2025 ENSO/Winter Speculation

[40/70 Benchmark]

On 9/20/2025 at 11:53 AM, weathafella said:

I think this validates what I said-no longer east based but more basin wide and weak.  Probably will be less of a factor in terms of predictability of the season this year.

No; it invalidates it. The eastern zone of 1.2 began warm and the subsurface cold pool emerged there.

[40/70 Benchmark]

On 9/19/2025 at 1:51 PM, weatherwiz said:

Also keep in mind 1.2 is the most volatile region so when assessing changes in SST structure you must factor in what the contributions are to that.

Yes, I think Jerry is focusing on region 3...while 1.2 is volatile....this marked cooling in that zone isn't a function of volatility. If you have been paying attention, the subsurface cold pool emerged due to sustained trades.

[40/70 Benchmark]

Also, if you look at guidance, this has been expected and well forecast.

 

[40/70 Benchmark]

Now, maybe these trends reverse and guidance will be wrong, but that is not what we are seeing now. It's not becoming less east-based.

[40/70 Benchmark]

Region 1.2 has warmed again, speakaing to the volatility that Paul mentioned, but the subsurface remains supportive of an east-biased event.

[H2Otown_WX]

12 hours ago, 40/70 Benchmark said:

Region 1.2 has warmed again, speakaing to the volatility that Paul mentioned, but the subsurface remains supportive of an east-biased event.

Any chance of a weak west based Modoki Nino? 

[40/70 Benchmark]

 

Guidance Aligning with Eastern Mass Weather Expectation for Weak La Niña

Confidence in ENSO Analogs Growing

September ENSO Update

The updated consensus from the International Research Institute (IRI) for the month of September has finally reflected the significant cooling trend that Eastern Mass Weather has been advertising since the month of July. Indeed, after supporting an ENSO neutral peak that was warmer than the La Niña threshold (-0.5C) in region 3.4 all throughout this past summer, anywhere between -.31C and -.42C, the September suite now matches the preliminary Eastern Mass Weather forecast within a peak range of between -0.5C and -0.7C.

 

When viewing the latest subsurface data, it is easy to see why this latest suite of guidance finally followed the relatively aggressive trend towards cool ENSO that had been anticipated. Note the recent burst of easterly trades during much of the month of August in the annotation below, which triggered the upwelling of the rather extensive subsurface cold pool over the eastern half of the ENSO regions to the surface.

 

 

 

The ramifications of this expected development are two-fold. Firstly, the notion of this particular cool ENSO event meeting the technical definition of La Niña per CPC cannot yet entirely be discounted. While the concept of an official La Niña designation remains dubious considering the next round of trades is expected to be weaker, they had been relatively impressive throughout the summer, and were even prevalent enough to compare favorably to those that normally precede the development of weak La Niña.

 

Additionally, the pressure dipole, which consists of lower pressure across the western Pacific and higher pressures to the east in a developing cool ENSO event, has also been slightly more impressive than the weak La Niña group.

 

 

This is unsurprising considering that the MJJA mean SOI value for 2025 is 2.96, which is actually slightly higher (more La Niña like) than the weak La Nina composite MJJA value of 2.71. What is being observed is a continuation of the predominate trend of the past decade for the atmosphere to be more representative of La Niña than the ONI would imply due to the western Pacific warm pool.

 

Warmer West/Cooler East Pacific SST Anomaly Dipole Characteristic of Cool ENSO

 

  This is why the Relative Ocean Nino Index (RONI), which in a simplistic sense de-trends the general background warming of the tropics that is attributed to climate change from ENSO, is of greater importance. The current tri-monthly JJA RONI value of -.46 is already bordering on La Niña territory, and is likely to finish anywhere between. -0.9 and -1.1 based on analog seasons. The continued descent of both the IOD (left) and the AAM (right) is also reflective of an atmosphere that is entering La Niña mode more aggressively than the ONI would imply, and thus rendering an official designation per ONI, which is still considered unlikely due to the fairly late start of the more concerted cooling, moot. 

 

 

 

The second consequence of the stronger interval of easterly trades triggering the surfacing of the subsurface cold pool in the eastern half of the ENSO region is that it reaffirms the idea that this particular cool ENSO event will remain at least somewhat eastern biased throughout the fall and into boreal winter season. 

Expectation for Eastern-Biased Cool ENSO Remains

The rapid cooling recorded in the Eastern region of 1.2 from 0.8C above average on August 6th to -0.3 below average by August 27 is very evident in the CPC data below.

