Scenarios for a Hyperactive or Minimally Active Atlantic Season

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Scenarios for a Hyperactive or Minimally Active Atlantic Season

#1 Postby AlphaToOmega » Thu Oct 21, 2021 5:22 pm

Here are some hypothetical scenarios that probably will not happen in my lifetime; it is fun to think about the possibilities of such scenarios occurring and what conditions would be required (no relation to the wiki)

Scenario 1 (neutered 1914): a North Atlantic hurricane season without any storms whatsoever
Scenario 2 (anti-1914): a maximally active North Atlantic hurricane season (probably 36 storms, 18 hurricanes, 9 major hurricanes, and 300 ACE)

My thoughts:
Scenario 1 would likely require:
  1. A really negative AMO (below -1 C)
  2. A really cold MDR (below -1 C)
  3. A strong El Nino (above 1.5 C)
  4. An American Standing Wave
  5. Persistent +VP anomalies in Africa and the Indian Ocean
  6. Strong persistent SAL outbreaks from June to October
  7. Strong persistent TUTTs induced by recurving typhoons

Scenario 2 would likely require:
  1. A really positive AMO (above 1 C)
  2. A record-breaking MDR (above 1 C)
  3. A strong La Nina (below -1.5 C)
  4. An African Standing Wave
  5. Very few to no SAL outbreaks
  6. No recurving typhoons inducing TUTTs
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#2 Postby Yellow Evan » Thu Oct 21, 2021 7:12 pm

Scenario 1 is very difficult to achieve because despite even in years where AEW genesis is shut off due to some combination of -AMO/dry Sahel/El Niño, those factors don’t necessarily favor activity outside the deep tropics, which is often good for at least a few at least subtropical if not fully tropical cyclones. This is more or less what already happened in 1983 and what probably happened in 1914.

Scenario 2 is a little more feasible than one might think in theory but keep in mind as we saw at times the last year or so, too strong of a West African Monsoon can result in the presence of a monsoon trough, resulting in broader systems that take days to organize and can also result in higher shear vis the TEJ. Also not sure if the strength of a La Nina really matters much, as we’ve seen years like 2007 and parts of 2010 still have TUTT induced shear despite their record breaking strength.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#3 Postby aspen » Thu Oct 21, 2021 7:52 pm

Yellow Evan wrote:Scenario 1 is very difficult to achieve because despite even in years where AEW genesis is shut off due to some combination of -AMO/dry Sahel/El Niño, those factors don’t necessarily favor activity outside the deep tropics, which is often good for at least a few at least subtropical if not fully tropical cyclones. This is more or less what already happened in 1983 and what probably happened in 1914.

Scenario 2 is a little more feasible than one might think in theory but keep in mind as we saw at times the last year or so, too strong of a West African Monsoon can result in the presence of a monsoon trough, resulting in broader systems that take days to organize and can also result in higher shear vis the TEJ. Also not sure if the strength of a La Nina really matters much, as we’ve seen years like 2007 and parts of 2010 still have TUTT induced shear despite their record breaking strength.

To add on, scenario 2 would likely require an ASW and ITCZ setup like this year: a strong standing wave that isn’t too strong to the point where every wave is too broad, and a low ITCZ that keeps these waves south and over warm waters for longer. Even with such an MJO-dependent background state, 2021 still managed to produce two 30-60 ACE MDR majors that developed east of 40W; Elsa and Grace were also notable hurricanes that developed from low-latitude waves, although both were weak for most of their lives. Scenario 2 would also need a 2020-like background state, where storms are easily able to form and activity isn’t so reliant on a perfect MJO phase.

