model that develops both this and the 0/60 wave, though it has been inconsistent: on some runs this system is favored, while on other runs the wave behind is favored.

Until the 18z run, it had both systems recurve OTS. But on the most recent 0z run, this 0/30 system doesn't recurve and heads west as a remnant low, and its vorticity contributes to the WCar system.

My hope is that only one of them develops, so we have a better chance of retiring another W name.


With the proximity to Sam of this suspect area....will that limit or slow any development?....

Seems like GFS as well as the 12z Euro/CMC (first time showing the system) only have it forming after Sam lifts out of the deep tropics past 20N.

Regardless, it can still form if it finds a perfect spot to avoid Sam's outflow. Jose 2017 formed and intensified to a high-end Cat 4 all while it was located to the ESE of Cat 5 Irma. It also helps that Sam's small size will likely limit its outflow somewhat, as compared to Irma.


I appreciate your informative reply Teban....that's interesting to me... thankyou...
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#9 Postby cycloneye » Sun Sep 26, 2021 6:43 pm

A broad area of low pressure appears to be be forming several
hundred miles southwest of the Cabo Verde Islands. Environmental
conditions are forecast to support further development of this
disturbance, and a tropical depression is likely to form around
midweek while it moves westward at 5 to 10 mph.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...high...70 percent.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#10 Postby SconnieCane » Sun Sep 26, 2021 7:22 pm

I see little speculation on future track for this as of yet...but orientation of the NHC "cherry zone" implies a deep low-rider that could pass 50W with no sign of following in Sam's wake... :eek:
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#11 Postby Stormybajan » Sun Sep 26, 2021 7:31 pm

Well with Sam taking all the attention, does anyone have a general consensus of where this wave is heading, how strong it might get and what to expect in the islands? Seems like most models develop this to a weak storm or TD then as it nears the islands completely falls apart. Shouldn't the presence of Sam significantly weaken the high pressure system and send this wave north?
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#12 Postby Category5Kaiju » Sun Sep 26, 2021 8:10 pm

Stormybajan wrote:Well with Sam taking all the attention, does anyone have a general consensus of where this wave is heading, how strong it might get and what to expect in the islands? Seems like most models develop this to a weak storm or TD then as it nears the islands completely falls apart. Shouldn't the presence of Sam significantly weaken the high pressure system and send this wave north?


Not if it remains weak; typically it's the stronger systems that can feel weaknesses. In that regard, I honestly would not be shocked to see this system remain at a low latitude and enter the Caribbean Sea while going westward
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#13 Postby Teban54 » Sun Sep 26, 2021 9:45 pm

Another AOI that popped out of nowhere. Nobody even bothered to make a thread until less than 24 hours ago.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#14 Postby Teban54 » Sun Sep 26, 2021 11:16 pm

Now that Sam watching is temporarily over, I have a bit more time to look at model runs.

As mentioned earlier, 12z (Sep 26) Euro and CMC now briefly develop both this system and the wave behind it. GFS also shows the same every run.
Models generally agree on a westward track, meaning the GFS no longer shows a recurve in the open Atlantic. There is disagreement on where exactly it will enter the Caribbean: 12z CMC and 12z GFS are the northernmost outliers with its remnant low reaching the northern tip of Lesser Antilles, while 12z Euro is the southernmost outlier and has its vorticity almost crashing into South America. The other GFS runs are somewhere inbetween.

Most models keep this system rather weak, peaking in the high 990s or higher and generally dissipating by the time it reaches the islands. Whether it's shear, dry air or Sam's cold wake, I don't know. Even models that have it enter the Caribbean don't show much redevelopment with the wave itself (the potential WCar system on GFS seems to be mostly related to a CAG or other kind of homegrown).
Given climatography, I wouldn't be surprised if this exceeds expectations and become stronger than currently forecast, though. It's October in the Caribbean, after all.

Update: 0z GFS continues to show its remnants tracking into the Caribbean with no development. 0z CMC has a Fujiwhara between the two systems and this one gets killed by the next wave's outflow while moving north, which I don't think is likely.
Last edited by Teban54 on Mon Sep 27, 2021 1:30 am, edited 1 time in total.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#15 Postby Extratropical94 » Mon Sep 27, 2021 1:03 am

Disorganized showers and thunderstorms are associated with a broad
area of low pressure located several hundred miles southwest of the
Cabo Verde Islands. Environmental conditions are forecast to be
conducive for further development of this disturbance, and a
tropical depression is likely to form around midweek while it moves
westward to west-northwestward at 5 to 10 mph over the central
tropical Atlantic.
* Formation chance through 48 hours...low...30 percent.
* Formation chance through 5 days...high...80 percent.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#16 Postby NDG » Mon Sep 27, 2021 6:04 am

Chances for development do indeed look fairly high but it will have a tough battle to fight with the forecasted shear over the central Atlantic from a strong ULL coming down behind Sam.
If it can survive and make it into the Caribbean next week it will have to be watched as UL conditions improve there next week.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#17 Postby abajan » Mon Sep 27, 2021 8:23 am

This is now Invest 90L.
My apologies, wrong system.
Last edited by abajan on Mon Sep 27, 2021 8:28 am, edited 1 time in total.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#18 Postby Extratropical94 » Mon Sep 27, 2021 8:25 am

abajan wrote:This is now Invest 90L.


I believe the wave emerging off the coast of Africa is 90L. This AOI has not been tagged yet.
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#19 Postby abajan » Mon Sep 27, 2021 8:27 am

Extratropical94 wrote:
abajan wrote:This is now Invest 90L.


I believe the wave emerging off the coast of Africa is 90L. This AOI has not been tagged yet.

Oops! My bad. :oops:
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Re: Broad area of low pressure to form over the eastern tropical Atlantic

#20 Postby cycloneye » Mon Sep 27, 2021 8:40 am

Stay tuned. Invest comming soon.
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