 

    Date              1.2       3        3.4      4

        

06AUG2025      0.8     -0.1     -0.3     0.0

 13AUG2025      0.6     0.0     -0.3     0.1

 20AUG2025     -0.1     -0.3     -0.4    -0.1

 27AUG2025     -0.3     -0.6     -0.4     -0.2

 03SEP2025     -0.2     -0.4     0.3     -0.2

 10SEP2025     -0.2     -0.5     -0.5     -0.3

 17SEP2025    0.0     -0.4     -0.4    -0.3

 

Note that although this was followed by a slight recovery with the abatement and translation westward of the trades in September, the event currently remains consistent with the east-based composite in which the max anomalies are centered between about 120 and 140 degrees longitude.

Current SST Profile Matches East-Based Composite (Max Anomaly 120-140W)

East-Based La Niña Composite (Max Anomaly 120W)

The persistence of this regime is generally supported by the consensus of guidance, which is perhaps slightly more supportive of an eastward leaning basin-wide event by winter, as opposed to a bonafide east-base event. This is perceived to be a rather trivial discrepancy, especially given the modest strength of the ENSO event.

 

 

The newest El Niño Modoki Index (EMI) guidance from JAMSTEC has also remained fairly consisted in it's depiction of an EMI value of around -.20 to -.30 during the boreal winter season.

 

 

This range is similar to the EMI analogs of 1995-1996, 2017-2018 and 2021-2022, which is supported by the similarity in both the placement (near 140 longitude) and the intensity of the respective subsurface cold pool analogs relative to 2025.

 

 

One final point of interest in closing is that the only slight change from the EMI August guidance is that it delayed the onset of the eastward translation, presumably owed to the fact that it took until latter August for the subsurface cold pool to surface in region 1.2. This will be a trend to watch moving though the fall in the event that the recent cooling in region 1.2 becomes a trend; however, this particular region is prone to volatility and the subsurface is currently not conducive to any such trend.

 

Now that enough information has been gleaned throughout the summer and into the onset of boreal autumn, a preliminary seasonal composite can be introduced.

Preliminary DJFM Seasonal 500mb/Temperature Anomaly Composite

The operative word here is "preliminary", as this these forecast products will be subject to changes over the course of the next six weeks, prior to the issuance of the final products in November. That being said, without further ado:

 

DJFM 2025-2026 Per 1991-2020 Climate Period

The above composite is the product of an integration of polar, extra tropical Pacific, ENSO and summer-fall temperature analogs.

One final ENSO update will be issued in latter October before the complete Winter Outlook 2025-2026 is published in November.

 

[dryslot]

The 3 driest summers here in Maine are/were 2025, 1995 and 1968, Winter 68-69 for PWM, 110" of snow, 95-96, 123".

[40/70 Benchmark]

37 minutes ago, dryslot said:

The 3 driest summers here in Maine are/were 2025, 1995 and 1968, Winter 68-69 for PWM, 110" of snow, 95-96, 123".

I don't exactly "hate" the 1970 and 2007 analogs, either. 

[dryslot]

7 minutes ago, 40/70 Benchmark said:

I don't exactly "hate" the 1970 and 2007 analogs, either. 

I don't either, 144" and 138" ha ha.

[TheMainer]

7 hours ago, dryslot said:

The 3 driest summers here in Maine are/were 2025, 1995 and 1968, Winter 68-69 for PWM, 110" of snow, 95-96, 123".

Correlation does not equal causation, but in this case I hope it does! We need a good snowmobile registration year or we're going to start having some serious trail funding issues. I had to beg and plead for the state to give us 50% of what we need for a major reroute due to an out of stater buying land and shutting off a snowmobile trail used since 1972...

 

[40/70 Benchmark]

8 hours ago, dryslot said:

I don't either, 144" and 138" ha ha.

I probably had like 80" those seasons....sign me up.

[40/70 Benchmark]

2 hours ago, 40/70 Benchmark said:

Interesting...a bit of overlap...1993 common denominator. I looked at that season, but ultimately disregarded because there was too much of a warm ENSO flavor to it.

@weathafella

[MJO812]

Snowing in Alaska

[Snowcrazed71]

So... There were similarities from the Summer of 1995 to this past Summer of 2025 ( although there was was a very small area of Tolland and Windham county that experienced above normal precipitation in July ). And we all know what happened in the winter of 1995/1996.... I'm not saying that's going to happen this winter, but, there were similarities

 

( During the summer of 2025 (June–August), Bridgeport, Connecticut, had its driest summer on record since 1948. The city recorded only 3.85 inches of rain during the entire season, surpassing the previous record of 4.13 inches set in 1995 )

 

During the summer of 1995, the Northeast experienced a severe drought and a notable heat wave in July, with August being especially dry. Overall, the season was significantly drier and warmer than normal, though regional variations occurred. 

