African Wave Leading Tails

[drezee]

 https://twitter.com/andretrotter/status/1281852337909379072

[cycloneye]

 https://twitter.com/JPKassell/status/1281968548689195008

[CFLHurricane]

This is certainly a stark contrast to leaner years like 2015 when we were swearing into late August that the wave train was leaving any day now.

[AutoPenalti]

The infamous battle between SAL and AEW’s.

[CyclonicFury]

The infamous battle between SAL and AEW’s.

The SAL usually wins...for now. Starting next month that won't always be the case.

[drezee]

The tail is still there...seems like there is no wave passing

[Aric Dunn]

The tail is still there...seems like there is no wave passing

The wave axis is just leaving the coast. pretty good large broad rotation with it. light sal north of it. Otherwise it is farther north than most of the waves recently. some convection east the cape verde islands.

It does resemble what would be a peak season wave. The type that turn north far east.

[drezee]

The tail is still there...seems like there is no wave passing

The wave axis is just leaving the coast. pretty good large broad rotation with it. light sal north of it. Otherwise it is farther north than most of the waves recently. some convection east the cape verde islands.

It does resemble what would be a peak season wave. The type that turn north far east.


https://i.ibb.co/Xj3fsjK/50186380.gif

I realized after I look at the surface obs. Geez, it is moving so slow. Dakar has pure South winds...that is rare in July!

https://weather.com/weather/tenday/l/Da ... 70d7560215

[Aric Dunn]

The tail is still there...seems like there is no wave passing

The wave axis is just leaving the coast. pretty good large broad rotation with it. light sal north of it. Otherwise it is farther north than most of the waves recently. some convection east the cape verde islands.

It does resemble what would be a peak season wave. The type that turn north far east.


https://i.ibb.co/Xj3fsjK/50186380.gif

I realized after I look at the surface obs. Geez, it is moving so slow. Dakar has pure South winds...that is rare in July!

https://weather.com/weather/tenday/l/Da ... 70d7560215

looks like this wave acutally cleared the path of SAL outbreaks. it brought rain to all the major SAL development regions.

[drezee]

I think the leading tail stays

[AJC3]

The current east Atlantic monsoon trough pattern (i.e. an active east Atlantic ITCZ) is not all that uncommon, although I should read up on it more to get a better handle on its intaseasonal variability and duration. For instance, how long does this pattern last compared to say a CAG pattern? How is it impacted (perhaps even inititated?) by WWBs via equatorial (trapped) CCKW waves, the MJO, etc. etc. As already alluded to, the pre-existing broad band of low level convergence/vorticity often interacts with AEWs departing the coast of Africa to induce "Cape Verde" tropical cyclogenesis, especially as we get into the teeth of the CV/MDR season. Pretty easy to visualize this.

Also wondering how best to handle this thread. We should probably limit discussion in this thread to the pattern itself, and keep the threads for individual waves that (may) interact with it separate. Finally, I'm not a big fan of the "Leading Tail" colloquialism in the thread title. I've never seen it used in any sort of discussion (let alone paper), and I think it's a completely foreign reference to every poster in this forum. AFAICT this was a made up by the author of the original tweet. I'd like to see it changed to something a bit more familiar, perhaps along the lines of "East Atlantic Monsoon Trough". However, I want to get some input, especially from the OP of this thread.

[drezee]

The current east Atlantic monsoon trough pattern (i.e. an active east Atlantic ITCZ) is not all that uncommon, although I should read up on it more to get a better handle on its intaseasonal variability and duration. For instance, how long does this pattern last compared to say a CAG pattern? How is it impacted (perhaps even inititated?) by WWBs via equatorial (trapped) CCKW waves, the MJO, etc. etc. As already alluded to, the pre-existing broad band of low level convergence/vorticity often interacts with AEWs departing the coast of Africa to induce "Cape Verde" tropical cyclogenesis, especially as we get into the teeth of the CV/MDR season. Pretty easy to visualize this.

Also wondering how best to handle this thread. We should probably limit discussion in this thread to the pattern itself, and keep the threads for individual waves that (may) interact with it separate. Finally, I'm not a big fan of the "Leading Tail" colloquialism in the thread title. I've never seen it used in any sort of discussion (let alone paper), and I think it's a completely foreign reference to every poster in this forum. AFAICT this was a made up by the author of the original tweet. I'd like to see it changed to something a bit more familiar, perhaps along the lines of "East Atlantic Monsoon Trough". However, I want to get some input, especially from the OP of this thread.

AJ,
I definitely understand the thought. I have been around for a while. This is a term I lifted from John Hope many years ago. I have not heard it or seen it elsewhere. I have always liked the term. It is a more a product of the ITCZ trough being lifted N. This would in some defintions constitute the use of monsoon as the winds are against the prevailing flow. I am ok with changing the name but this is a transient feature that will eventually end. Waves are typically lost in the trough. It will be fun to watch.

[AJC3]

AJ,

I definitely understand the thought. I have been around for a while. This is a term I lifted from John Hope many years ago. I have not heard it or seen it elsewhere. I have always liked the term. It is a more a product of the ITCZ trough being lifted N. This would in some defintions constitute the use of monsoon as the winds are against the prevailing flow. I am ok with changing the name but this is a transient feature that will eventually end. Waves are typically lost in the trough. It will be fun to watch.

No worries, and thanks for the reply. I certainly won't demand that it be changed...and it's good to learn how and where you first heard that phrase being used.

