Reflections on What Happened to the Worldwide Tropics After September 2021

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Reflections on What Happened to the Worldwide Tropics After September 2021

#1 Postby Category5Kaiju » Sat Nov 20, 2021 9:37 am

I felt the need to start a new thread on this particular topic given it is not just the Atlantic basin as the sst indicators thread typically covers but literally the entire world. In addition, the events we are seeing are just so anomalous, with zero major strength cyclones since the past two months, no hurricane-strength systems also occurring since Malou, and with models not really showing much in the near future, that I'd have to imagine there's going to be extensive retrospective research, not to mention long-winded talks between us weather enthusiasts on what on earth happened. I mean, even 1977 and 2013 were not this unfavorable worldwide, particularly late-season as the WPAC still produced strong November TCs. It's one thing for the WPAC to become active and produce powerful TCs late season while the other basins become inactive, but even that is not happening oddly.

I frankly do not know how long this thread will become, but I will say that discussions on why we are seeing what we are seeing now would really be helpful to understand what to expect going forward into future seasons; therefore, what are your guys' personal thoughts on what could be contributing to such a dead worldwide tropics?
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#2 Postby Yellow Evan » Sat Nov 20, 2021 4:10 pm

La Niña and an unfavorable mid-latitude pattern.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#3 Postby Iceresistance » Sat Nov 20, 2021 4:33 pm

Yellow Evan wrote:La Niña and an unfavorable mid-latitude pattern.


And MJO becomes inactive as well.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#4 Postby Hammy » Sat Nov 20, 2021 6:29 pm

A bit off topic, but given the atmosphere is not behaving at all like La Nina (at least in the Atlantic side) and we may have had another 2013-type incident, I wonder if like 2013, this could lead to a much colder than forecast winter for the Southeast.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#5 Postby aspen » Sat Nov 20, 2021 6:46 pm

Yellow Evan wrote:La Niña and an unfavorable mid-latitude pattern.

Yeah but if this happened to be a chance occurrence of the two happening at the same time, then why hasn’t a global TCG shutdown like this been seen before? This is the first time in decades that no MH has existed anywhere in the Northern Hemisphere after September; 2013 still produced Raymond and Haiyan despite its THC collapse. Whatever has happened is rarer than two weather patterns randomly occurring simultaneously.

Another important question is: how long will whatever is going on last? Like Hammy suggested, it could have impacts on winter weather forecasts for different regions, and if this unusual state persists long enough, it could cause a delayed start to the 2022 Atlantic season.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#6 Postby Yellow Evan » Sat Nov 20, 2021 9:42 pm

aspen wrote:
Yellow Evan wrote:La Niña and an unfavorable mid-latitude pattern.

Yeah but if this happened to be a chance occurrence of the two happening at the same time, then why hasn’t a global TCG shutdown like this been seen before? This is the first time in decades that no MH has existed anywhere in the Northern Hemisphere after September; 2013 still produced Raymond and Haiyan despite its THC collapse. Whatever has happened is rarer than two weather patterns randomly occurring simultaneously.

Another important question is: how long will whatever is going on last? Like Hammy suggested, it could have impacts on winter weather forecasts for different regions, and if this unusual state persists long enough, it could cause a delayed start to the 2022 Atlantic season.


Because it’s a low chance occurrence. That doesn’t mean it won’t ever happen; just is unlikely and this year happened to be a case where a statistically unlike event happened.

A THC collapse wouldn’t really hinder other basins negatively and even such collapse wouldn’t occur in one year. While a gradual THC slowdown is likely as the AMOC weakens over the next several decades and this would favor a -AMO configuration as more warm waters get stuck in the Gulfstream, I don’t think a true -AMO flip is likely to be in occurring as those generally occur alongside El Niño events and a change in the configuration of the NAO (with + generally favoring -AMO and visa versa).
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#7 Postby AnnularCane » Sat Nov 20, 2021 10:54 pm

Does ANYONE know what's going on? I mean, has there been any kind of discussion about it elsewhere?
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#8 Postby Ptarmigan » Mon Nov 22, 2021 10:32 pm

I wonder why the season just shutdown after it was an active one.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#9 Postby hurricanes1234 » Tue Nov 23, 2021 8:39 am

AnnularCane wrote:Does ANYONE know what's going on? I mean, has there been any kind of discussion about it elsewhere?


