2026 ENSO Updates

[cycloneye]

The IRI multi-model predictions indicate ENSO-neutral will emerge during January-March (JFM) 2026 [Fig. 6]. In conjunction with the North American Multi-Model Ensemble, (NMME) the team favors ENSO-neutral to develop during JFM 2026. Even after equatorial Pacific SSTs transition to ENSO-neutral, La Niña may still have some lingering influence through the early Northern Hemisphere spring 2026 (e.g., CPC's seasonal outlooks). For longer forecast horizons, there are growing chances of El Niño, though there remains uncertainty given the lower accuracy of model forecasts through the spring. In summary, La Niña persists, followed by a 75% chance of a transition to ENSO-neutral during January-March 2026. ENSO-neutral is through at least Northern Hemisphere late spring 2026 [Fig. 7].

https://www.cpc.ncep.noaa.gov/products/ ... disc.shtml

[Yellow Evan]

Dateline or near dateline WWBs aren’t that unheard of this time of year (or even in the December before) in budding El Niños. 1982, 1997, 2002 and 2014 all had them. Definitely a sign of things to come but it isn’t unprecedented like Eric’s tweet implies.

[cycloneye]

CPC mentions some uncertainty because of the spring barrier in terms of El Niño.

[Kingarabian]

Dateline or near dateline WWBs aren’t that unheard of this time of year (or even in the December before) in budding El Niños. 1982, 1997, 2002 and 2014 all had them. Definitely a sign of things to come but it isn’t unprecedented like Eric’s tweet implies.

It's really hard to get a dateline WWB this strong this early. Usually they come in during Feb-May. If this materializes you could call for a strong El Nino this year if the trade pattern/SOI cooperates in MAM.

[Kingarabian]

GFS trending stronger with this upcoming MJO.

[Kingarabian]

The PDO data for december is down to -84 from the november one that was at -1.21.

https://oceanview.pfeg.noaa.gov/erddap/ ... e?time,PDO

Let's see if it finally switches to positive this spring.

[Yellow Evan]

Dateline or near dateline WWBs aren’t that unheard of this time of year (or even in the December before) in budding El Niños. 1982, 1997, 2002 and 2014 all had them. Definitely a sign of things to come but it isn’t unprecedented like Eric’s tweet implies.

It's really hard to get a dateline WWB this strong this early. Usually they come in during Feb-May. If this materializes you could call for a strong El Nino this year if the trade pattern/SOI cooperates in MAM.

I think this current WWB locks in an El Niño even if it’s 2014 esque. Another WWB in the spring would push us towards the stronger camp even if I’m a little cautious just because our last strong El Niño was a mere 3 years ago, but that was also a very unorthodox El Niño.

[Ntxw]

The only period where two fairly significant El Nino's I can see in the ONI index was 1963-1964 (moderate) and 1965-1966 (strong) that were relatively close to each other. It would be pretty rare to have two big ones so close. Even more odd (I know the RONI says differently; I still have debate if we are even using this index correctly/interpretation in terms of identifying its interaction with ENSO via other SSTa outside of it) but I digress, is that by ONI we never achieved official Nina for 2024-2025 and 2025-2026, technically cold-neutral.

To have two solid Ninos in theory with two cold neutrals during a deep -PDO, odd indeed.

[Kingarabian]

The only period where two fairly significant El Nino's I can see in the ONI index was 1963-1964 (moderate) and 1965-1966 (strong) that were relatively close to each other. It would be pretty rare to have two big ones so close. Even more odd (I know the RONI says differently; I still have debate if we are even using this index correctly/interpretation in terms of identifying its interaction with ENSO via other SSTa outside of it) but I digress, is that by ONI we never achieved official Nina for 2024-2025 and 2025-2026, technically cold-neutral.

To have two solid Ninos in theory with two cold neutrals during a deep -PDO, odd indeed.

If we get another stout El Nino and the PDO remains negative then something is definitely broken. Even during -PDO regimes the PDO still manages to briefly flip positive when an El Nino forms.

[USTropics]

The only period where two fairly significant El Nino's I can see in the ONI index was 1963-1964 (moderate) and 1965-1966 (strong) that were relatively close to each other. It would be pretty rare to have two big ones so close. Even more odd (I know the RONI says differently; I still have debate if we are even using this index correctly/interpretation in terms of identifying its interaction with ENSO via other SSTa outside of it) but I digress, is that by ONI we never achieved official Nina for 2024-2025 and 2025-2026, technically cold-neutral.

