40/70 Benchmark

I went back and edited to give the IOD and AAM a shoutout just for snowman.

@snowman19Lowest I see in 2008 is -.128 in November 2008...we have had much lower since then....not sure why you are saying this is the lowest since then? November 2010 was -.495. Edit, oh Aussie....this data is different. https://psl.noaa.gov/gcos_wgsp/Timeseries/Data/dmi.had.long.data I find it hard to believe that 2010 wasn't a more negative IOD.

Which harkens back to my point....I have a hard time believing this event cools less than 1967 did the rest of the way, which is what you are implying. The trades are stronger, the subsurface is cooler, the SOI is higher and the IOD more conducive....but we'll see. I would expect a bit less cooling than 2008 featured from this point on.

Pretty confident you're gonna need a bigger boat. Anyway, these oscillations happened over the summer, as well....it recovered. Additionally, 2008 was not only the last year with this type of warm pool in the western subsurface, but also the last IOD that was this well defined. Coincidence?? It's probably at least somewhat of a protective factor against a premature demise. Anyone know what the IOD was like in 1967?

This is why I only care about snow.

Yea, I personally don't see it as a big deal, but it certainly doesn't hurt the case for an official La Niña designation.

Yea, the healthy -IOD bolsters the case for not jumping ship due to the subsurface...I didn't get into the IOD and GLAAM here because it was just a brief updated synopsis, but I definitely will in the seasonal analysis.

Final ENSO update prior to go-time second week of Novie. https://easternmassweather.blogspot.com/2025/10/official-la-nina-now-appears-likely-for.html