Temperature

A major heat wave in July was the most defining temperature event of the summer. 

• Regional heat wave: Excessive heat and humidity spread into the northeastern United States by mid-July, after affecting the Great Plains and Midwest.
• Peak heat: The heat peaked around July 14, with temperatures in the 95–100°F range for some areas. The combination of heat and high humidity led to exceptionally high heat indices, exceeding 115°F in some locations.
• Persistent high temperatures: Some parts of the region experienced stretches of temperatures at or above 90°F during both June and August, in addition to the July heat wave. For example, locations from Philadelphia to Richmond saw 90+°F temperatures on 40 to 44 days during the summer.
• Above-normal averages: The average temperature for the summer was above normal for many areas, though not always drastically so. For instance, the Hartford, Connecticut, area had an average temperature of 72.2°F, which was just 0.3°F above normal. 

Precipitation

A persistent and expanding drought was the key precipitation story of the summer, with August being exceptionally dry. 

• Overall precipitation: The Northeast received 9.94 inches of precipitation, which was only 78% of the normal amount, making it the 19th-driest summer on record.
• Record dryness: Drought conditions intensified throughout the season, becoming moderate to severe by August. Many states experienced one of their driest summers or driest Augusts on record.
  • Driest summer: New Hampshire had its driest summer on record, while Vermont had its second-driest.
  • Driest August: Washington, D.C. experienced its driest August since 1871, receiving only 0.20 inches of rain. Vermont also had its driest August on record.
• Regional impact: The drought's intensity varied. For example, Bridgeport, Connecticut, recorded its driest summer on record with just 4.13 inches of rain. However, the nearby Hartford area was closer to normal for the season.
• August rainfall deficits: August precipitation was particularly low across the region, with significant rainfall deficits reported in nearly all states. 

[40/70 Benchmark]

9 hours ago, Snowcrazed71 said:

So... There were similarities from the Summer of 1995 to this past Summer of 2025 ( although there was was a very small area of Tolland and Windham county that experienced above normal precipitation in July ). And we all know what happened in the winter of 1995/1996.... I'm not saying that's going to happen this winter, but, there were similarities

 

( During the summer of 2025 (June–August), Bridgeport, Connecticut, had its driest summer on record since 1948. The city recorded only 3.85 inches of rain during the entire season, surpassing the previous record of 4.13 inches set in 1995 )

 

During the summer of 1995, the Northeast experienced a severe drought and a notable heat wave in July, with August being especially dry. Overall, the season was significantly drier and warmer than normal, though regional variations occurred. 

Temperature

A major heat wave in July was the most defining temperature event of the summer. 

• Regional heat wave: Excessive heat and humidity spread into the northeastern United States by mid-July, after affecting the Great Plains and Midwest.
• Peak heat: The heat peaked around July 14, with temperatures in the 95–100°F range for some areas. The combination of heat and high humidity led to exceptionally high heat indices, exceeding 115°F in some locations.
• Persistent high temperatures: Some parts of the region experienced stretches of temperatures at or above 90°F during both June and August, in addition to the July heat wave. For example, locations from Philadelphia to Richmond saw 90+°F temperatures on 40 to 44 days during the summer.
• Above-normal averages: The average temperature for the summer was above normal for many areas, though not always drastically so. For instance, the Hartford, Connecticut, area had an average temperature of 72.2°F, which was just 0.3°F above normal. 

Precipitation

A persistent and expanding drought was the key precipitation story of the summer, with August being exceptionally dry. 

• Overall precipitation: The Northeast received 9.94 inches of precipitation, which was only 78% of the normal amount, making it the 19th-driest summer on record.
• Record dryness: Drought conditions intensified throughout the season, becoming moderate to severe by August. Many states experienced one of their driest summers or driest Augusts on record.
  • Driest summer: New Hampshire had its driest summer on record, while Vermont had its second-driest.
  • Driest August: Washington, D.C. experienced its driest August since 1871, receiving only 0.20 inches of rain. Vermont also had its driest August on record.
• Regional impact: The drought's intensity varied. For example, Bridgeport, Connecticut, recorded its driest summer on record with just 4.13 inches of rain. However, the nearby Hartford area was closer to normal for the season.
• August rainfall deficits: August precipitation was particularly low across the region, with significant rainfall deficits reported in nearly all states. 

Yea, obviously the point isn't to expect a record winter, but rather we shouldn't be resigned to another dud because the year has been dry thus far.