2021 has shown that while the ASW and ITCZ can be forecast out in advance with reasonable accuracy (forecasts for another strong ASW and a lower ITCZ than 2020 both verified well), background state and MJO dependency is something we probably won’t be able to know until the season is already ongoing.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#4 Postby Category5Kaiju » Fri Oct 22, 2021 4:36 pm

AlphaToOmega wrote:Here are some hypothetical scenarios that probably will not happen in my lifetime; it is fun to think about the possibilities of such scenarios occurring and what conditions would be required (no relation to the wiki)

Scenario 1 (neutered 1914): a North Atlantic hurricane season without any storms whatsoever
Scenario 2 (anti-1914): a maximally active North Atlantic hurricane season (probably 36 storms, 18 hurricanes, 9 major hurricanes, and 300 ACE)

My thoughts:
Scenario 1 would likely require:
  1. A really negative AMO (below -1 C)
  2. A really cold MDR (below -1 C)
  3. A strong El Nino (above 1.5 C)
  4. An American Standing Wave
  5. Persistent +VP anomalies in Africa and the Indian Ocean
  6. Strong persistent SAL outbreaks from June to October
  7. Strong persistent TUTTs induced by recurving typhoons

Scenario 2 would likely require:
  1. A really positive AMO (above 1 C)
  2. A record-breaking MDR (above 1 C)
  3. A strong La Nina (below -1.5 C)
  4. An African Standing Wave
  5. Very few to no SAL outbreaks
  6. No recurving typhoons inducing TUTTs


Here's my personal take:

Scenario 2 would most likely require:
- A really positive AMO (above 1.5-2 C)
- An anomalously warm MDR (above 1.5-2 C)
- A weak La Nina (-0.5 to -0.9 C)
- An African Standing Wave that is not too weak but also not too potent
- Very weak SAL outbreaks, with summer outbreaks being as weak as typical September outbreaks
- A dead WPAC and EPAC, with rising motion (favorable MJO) being positioned in 2-4 for lengthy periods of time
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#5 Postby al78 » Fri Oct 22, 2021 5:19 pm

Scenario 2 sounds a bit like a combination of 2004 and 2005. The former had high activity in the tropical Atlantic and multiple destructive landfalls thanks to storms being steered westward at low latitiudes (upper level ridging over the US east coast). The latter had very high activity on the west side of the basin, the Caribbean and Gulf, but the MDR activity was mediocre. How about we take the conditions that made August and September 2004 hyperactive, and the conditions that made July and October-December 2005 hyperactive (or maybe substitute conditions in autumn 2005 with autumn 2020), and put them together. If is was theoretically possible to get optimal conditions in every month of the hurricane season like that, the season's ACE would be enormous, and so would the U.S. economic losses.

As for 1914, are we sure there was only one storm in the entire season? Can we be confident to high probability there were no two day short lived storms out at sea well away from land and shipping?
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#6 Postby Shell Mound » Sat Oct 23, 2021 3:55 am

This thread is a bit similar to this one. In the latter I attempted to delineate the most realistic “ceiling” for a hyperactive Atlantic season in terms of overall intensity and impact(s). As far as ACE generated seasonally and over land is concerned, by all available indications the 1933 season was one of the most extreme on record. It likely featured at least eight major hurricanes and multiple long-trackers in the MDR and Caribbean, including two (plausible) Category-4 impacts on the CONUS within 24h of each other. Not only was the season likely on a par with 2005 in terms of overall NS, but it also featured a strong westward bias in its tracks, to not mention extremely high ACE that is almost certainly underestimated. 1933’s parameters in the deep tropics—including ENSO, MSLP, and low vertical wind shear—actually surpassed 2005’s, and its SST in the MDR and Caribbean were comparable. Had 1933 occurred today, we would likely be talking about how it surpassed 2005 in virtually all areas, especially in terms of a CV season.