Last update from me prior to go-time. Confidence is high. Official La Niña Now Appears Likely for Winter '25-26' Subsurface Yields Invaluable Clues October IRI Update There have been no major changes to the October suite of the International Research Institute (IRI) ENSO guidance. In fact, the consensus seems to be coming into exceptionally good agreement, as the dynamical guidance has warmed ever so slightly, and the statistical guidance cooled with both settling in around a peak of about -0.6C. While intensity guidance has remained rather consistent, there have been a couple notable changes both with respect to the surface and the subsurface of the equatorial Pacific. Recent ENSO Developments During the month of September, Eastern Mass Weather anticipated that another round of trades near the close of the month and into the month of October would trigger significant cooling over the eastern half of the ENSO regions. This is indeed evident in the recent data. 1.2 3 3.4 4 17SEP2025 -0.0 -0.4 -0.4 -0.3 24SEP2025 -0.1 -0.4 -0.5 -0.3 01OCT2025 -0.1 -0.3 -0.5 -0.4 08OCT2025 -0.1 -0.1 -0.3 -0.3 15OCT2025 -0.4 -0.5 -0.6 -0.2 Note the drop from 0.0 in region 1.2 on September 17, to -0.4 as of October 15th, which has reenforced the east-based configuration. This cooling will slow or even halt over the next week, before resuming near the end of the month and culminating in a likely peak of the weeklies during the month of November. What is also evident is not only the lack of cooling in the western flank of region 4, but in fact slight warming, from -0.3 to -0.2. This is the result of the second noteworthy trend in that a considerable subsurface warm pool has been working into the western half of region 3.4 to the west of 150W. The ramifications of this are twofold; firstly, it is now a virtual certainty that this event will indeed remain eastern biased, which has been the supposition all summer and into the fall. The primary El Niño Modoki analogs have and will remain 1995, 2017 and 2021. In fact, the subsurface bias to the east in 2025 is even more drastic than it was in all 3 primary EMI analog years. The second implication of this is that there is a limit to just how potent La Niña can grow given that the end is in sight, but perhaps not as restrictive as one may perceive. Western Subsurface Warmth is Telling The logical assumption is that the encroachment of the subsurface warm pool into the western flank of the developing La Niña will limit it's additional growth, thus confirming the climatology based assertion made by Eastern Mass Weather in July, that this event would not achieve official La Niña status as designated by the Climate Prediction Center (CPC). However, when considering the degree of cooling that has already occurred over region 3.4 in conjunction with two notable past instances of developing western subsurface warmth, it is now clear that this is a position worth reconsidering. There are two evident analogs when considering this development and they are the years 1967 and 2008, respectively, the latter of which also represented a very good analog for the late development of cool ENSO event that occurred last season. The similarities in the subsurface are clear: The July-August-September 90 day SOI are as follows, from most favorable to least favorable for development of La Niña: 2008: 23.92 2025: 8.64 1967: 5.8 The trade winds were as one would expect given the respective 90 day SOI values, as 2008 features the strongest trades and 1967 the weakest by far. When considering all of the above data, 2008 was best poised for further cooling of La Nina and 1967, which failed to be officially designated, the least. The current cool ENSO event of 2025 is much more comparable to 2008 not only in terms of the formidable trades and positive SOI, but also given the ongoing considerable -IOD, which serves as a protective factor in relation to any potential premature decay of La Niña. Thus given that the ONI in 2008 dropped another 0.6 from the JAS value of -0.2, and 1967 another 0.5 from the JAS value of -0.2, it is prudent to anticipate a peak in 2025 in the -0.7 to -0.9 range when considering the current JAS value of -0.3, despite the considerable incursion of subsurface warmth lurking to the west. This update to the anticipated peak ONI range of -0.7 to -0.9 is crucial because since 1950, the only event to reach an ONI value of -0.7 and not go on to be officially designated a La Niña is......1967, which as previously illustrated, occurred during a season in which the hemisphere was not as conducive to it's development as it is in 2025. Applying the expected rate of growth of the current JAS RONI value of -0.63 yields a peak value in the -1 to -1.2 range, which is congruent with the forecast bottoming out of the hemispheric angular momentum as the event reaches a weekly peak in November. Thus it appears that the atmosphere will indeed be rather well coupled with the maturing cool ENSO event, and the recent issuance of the La Niña Advisory by the CPC on October 9th was indeed warranted. The advancement of subsurface warmth is not necessarily prohibitive. It is also important to remain mindful that an even more pronounced expansion of subsurface warmth took place over the summer, when the vast majority of the ENSO subsurface had warmed considerably only to recover in August. Furthermore, although the event is expected to evolve into an east-based fashion, the latest Jamstec guidance does imply a brief pullback into a more central-based, or basin-wide configuration given the forecast brief spike in the EMI value during the month of November. This is feasible given the anticipated lull in the cooling over the eastern region owed to the brief relaxation of the trades during the coming week, in conjunction with a potential reemergence of a cool eddy in the subsurface of region 4 amid the continued presence of ample trades. While it is unlikely that the developing warm pool over the western half of ENSO will recede as much as did during the month of August, it does in fact serve as a reminder of the capricious nature of the subsurface. Winter Outlook 2025-2026 will be the next publication during the second week of November-

Take a look at July...it was much worse. Warm subsurface all beneath region 3.4.

Looking at this more, the subsurface has been beaten back in region 3.4 relative to where it was in September, but it's really a push from August....looks very similar to August. I don't think a collapse is imminent, but like I said...this does seem to validate JAMESTEC maintaining and east based event. I have been touting 2021-2022, 2017-2018 and 1995-1996 as EMI analogs since early last summer. This subsurface look is about according to plan if you ask me.

I agree RE the slight shift west, but stronger La Niña and weaker indo-Pacific warm pool relative to what?

That looks pretty realistic.

Tricky part for me is I not only forecast the sensible weather, but the actual teleconnections, so this may matter to me more than most. Anyway, look forward to what you present.

I think the course of least regret is incorporating La Niña analogs, but emphasizing variability with respect to the PNA....including some +PNA cool ENSO analogs, as well...such as 2024 and 2000, which are both stellar polar analogs.