It seems not because outside our discussions on this forum and maybe one or two posts on Twitter, I haven't seen anything about it anywhere and it appears as though in the media, there's more focus on the list of names being used up than the mysterious background issues which plagued the entire season and caused extremely long intervals of nothing, many or most systems struggling and ultimately this early halt.

IMO years like this one show why it's important not to judge a season's activity only by its numbers. Especially in a time where technology is so much better than even a few years ago and allows us to detect borderline tropical cyclones that cause us to use up names faster.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#10 Postby MarioProtVI » Thu Nov 25, 2021 12:37 pm

In the Atlantic’s case it was largely due to the Atlantic Niño - it suppressed the ITCZ further south to the point where waves just ran into South America and not into the Caribbean, preventing any activity there. MJO might’ve been a factor too.

EPac was just the La Niña creating not so favorable conditions (but probably larger then expected given the two storms fell short of expectations for their conditions, especially Pamela), plus October is when things start shutting down there.

The big question mark then is the WPac which was almost dead quiet the entire past two months which are some of the most active and favorable months usually for the basin. I think there should be a extensive study to determine why the WPac just was dead silent during its peak.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#11 Postby aspen » Thu Nov 25, 2021 12:55 pm

MarioProtVI wrote:In the Atlantic’s case it was largely due to the Atlantic Niño - it suppressed the ITCZ further south to the point where waves just ran into South America and not into the Caribbean, preventing any activity there. MJO might’ve been a factor too.

EPac was just the La Niña creating not so favorable conditions (but probably larger then expected given the two storms fell short of expectations for their conditions, especially Pamela), plus October is when things start shutting down there.

The big question mark then is the WPac which was almost dead quiet the entire past two months which are some of the most active and favorable months usually for the basin. I think there should be a extensive study to determine why the WPac just was dead silent during its peak.

What’s even stranger is how it was dead after September despite producing a 165 kt T#8.0 Super Typhoon in April of all months. For a Nina year, it’s more likely that the WPac’s single ultra-intense system would be something near the Philippines in October or November like Goni ‘20, Megi ‘10, or Zeb ‘98.

This entire year was strange across all NHem basins and will probably be the subject of further study for years. Perhaps the impacts on various circulation systems like the Gulf Stream and THC by anthropogenic climate change could lead to an increase in “bust years” where TCG shuts off in one or multiple basins despite climo saying it should have. When atmospheric conditions are right, though, then there could be more “boom years” where multiple systems take advantage of warmer SSTs.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#12 Postby zzh » Thu Nov 25, 2021 2:21 pm

Why the Atlantic is dead in October.
First week: Shear is everywhere
Image
Rest of October: Crazy ridge enhanced by warm sst buried all the waves in South America
Image
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#13 Postby zzh » Thu Nov 25, 2021 2:39 pm

aspen wrote:
MarioProtVI wrote:In the Atlantic’s case it was largely due to the Atlantic Niño - it suppressed the ITCZ further south to the point where waves just ran into South America and not into the Caribbean, preventing any activity there. MJO might’ve been a factor too.

EPac was just the La Niña creating not so favorable conditions (but probably larger then expected given the two storms fell short of expectations for their conditions, especially Pamela), plus October is when things start shutting down there.

The big question mark then is the WPac which was almost dead quiet the entire past two months which are some of the most active and favorable months usually for the basin. I think there should be a extensive study to determine why the WPac just was dead silent during its peak.

What’s even stranger is how it was dead after September despite producing a 165 kt T#8.0 Super Typhoon in April of all months. For a Nina year, it’s more likely that the WPac’s single ultra-intense system would be something near the Philippines in October or November like Goni ‘20, Megi ‘10, or Zeb ‘98.