To have two solid Ninos in theory with two cold neutrals during a deep -PDO, odd indeed.

If we get another stout El Nino and the PDO remains negative then something is definitely broken. Even during -PDO regimes the PDO still manages to briefly flip positive when an El Nino forms.

This is definitely interesting and something I've looked into recently. Similar to how revisionists will likely see our current state as La Nina when the new climatology period updates, there is some background GW signature not being accounted for here. It's important to also note -PDO doesn't determine El Nino generation, but does determine amplitude (particularly zonally). In other words, a strongly negative PDO modifies the Pacific mean state by enhancing the zonal SST gradient and steepening the thermocline tilt, favoring a more CPAC ENSO expression while suppressing EPAC cooling.

I think one of the important keys here is that La Nina does require stronger coupling than El Nino. This is why we can get super Ninos to begin with via WWBs, MJO propagation, Indo-Pacific Walker circulation shifts, and even Atlantic SST forcing (something I believe has really kicked into gear since the early 2000s and needs more research).

Some food for thought, are we seeing a more permanent thermocline tilt and a shift in ENSO-PDO covariance? That is, are we heading towards a future where the WPAC and CPAC become the dominant ENSO regions (instead of 3.4)? It's definitely to early/not enough data to quantify that, but the persistence of a negative PDO, while not indicating a breakdown of ENSO physics, is causing a 'decoupling' between ENSO dynamics and the SST pattern that project onto the current PDO index.

The main takeaway
Historically, El Nino often projects positively onto the PDO, but that's because PDO is heavily weighted toward EPAC SSTs. If El Nino expression becomes more CPAC/WPAC dominant (or zonally confined), the PDO may not flip even though ENSO discharge-recharge dynamics are active. Thus, this implies a shift in ENSO-PDO covariance (again, to early to confidently state that).

[Ntxw]

This is definitely interesting and something I've looked into recently. Similar to how revisionists will likely see our current state as La Nina when the new climatology period updates, there is some background GW signature not being accounted for here. It's important to also note -PDO doesn't determine El Nino generation, but does determine amplitude (particularly zonally). In other words, a strongly negative PDO modifies the Pacific mean state by enhancing the zonal SST gradient and steepening the thermocline tilt, favoring a more CPAC ENSO expression while suppressing EPAC cooling.

I think one of the important keys here is that La Nina does require stronger coupling than El Nino. This is why we can get super Ninos to begin with via WWBs, MJO propagation, Indo-Pacific Walker circulation shifts, and even Atlantic SST forcing (something I believe has really kicked into gear since the early 2000s and needs more research).

Some food for thought, are we seeing a more permanent thermocline tilt and a shift in ENSO-PDO covariance? That is, are we heading towards a future where the WPAC and CPAC become the dominant ENSO regions (instead of 3.4)? It's definitely to early/not enough data to quantify that, but the persistence of a negative PDO, while not indicating a breakdown of ENSO physics, is causing a 'decoupling' between ENSO dynamics and the SST pattern that project onto the current PDO index.

The main takeaway
Historically, El Nino often projects positively onto the PDO, but that's because PDO is heavily weighted toward EPAC SSTs. If El Nino expression becomes more CPAC/WPAC dominant (or zonally confined), the PDO may not flip even though ENSO discharge-recharge dynamics are active. Thus, this implies a shift in ENSO-PDO covariance (again, to early to confidently state that).

Something to consider, the extratropics is warming rapidly. Probably faster than the typical 30 year averages can keep up with. So the way PDO, AMO etc is considered it's all likely changed. What happens if the entire north Pacific or Atlantic is warm all the time and getting warmer? How do we differentiate it from a decadal cycle? The difference between one part of the basin to another is losing that gradient.

On another hand in the equatorial Pacific convection is effected, in an El Nino there is typically movement of the convection eastward due to warmer waters able to sustain it shifting eastward. What happens if the west remains well above normal and you have split forcing, continued MC convection despite not in a La Nina while the east is also warm enough to support it? What do we have? El nino? La Nina? La Nino? 2023 was a prime example of this type of split. We lost behaviors of the traditional strong Nino, but the ocean was clearly warm just like one but the atmosphere couldn't follow that tradition thus the RONI said otherwise. So to say the El Nino was weaker, I don't think is correct the ocean clearly noted that it was a strong event, the walker circulation just didn't flow the way we expected.