As far as scenario number two is concerned, a number of seasons in the late 1800s met those criteria. For instance, look at the SST configuration in 1878:

Image

The outcome, per preliminary reanalysis (map courtesy of TheAustinMan):

Image

Note that, per reanalysis, 1878 featured a 130-kt, 927-mb Category 4 in the central MDR during mid to late October.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#7 Postby MarioProtVI » Sat Oct 23, 2021 2:35 pm

Shell Mound wrote:This thread is a bit similar to this one. In the latter I attempted to delineate the most realistic “ceiling” for a hyperactive Atlantic season in terms of overall intensity and impact(s). As far as ACE generated seasonally and over land is concerned, by all available indications the 1933 season was one of the most extreme on record. It likely featured at least eight major hurricanes and multiple long-trackers in the MDR and Caribbean, including two (plausible) Category-4 impacts on the CONUS within 24h of each other. Not only was the season likely on a par with 2005 in terms of overall NS, but it also featured a strong westward bias in its tracks, to not mention extremely high ACE that is almost certainly underestimated. 1933’s parameters in the deep tropics—including ENSO, MSLP, and low vertical wind shear—actually surpassed 2005’s, and its SST in the MDR and Caribbean were comparable. Had 1933 occurred today, we would likely be talking about how it surpassed 2005 in virtually all areas, especially in terms of a CV season.

As far as scenario number two is concerned, a number of seasons in the late 1800s met those criteria. For instance, look at the SST configuration in 1878:

https://i.ibb.co/PD7tR8S/1878-ASOSSTA-1.png

The outcome, per preliminary reanalysis (map courtesy of TheAustinMan):

https://i.imgur.com/KrgJ1Ur.png

Note that, per reanalysis, 1878 featured a 130-kt, 927-mb Category 4 in the central MDR during mid to late October.

How the hell 1878 managed to basically get a Lorenzo/Sam-like storm in a time period where the MDR is basically done for the season with high wind shear being established is beyond my understanding if this reanalysis is correct. Record warm MDR? Record breaking MJO pulse that reduced wind shear by an unusually historic amount in that area? That is probably the biggest anomaly I’ve ever seen and probably more so then Tomas 2010 reaching C2 on the extreme western edge of the MDR in late October.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#8 Postby Shell Mound » Sat Oct 23, 2021 3:00 pm

MarioProtVI wrote:
Shell Mound wrote:This thread is a bit similar to this one. In the latter I attempted to delineate the most realistic “ceiling” for a hyperactive Atlantic season in terms of overall intensity and impact(s). As far as ACE generated seasonally and over land is concerned, by all available indications the 1933 season was one of the most extreme on record. It likely featured at least eight major hurricanes and multiple long-trackers in the MDR and Caribbean, including two (plausible) Category-4 impacts on the CONUS within 24h of each other. Not only was the season likely on a par with 2005 in terms of overall NS, but it also featured a strong westward bias in its tracks, to not mention extremely high ACE that is almost certainly underestimated. 1933’s parameters in the deep tropics—including ENSO, MSLP, and low vertical wind shear—actually surpassed 2005’s, and its SST in the MDR and Caribbean were comparable. Had 1933 occurred today, we would likely be talking about how it surpassed 2005 in virtually all areas, especially in terms of a CV season.

As far as scenario number two is concerned, a number of seasons in the late 1800s met those criteria. For instance, look at the SST configuration in 1878:

https://i.ibb.co/PD7tR8S/1878-ASOSSTA-1.png

The outcome, per preliminary reanalysis (map courtesy of TheAustinMan):

https://i.imgur.com/KrgJ1Ur.png

Note that, per reanalysis, 1878 featured a 130-kt, 927-mb Category 4 in the central MDR during mid to late October.

How the hell 1878 managed to basically get a Lorenzo/Sam-like storm in a time period where the MDR is basically done for the season with high wind shear being established is beyond my understanding if this reanalysis is correct. Record warm MDR? Record breaking MJO pulse that reduced wind shear by an unusually historic amount in that area? That is probably the biggest anomaly I’ve ever seen and probably more so then Tomas 2010 reaching C2 on the extreme western edge of the MDR in late October.