[WxWatcher007]

1 hour ago, 40/70 Benchmark said:

Yea, obviously the point isn't to expect a record winter, but rather we shouldn't be resigned to another dud because the year has been dry thus far.

I hope so. I haven’t done too much thinking about winter yet but it’s less that it’s been dry thus far in my mind and more the background state of warm seasons and worse, that it seems our results are untethered from patterns that normally would be good to great for us. That concerns me. Like @CoastalWx, I’ve totally lost faith after the last decade. 

 

[40/70 Benchmark]

21 minutes ago, WxWatcher007 said:

I hope so. I haven’t done too much thinking about winter yet but it’s less that it’s been dry thus far in my mind and more the background state of warm seasons and worse, that it seems our results are untethered from patterns that normally would be good to great for us. That concerns me. Like @CoastalWx, I’ve totally lost faith after the last decade. 

 

Yes and no....I agree generally with what you are saying, but it's not the warming itself that is prohibitive to having good seasons....it's the western warm pool in-and-of-itself that is the reason NAO blocking hasn't been paying dividends....AKA +WPO. Do me a favor and find a great SNE season that also had a strongly +WPO......you can't find one...not in 1948, and not in 2025.

https://psl.noaa.gov/data/correlation/wp.data

Extreme +WPO being prohibitive isn't a recent development, but rather the consistency and strength of it is. Since 2016-2017, 2021-2022 is the only -WPO season we have had......the concern is that this is some sort of permanent pattern as a result of CC. While we won't know definitely for another 10 years or so, I am still of the opinion that the globe will find a way to achieve balance, and will wait before seeing otherwise.

As for the WPO....we here in SNE can thrive with a modestly +WPO value, as was the case in 2017-2018....and yes, we can still get a -WPO season, as was the case in 2021-2022. That being said, SSTs over the eastern Indian ocean do look supportive of +WPO, but the hope is that more abundant E PAC warmth can counter that in much the same manner that the West warm Pool did with El Nino a couple of seasons back...think Relative Ocean Nino Index https://www.cpc.ncep.noaa.gov/data/indices/RONI.ascii.txt

Always remeber that NOTHING operates in a vacuum, so don't obsess too over any single point on the globe, as ultimately it is not what is going on at said point that is paramount, but rather what is going on at said point relative to the rest of the globe.

[Typhoon Tip]

2 hours ago, 40/70 Benchmark said:

Yes and no....I agree generally with what you are saying, but it's not the warming itself that is prohibitive to having good seasons....it's the western warm pool in-and-of-itself that is the reason NAO blocking hasn't been paying dividends....AKA +WPO. Do me a favor and find a great SNE season that also had a strongly +WPO......you can't find one...not in 1948, and not in 2025.

https://psl.noaa.gov/data/correlation/wp.data

Extreme +WPO being prohibitive isn't a recent development, but rather the consistency and strength of it is. Since 2016-2017, 2021-2022 is the only -WPO season we have had......the concern is that this is some sort of permanent pattern as a result of CC. While we won't know definitely for another 10 years or so, I am still of the opinion that the globe will find a way to achieve balance, and will wait before seeing otherwise.

As for the WPO....we here in SNE can thrive with a modestly +WPO value, as was the case in 2017-2018....and yes, we can still get a -WPO season, as was the case in 2021-2022. That being said, SSTs over the eastern Indian ocean do look supportive of +WPO, but the hope is that more abundant E PAC warmth can counter that in much the same manner that the West warm Pool did with El Nino a couple of seasons back...think Relative Ocean Nino Index https://www.cpc.ncep.noaa.gov/data/indices/RONI.ascii.txt

Always remeber that NOTHING operates in a vacuum, so don't obsess too over any single point on the globe, as ultimately it is not what is going on at said point that is paramount, but rather what is going on at said point relative to the rest of the globe.

I'd add to this discussion that these indices are also increasingly non-resonant.   Meaning, they are less (apparently...) physically forced into a quasi-stable mode. 

The reason for that is related to the increased winter time gradient in the whole sale integral of the subtropical to Ferril latitude band.  Faster basal flow velocities sends the Roulette wheel spinning more frequently - metaphor.

[40/70 Benchmark]

1 hour ago, Typhoon Tip said:

I'd add to this discussion that these indices are also increasingly non-resonant.   Meaning, they are less (apparently...) physically forced into a quasi-stable mode. 

The reason for that is related to the increased winter time gradient in the whole sale integral of the subtropical to Ferril latitude band.  Faster basal flow velocities sends the Roulette wheel spinning more frequently - metaphor.

I think part of this, not all, is due to the ++WPO that we have had the last decade.