[Yellow Evan]

The only period where two fairly significant El Nino's I can see in the ONI index was 1963-1964 (moderate) and 1965-1966 (strong) that were relatively close to each other. It would be pretty rare to have two big ones so close. Even more odd (I know the RONI says differently; I still have debate if we are even using this index correctly/interpretation in terms of identifying its interaction with ENSO via other SSTa outside of it) but I digress, is that by ONI we never achieved official Nina for 2024-2025 and 2025-2026, technically cold-neutral.

To have two solid Ninos in theory with two cold neutrals during a deep -PDO, odd indeed.

If we get another stout El Nino and the PDO remains negative then something is definitely broken. Even during -PDO regimes the PDO still manages to briefly flip positive when an El Nino forms.

This is definitely interesting and something I've looked into recently. Similar to how revisionists will likely see our current state as La Nina when the new climatology period updates, there is some background GW signature not being accounted for here. It's important to also note -PDO doesn't determine El Nino generation, but does determine amplitude (particularly zonally). In other words, a strongly negative PDO modifies the Pacific mean state by enhancing the zonal SST gradient and steepening the thermocline tilt, favoring a more CPAC ENSO expression while suppressing EPAC cooling.

I think one of the important keys here is that La Nina does require stronger coupling than El Nino. This is why we can get super Ninos to begin with via WWBs, MJO propagation, Indo-Pacific Walker circulation shifts, and even Atlantic SST forcing (something I believe has really kicked into gear since the early 2000s and needs more research).

Some food for thought, are we seeing a more permanent thermocline tilt and a shift in ENSO-PDO covariance? That is, are we heading towards a future where the WPAC and CPAC become the dominant ENSO regions (instead of 3.4)? It's definitely to early/not enough data to quantify that, but the persistence of a negative PDO, while not indicating a breakdown of ENSO physics, is causing a 'decoupling' between ENSO dynamics and the SST pattern that project onto the current PDO index.

The main takeaway
Historically, El Nino often projects positively onto the PDO, but that's because PDO is heavily weighted toward EPAC SSTs. If El Nino expression becomes more CPAC/WPAC dominant (or zonally confined), the PDO may not flip even though ENSO discharge-recharge dynamics are active. Thus, this implies a shift in ENSO-PDO covariance (again, to early to confidently state that).

Traditionally, the PDO is defined as a EOF1 of NPAC SSTs but as time has gone on, the EOF2 (Victoria Mode) has become prominent (and appears to be present right now). See Ji. et al (2024) for more.

[USTropics]

This is definitely interesting and something I've looked into recently. Similar to how revisionists will likely see our current state as La Nina when the new climatology period updates, there is some background GW signature not being accounted for here. It's important to also note -PDO doesn't determine El Nino generation, but does determine amplitude (particularly zonally). In other words, a strongly negative PDO modifies the Pacific mean state by enhancing the zonal SST gradient and steepening the thermocline tilt, favoring a more CPAC ENSO expression while suppressing EPAC cooling.

I think one of the important keys here is that La Nina does require stronger coupling than El Nino. This is why we can get super Ninos to begin with via WWBs, MJO propagation, Indo-Pacific Walker circulation shifts, and even Atlantic SST forcing (something I believe has really kicked into gear since the early 2000s and needs more research).

Some food for thought, are we seeing a more permanent thermocline tilt and a shift in ENSO-PDO covariance? That is, are we heading towards a future where the WPAC and CPAC become the dominant ENSO regions (instead of 3.4)? It's definitely to early/not enough data to quantify that, but the persistence of a negative PDO, while not indicating a breakdown of ENSO physics, is causing a 'decoupling' between ENSO dynamics and the SST pattern that project onto the current PDO index.

The main takeaway
Historically, El Nino often projects positively onto the PDO, but that's because PDO is heavily weighted toward EPAC SSTs. If El Nino expression becomes more CPAC/WPAC dominant (or zonally confined), the PDO may not flip even though ENSO discharge-recharge dynamics are active. Thus, this implies a shift in ENSO-PDO covariance (again, to early to confidently state that).

Something to consider, the extratropics is warming rapidly. Probably faster than the typical 30 year averages can keep up with. So the way PDO, AMO etc is considered it's all likely changed. What happens if the entire north Pacific or Atlantic is warm all the time and getting warmer? How do we differentiate it from a decadal cycle? The difference between one part of the basin to another is losing that gradient.