The reanalysed best track for 1851–98 can be found here. Simply click on “Supplementary Materials” and then click on the ZIP file (the revised HURDAT should be in Excel-type format). In general, the late nineteenth century featured a number of seasons with record-low vertical wind shear, combined with a robust +AMO and -ENSO, as the SST configuration for 1878 alone, posted previously, implied:

In addition to the increased uncertainty early in the record, we note that 20CRv3 also identifies extremely low vertical wind shear in the late 1800s—a time period which had several very active Atlantic hurricane seasons, especially 1878, 1886, 1887, and 1893.

According to the revised data, Storm #14 (previously #10) of 1878 attained TS status at 18.2°N 19.2°W at 12:00 UTC on 10 October. The TC became a hurricane one day later, at 18.6°N 25°W, just before a ship registered a central MSLP of 979 mb. At 06:00 UTC on 14 October, while the storm was centred at 17.6°N 41.1°W, a ship at an unknown distance from the eye recorded a MSLP of 948 mb, suggesting MSW of ≥ 115 kt, per P/W relationships (the BT file lists 100 kt at that point, but P/W would suggest an even higher MSW value). At 00:00 UTC on 17 October, while the TC was centred near 22.3°N 47.5°W, yet another ship at an unknown distance from the eye registered a MSLP of 927 mb, indicating MSW of ≥ 130 kt. At 12:00 UTC on 18 October a fourth ship measured a MSLP of 951 mb in the eye, which is consistent with the other observations mentioned thus far, so the available observations do appear to support the existence of a powerful MH in the east-central MDR during mid to late October of 1878.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#9 Postby Ptarmigan » Sun Oct 24, 2021 12:09 pm

al78 wrote:Scenario 2 sounds a bit like a combination of 2004 and 2005. The former had high activity in the tropical Atlantic and multiple destructive landfalls thanks to storms being steered westward at low latitiudes (upper level ridging over the US east coast). The latter had very high activity on the west side of the basin, the Caribbean and Gulf, but the MDR activity was mediocre. How about we take the conditions that made August and September 2004 hyperactive, and the conditions that made July and October-December 2005 hyperactive (or maybe substitute conditions in autumn 2005 with autumn 2020), and put them together. If is was theoretically possible to get optimal conditions in every month of the hurricane season like that, the season's ACE would be enormous, and so would the U.S. economic losses.

As for 1914, are we sure there was only one storm in the entire season? Can we be confident to high probability there were no two day short lived storms out at sea well away from land and shipping?


1933 was likely more active than 2004 and 2005. Other seasons I suspect were just as active are 1878, 1886, 1893, and 1926.

Years with hyperactive hurricane seasons had year start with El Nino and than transitioned to La Nina. 2004 had a weak El Nino.

1914 is largely uncertain. 1962, 1977, 1983, and 2013 were inactive. 1962, 1983, and 2013 were transitioning into La Nina. 1977 started with El Nino and faded only to come back again. The entire Northern Hemipshere had below average season in 1977.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#10 Postby Yellow Evan » Sun Oct 24, 2021 2:13 pm

2013 was not a La Niña. 1914 was a multi-year El Niño and while calling 1983 a La Niña is a bit of a stretch; very warm SSTs remained in the eastern Pacific even after the El Niño had officially dissipated so the atmosphere reassembled an El Niño for significant time thereafter.

Let’s pause the breaks on 1878 being a 2005-esque season as well, considering it was coming off the strongest El Niño in history had come right before it, so it likely was very back heavy like 1998 and 2016.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#11 Postby aspen » Sun Oct 24, 2021 3:02 pm

This October would seem to suggest that strong ridging and a low-latitude ITCZ are not as conductive for an intense and dangerous year as previously expected, because that seems to be at least one of the reasons why the last few weeks have been dead: all the waves that would’ve developed in the WCar get shoved over South America and don’t develop until they reach the EPac. During August and September, it would have the potential for a 2004/2017-like season; in October and November, it could shut off activity for a time. For a season to see maximum levels of activity consistently throughout August through October, there would have to be a perfect balance of ridging and ITCZ latitude that would be very hard to achieve alongside a favorable background state, correct ENSO phase/progression, and mostly favorable MJOs.