This entire year was strange across all NHem basins and will probably be the subject of further study for years. Perhaps the impacts on various circulation systems like the Gulf Stream and THC by anthropogenic climate change could lead to an increase in “bust years” where TCG shuts off in one or multiple basins despite climo saying it should have. When atmospheric conditions are right, though, then there could be more “boom years” where multiple systems take advantage of warmer SSTs.

I am not surprised that the WPac is dead. In double peak La Nina years like 2010, 2008, 1999, WPac is usually dead in OND.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#14 Postby Shell Mound » Fri Nov 26, 2021 4:34 am

Image

Note the southward-displaced ULAC in the equatorial Atlantic, along with the dual TUTTs at 50°W and 80°W, respectively. By contrast, deep-layer shear over the EPAC was minimal. However, the strong ULAC near 130°W is typical of Niñas during October, so the background state does reflect Niña conditions, at least in part. The Atlantic Niño and correspondingly suppressed ITCZ likely played a role in hindering TC genesis in the Atlantic during October. However, the warm subtropics, fuelled in part by climate change via a weakened AMOC, likely exacerbated the effects of the Atlantic Niño by contributing to enhanced shear over the western MDR and Caribbean. So I think the combination of the Atlantic Niño and climate change-linked feedback likely contributed to the inactive October in the Atlantic basin.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#15 Postby dexterlabio » Fri Nov 26, 2021 7:06 am

zzh wrote:
aspen wrote:
MarioProtVI wrote:In the Atlantic’s case it was largely due to the Atlantic Niño - it suppressed the ITCZ further south to the point where waves just ran into South America and not into the Caribbean, preventing any activity there. MJO might’ve been a factor too.

EPac was just the La Niña creating not so favorable conditions (but probably larger then expected given the two storms fell short of expectations for their conditions, especially Pamela), plus October is when things start shutting down there.

The big question mark then is the WPac which was almost dead quiet the entire past two months which are some of the most active and favorable months usually for the basin. I think there should be a extensive study to determine why the WPac just was dead silent during its peak.

What’s even stranger is how it was dead after September despite producing a 165 kt T#8.0 Super Typhoon in April of all months. For a Nina year, it’s more likely that the WPac’s single ultra-intense system would be something near the Philippines in October or November like Goni ‘20, Megi ‘10, or Zeb ‘98.

This entire year was strange across all NHem basins and will probably be the subject of further study for years. Perhaps the impacts on various circulation systems like the Gulf Stream and THC by anthropogenic climate change could lead to an increase in “bust years” where TCG shuts off in one or multiple basins despite climo saying it should have. When atmospheric conditions are right, though, then there could be more “boom years” where multiple systems take advantage of warmer SSTs.

I am not surprised that the WPac is dead. In double peak La Nina years like 2010, 2008, 1999, WPac is usually dead in OND.



For real though...I always thought WPAC can go bonkers every last quarter of a La Niña year. Then I realized years like 2011, 1999, 2017, and 2021 have 1 thing in common: they are all second year of consecutive La Niñas. So I fully accept the basin's duddery esp. in OND period. Not every La Niña year is a 1998, 2010, or 2016. ;) The fact that WPAC had Surigae and Chanthu are only a bonus.


As for the Atlantic....the quietness since Oct is definitely unusual especially in a year that it is supposed to stand out (cold ENSO to La Niña)...no El Niño to kill the season way too early. Nonetheless, the basin pulled off yet another impressive season with Grace, Ida, and Sam. But the season could have been a lot more, I must say.
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Re: Reflections on What Happened to the Worldwide Tropics After September 2021

#16 Postby Ptarmigan » Sun Nov 28, 2021 9:46 pm

I notice West Pacific tends to be less active in years when El Nino transition to La Nina. There have been active West Pacific seasons in La Nina like in 1996. 1996 was a weak La Nina. Interestingly, East Pacific was inactive in 1996.

http://tropical.atmos.colostate.edu/Rea ... estpacific
http://tropical.atmos.colostate.edu/Rea ... astpacific
http://tropical.atmos.colostate.edu/Rea ... thatlantic
http://tropical.atmos.colostate.edu/Rea ... loc=global

1977 was inactive in the Northern Hemisphere, while it was average in the Southern Hemisphere.
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