On another hand in the equatorial Pacific convection is effected, in an El Nino there is typically movement of the convection eastward due to warmer waters able to sustain it shifting eastward. What happens if the west remains well above normal and you have split forcing, continued MC convection despite not in a La Nina while the east is also warm enough to support it? What do we have? El nino? La Nina? La Nino? 2023 was a prime example of this type of split. We lost behaviors of the traditional strong Nino, but the ocean was clearly warm just like one but the atmosphere couldn't follow that tradition thus the RONI said otherwise. So to say the El Nino was weaker, I don't think is correct the ocean clearly noted that it was a strong event, the walker circulation just didn't flow the way we expected.

If we get another stout El Nino and the PDO remains negative then something is definitely broken. Even during -PDO regimes the PDO still manages to briefly flip positive when an El Nino forms.

This is definitely interesting and something I've looked into recently. Similar to how revisionists will likely see our current state as La Nina when the new climatology period updates, there is some background GW signature not being accounted for here. It's important to also note -PDO doesn't determine El Nino generation, but does determine amplitude (particularly zonally). In other words, a strongly negative PDO modifies the Pacific mean state by enhancing the zonal SST gradient and steepening the thermocline tilt, favoring a more CPAC ENSO expression while suppressing EPAC cooling.

I think one of the important keys here is that La Nina does require stronger coupling than El Nino. This is why we can get super Ninos to begin with via WWBs, MJO propagation, Indo-Pacific Walker circulation shifts, and even Atlantic SST forcing (something I believe has really kicked into gear since the early 2000s and needs more research).

Some food for thought, are we seeing a more permanent thermocline tilt and a shift in ENSO-PDO covariance? That is, are we heading towards a future where the WPAC and CPAC become the dominant ENSO regions (instead of 3.4)? It's definitely to early/not enough data to quantify that, but the persistence of a negative PDO, while not indicating a breakdown of ENSO physics, is causing a 'decoupling' between ENSO dynamics and the SST pattern that project onto the current PDO index.

The main takeaway
Historically, El Nino often projects positively onto the PDO, but that's because PDO is heavily weighted toward EPAC SSTs. If El Nino expression becomes more CPAC/WPAC dominant (or zonally confined), the PDO may not flip even though ENSO discharge-recharge dynamics are active. Thus, this implies a shift in ENSO-PDO covariance (again, to early to confidently state that).

Traditionally, the PDO is defined as a EOF1 of NPAC SSTs but as time has gone on, the EOF2 (Victoria Mode) has become prominent (and appears to be present right now). See Ji. et al (2024) for more.

I'll respond to both these posts because I think they go hand in hand.

First, thanks for sharing this article and noting these EOF modes! Actually have not seen this article yet and will dive in deeper on the methods later, but the discussion definitely highlights some of my suspicions.

• PDO variability significantly declined around ~1990-2000
• GW + increased ocean stratification at the surface reduces some of this coupling (thus alters thermocline)
• CPAC becomes more of the dominant driver/feature of ENSO events now

Ntxw makes some really important points here, and I think it actually reinforces the idea that our traditional indices are struggling to separate structure from background state due to rather rapid changes (where 30 year climatology periods can't even keep up). No doubt, the poles are warming significantly faster than the equator, and this inherently complicates traditional PDO (and even AMV imo) as true decadal modes versus evolving mean-state patterns. That is, the SST/ONI pattern screams El Nino, but our traditional atmospheric/oceanic connections have been altered.

Another important aspect to look at is the latitudinal gradient SST shift and how this allows the ITCZ to move further north (i.e., convection can sustain further north).

So do we think this is just more variability, or do we have to eventually redefine ENSO ocean-atmospheric coupling signals? Do CPAC SSTs allow for convection to still dominate there, despite other region's SST variability?

My assumptions are we've permanently altered SST/convection gradients and the thermocline -> enhances CPAC ability to generate convection -> this shifts ITCZ position -> Walker circulation shifts and traditional ocean-atmospheric ENSO coupling is altered.

[cycloneye]

The WWB continues to look impressive.

[cycloneye]

 https://x.com/PaulRoundy1/status/2009412354539241561

[Teban54]

You know that an El Nino is expected when the ENSO thread is buzzing 8 days into the new year.

[cycloneye]

You know that an El Nino is expected when the ENSO thread is buzzing 8 days into the new year.

That is why started the thread, more earlier than usual, on november 10th, as I knew this was going to be the most busy one, more than the indicators thread as the buzz around the net has been about the development of El Niño.

[cycloneye]

I encourage the members to read the whole article. Link below.

https://www.severe-weather.eu/long-rang ... europe-fa/

 https://x.com/severeweatherEU/status/2009526090709000375