Another 30+ NS year would require so many perfect environmental and sub-seasonal characteristics that one is quite unlikely to occur for at least another decade. It would need a background state, ENSO progression, and SSTA configuration like 2020, but an ASW/WAM magnitude, ITCZ latitude, and tropical wave amplitude like 2021. Waves would also need to follow paths similar to JAS 2021 and ON 2020 for a season to reach peak potential. That’s just so hard to achieve, thankfully.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#12 Postby Shell Mound » Tue Oct 26, 2021 11:28 am

Yellow Evan wrote:Let’s pause the breaks on 1878 being a 2005-esque season as well, considering it was coming off the strongest El Niño in history had come right before it, so it likely was very back heavy like 1998 and 2016.

Image

Never say never. :wink: 1878 coincided with the lowest vertical wind shear in the MDR on record since records began in 1836. Also, the SST configuration was that of a very strong +AMO, with a cool Gulf of Guinea favouring upward motion over West Africa. Note that by ASO +ENSO conditions had already vanished. Besides, as mentioned previously, the reanalysis found at least four—likely five or more—hurricanes in the MDR during 1878, including the infamous “Lorenzo”/“Sam” redux in mid to late October. Given pre-satellite, pre-reconnaissance shortcomings, I think that 1878 could have easily rivalled 2005 or 1933 in terms of ACE, if not total NS (especially if the current naming standards were applied).
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#13 Postby tolakram » Tue Oct 26, 2021 11:48 am

Shell Mound wrote:
Yellow Evan wrote:Let’s pause the breaks on 1878 being a 2005-esque season as well, considering it was coming off the strongest El Niño in history had come right before it, so it likely was very back heavy like 1998 and 2016.

https://i.ibb.co/HHxHJ3b/1878-MDRVWS-1.jpg

Never say never. :wink: 1878 coincided with the lowest vertical wind shear in the MDR on record since records began in 1836. Also, the SST configuration was that of a very strong +AMO, with a cool Gulf of Guinea favouring upward motion over West Africa. Note that by ASO +ENSO conditions had already vanished. Besides, as mentioned previously, the reanalysis found at least four—likely five or more—hurricanes in the MDR during 1878, including the infamous “Lorenzo”/“Sam” redux in mid to late October. Given pre-satellite, pre-reconnaissance shortcomings, I think that 1878 could have easily rivalled 2005 or 1933 in terms of ACE, if not total NS (especially if the current naming standards were applied).


How was vertical wind shear measured over the MDR in 1878?
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#14 Postby Shell Mound » Tue Oct 26, 2021 11:52 am

tolakram wrote:
Shell Mound wrote:
Yellow Evan wrote:Let’s pause the breaks on 1878 being a 2005-esque season as well, considering it was coming off the strongest El Niño in history had come right before it, so it likely was very back heavy like 1998 and 2016.

https://i.ibb.co/HHxHJ3b/1878-MDRVWS-1.jpg

Never say never. :wink: 1878 coincided with the lowest vertical wind shear in the MDR on record since records began in 1836. Also, the SST configuration was that of a very strong +AMO, with a cool Gulf of Guinea favouring upward motion over West Africa. Note that by ASO +ENSO conditions had already vanished. Besides, as mentioned previously, the reanalysis found at least four—likely five or more—hurricanes in the MDR during 1878, including the infamous “Lorenzo”/“Sam” redux in mid to late October. Given pre-satellite, pre-reconnaissance shortcomings, I think that 1878 could have easily rivalled 2005 or 1933 in terms of ACE, if not total NS (especially if the current naming standards were applied).

How was vertical wind shear measured over the MDR in 1878?