[drezee]

AJ,

I definitely understand the thought. I have been around for a while. This is a term I lifted from John Hope many years ago. I have not heard it or seen it elsewhere. I have always liked the term. It is a more a product of the ITCZ trough being lifted N. This would in some defintions constitute the use of monsoon as the winds are against the prevailing flow. I am ok with changing the name but this is a transient feature that will eventually end. Waves are typically lost in the trough. It will be fun to watch.

No worries, and thanks for the reply. I certainly won't demand that it be changed...and it's good to learn how and where you first heard that phrase being used.

Sidenote: I have some old VHS tapes from TWC with John Hope and a young Jim Cantore. 1995 IRIS, Humberto, and Luis is classic

[USTropics]

I'd have to do some more research, but looking at previous seasons where this feature develops, it appears to be a reaction to the sudden change in the trade winds, particularly along the convergence zone where the trade winds originate from the northeast. Here are observed wind vector anomalies from June 20th to July 7th 2020 for Africa And the eastern Atlantic:

(almost uniform easterly flow from Africa - Atlantic)



In the past 3-4 days, this flow has become disrupted (the decrease in easterly flow has allowed for convection along the ITCZ/African monsoon to also creep north, as Aric alluded to earlier today):


According to the GFS and ECMWF forecasts, this should continue for the next 1-2 weeks:



Recently it looks like the last week of August in 2018, the last week of July 2010, and the first week of September 2017 show similar patterns (enhanced trade winds from the east relax, and in some cases westerly flow is seen):

[Aric Dunn]

I'd have to do some more research, but looking at previous seasons where this feature develops, it appears to be a reaction to the sudden change in the trade winds, particularly along the convergence zone where the trade winds originate from the northeast. Here are observed wind vector anomalies from June 20th to July 7th 2020 for Africa And the eastern Atlantic:

(almost uniform easterly flow from Africa - Atlantic)
https://i.imgur.com/ze5rOLU.gif
https://i.imgur.com/94s0REu.gif

In the past 3-4 days, this flow has become disrupted (the decrease in easterly flow has allowed for convection along the ITCZ/African monsoon to also creep north, as Aric alluded to earlier today):
https://i.imgur.com/iE3TYsz.gif

According to the GFS and ECMWF forecasts, this should continue for the next 1-2 weeks:
https://i.imgur.com/1iAyHML.gif
https://i.imgur.com/ckHkMMT.gif

Recently it looks like the last week of August in 2018, the last week of July 2010, and the first week of September 2017 show similar patterns (enhanced trade winds from the east relax, and in some cases westerly flow is seen):
https://i.imgur.com/zWISbA0.gif
https://i.imgur.com/F1TlFSi.gif
https://i.imgur.com/rNCOjvf.gif

Interesting.

Can you find out if those time periods correspond to wet periods in the Sahel regions of Africa ( happens to be the SAL producing regions) ?

I would imagine if the flow had any southerly component that it would produce rain in otherwise dry regions.

I will check what year the Southern Saharan Flower Blooms occurred and when, to see if they correspond to this feature as well.

An interesting note...

the Atacama desert in Chile and Peru have Flower blooms that occur during El nino years.

I wonder if La Nina years correlate to late-season Blooms in the Sahara. ???

[cycloneye]

Is happening.

[drezee]

Is happening.

https://i.imgur.com/5UUtwvl.gif

Looks like it...this wave is consolidating the "tail" now. Typically, one wave will sweep the SAL and another develops behind...

[USTropics]

I'd have to do some more research, but looking at previous seasons where this feature develops, it appears to be a reaction to the sudden change in the trade winds, particularly along the convergence zone where the trade winds originate from the northeast. Here are observed wind vector anomalies from June 20th to July 7th 2020 for Africa And the eastern Atlantic:

(almost uniform easterly flow from Africa - Atlantic)
https://i.imgur.com/ze5rOLU.gif
https://i.imgur.com/94s0REu.gif

In the past 3-4 days, this flow has become disrupted (the decrease in easterly flow has allowed for convection along the ITCZ/African monsoon to also creep north, as Aric alluded to earlier today):
https://i.imgur.com/iE3TYsz.gif

According to the GFS and ECMWF forecasts, this should continue for the next 1-2 weeks:
https://i.imgur.com/1iAyHML.gif
https://i.imgur.com/ckHkMMT.gif

Recently it looks like the last week of August in 2018, the last week of July 2010, and the first week of September 2017 show similar patterns (enhanced trade winds from the east relax, and in some cases westerly flow is seen):
https://i.imgur.com/zWISbA0.gif
https://i.imgur.com/F1TlFSi.gif
https://i.imgur.com/rNCOjvf.gif

Interesting.

Can you find out if those time periods correspond to wet periods in the Sahel regions of Africa ( happens to be the SAL producing regions) ?

I would imagine if the flow had any southerly component that it would produce rain in otherwise dry regions.

I will check what year the Southern Saharan Flower Blooms occurred and when, to see if they correspond to this feature as well.

An interesting note...

the Atacama desert in Chile and Peru have Flower blooms that occur during El nino years.

I wonder if La Nina years correlate to late-season Blooms in the Sahara. ???

Here are some animated transitions I made (10 days prior of the event, 10 days during, and 10 days after):

[drezee]

Yes, the front was indeed a sacrifice for the wave behind...