Atmospheric data are calculated from 20CRv3 (Slivinski et al. 2019). This dataset is available every 3 h from 1836 to 2015. It uses an ensemble Kalman filter (EnKF) methodology with 80 members and the NOAA Global Forecast System model to generate the needed first guess fields. ... The 20CRv3 dataset is an improvement upon earlier versions of the Twentieth Century Reanalysis (Compo et al. 2011) due to a higher-resolution model forcing the new reanalysis, improved data assimilation methods, an increased ensemble size, and an increased number of surface pressure observations.

Source
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#15 Postby tolakram » Tue Oct 26, 2021 11:57 am

Shell Mound wrote:Source



I read the source Shell, the stat is quoted multiple times as fact. The question stands, how was it measured? I can't find any definitive answer.

I see you edited your post.

NOAA Global Forecast System model to generate the needed first guess fields.

So the GFS was used to guess shear. I'll just smile and wave. I don't doubt the stat though. :)
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#16 Postby Shell Mound » Tue Oct 26, 2021 12:01 pm

tolakram wrote:
Shell Mound wrote:Source

I read the source Shell, the stat is quoted multiple times as fact. The question stands, how was it measured? I can't find any definitive answer.

I see you edited your post.

NOAA Global Forecast System model to generate the needed first guess fields.

So the GFS was used to guess shear. I'll just smile and wave. I don't doubt the stat though. :)

Furthermore:
The only synoptic observations used to derive the reanalysis estimates of the full atmosphere at any particular time are surface and sea level pressure reports from land stations, ships, and buoys, as well as TC MSLP values from IBTrACS. Monthly sea ice concentration fields and pentad SST fields are also prescribed as boundary conditions.

So the shear with height is extrapolated.
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#17 Postby Ptarmigan » Mon Nov 01, 2021 7:14 pm

Yellow Evan wrote:2013 was not a La Niña. 1914 was a multi-year El Niño and while calling 1983 a La Niña is a bit of a stretch; very warm SSTs remained in the eastern Pacific even after the El Niño had officially dissipated so the atmosphere reassembled an El Niño for significant time thereafter.

Let’s pause the breaks on 1878 being a 2005-esque season as well, considering it was coming off the strongest El Niño in history had come right before it, so it likely was very back heavy like 1998 and 2016.


2013 had cooler waters in the El Nino region. It had some La Nina like condition, but not outright La Nina. ONI has La Nina by end of 1983 to early 1984. Again, this is one data used for LA Nina/El Nino. I am not suggesting 1983 was a La Nina year in a way. There are so many metrics for El Nino/La Nina.

https://origin.cpc.ncep.noaa.gov/produc ... ONI_v5.php
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#18 Postby Yellow Evan » Tue Nov 02, 2021 4:45 pm

Ptarmigan wrote:
Yellow Evan wrote:2013 was not a La Niña. 1914 was a multi-year El Niño and while calling 1983 a La Niña is a bit of a stretch; very warm SSTs remained in the eastern Pacific even after the El Niño had officially dissipated so the atmosphere reassembled an El Niño for significant time thereafter.

Let’s pause the breaks on 1878 being a 2005-esque season as well, considering it was coming off the strongest El Niño in history had come right before it, so it likely was very back heavy like 1998 and 2016.


2013 had cooler waters in the El Nino region. It had some La Nina like condition, but not outright La Nina. ONI has La Nina by end of 1983 to early 1984. Again, this is one data used for LA Nina/El Nino. I am not suggesting 1983 was a La Nina year in a way. There are so many metrics for El Nino/La Nina.

https://origin.cpc.ncep.noaa.gov/produc ... ONI_v5.php


You are somewhat correct about 2013, looking at MEI as it did briefly cross the La Niña stage. I guess my original point in regards to 1983 is:

Image

This is a strong El Niño like configuration, not a La Nina one. That plus a super dry Africa is why 1983 was dead in addition to the typical -AMO of that era.
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Shell Mound
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Re: Scenarios for a Hyperactive or Minimally Active Atlantic Season

#19 Postby Shell Mound » Wed Nov 03, 2021 4:17 am

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:double:
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