GaWx

Based on past instances following a sustained strong SOI drop like we've had and which will last a couple more days before rising substantially making it a 17 day solid -SOI, the weekly 3.4 SST anomalies would often rise a few tenths ~3-4 weeks afterward. In this case, that would mean early to mid June. As of last week, 3.4 was still at +0.5. Let's see whether or not there's a rise to +0.8 or so by mid June. Keeping in mind what you said about this case differing quite a bit from other sub -9 Mays, I realize that the typical reaction in Nino 3.4 may not occur. It will be interesting to follow!

The volatile weekly Nino 1+2 region SST anomaly just released (for last week) dropped pretty sharply from +2.4 to +1.7, the coolest in two months. The other three regions changed little or none. The daily SOI plunged to -43. It will be even lower tomorrow, which should be the low point of the month.

But today he posted like the traditional JB as a result of a cool 6Z CFSv2 run for DJF resulting largely from a strong -NAO:

Regardless, the correlation between a sub -9 May SOI and whether or not an oncoming Nino actually occurs has been pretty strong. Since 1950, there have been 14 sub -9 Mays. The only ones not followed by El Niño were the -11.7 of 2005 (that was attributed to lingering effects of the 2004-5 Nino) and the -9.9 of 2001. So, 2001 is the only one of the 14 without explanation. Is there a website to follow the daily EOI? Also, I'd like to see historical EOI data to analyze that is comparable to the SOI historical data that goes way back into the mid 1800s. Are there specific locations' SLPs that determine the EOI like Tahiti and Darwin of the SOI?

Though far from perfect, I've found based on looking at many years of SOI/SST anomaly data that monthly SOI drops are often a pretty good 30-60 day leading indicator for Nino 3.4 SST anomaly rises. So, with a solidly -SOI in May, I'll be looking to see if there's a significant 3.4 anomaly rise in June-July.

SOI monthlies in 2014: After an early solid -SOI in Mar and an accompanying notable Nino 3.4 SST anomaly rise in early spring, Apr-Jul SOIs were ~neutral and SST anomalies became steady. Then -SOI finally came back solidly Aug-Dec, which coincided well with SST anomalies finally rising Sep onward: Jan +11 Feb -2 Mar -12 Apr +6 May +4 Jun -1 Jul -4 Aug -10 Sep -7 Oct-Dec -8 2015: -SOIs dominated entire year with 3 month largest dip (Aug-Oct) way down at -19. SOI didn't rise to neutral til May of 2016, when SST anomalies finally rose to neutral.

Today's SOI came in at ~-26. I'm very roughly estimating the next four days to come in at -35, -57 (lowest daily since 2/6/2010), -50, and -33 followed by a rapid rise. We appear to be looking at ~-12 for May as a whole, a solid indicator for an upcoming Nino of difficult to predict magnitude.

Based on the site noted below, the last two days have been the coldest on record for the date (back to 1958) in the Arctic (80-90N) at 4-5 C BN, which is just colder than 2015, 1962, and 1964. https://ocean.dmi.dk/arctic/meant80n.uk.php The AO has been way up at +2.6 to +2.7 the last two days, the highest on record for the period (since 1950).

On May 10, @bluewaveposted this: "I know that these seasonal forecasts aren’t great. But they are forecasting the -PDO to weaken a bit in the coming months. This would be expected if some of the stronger forecasts for the El Niño worked out." I responded to his post with this: "That's quite a rise forecasted for the PDO between April and July with still another 5 months to go even after that before winter starts. That suggests that a rise to low -1s is quite possible in July. That wouldn't be all that far from +0.50 being that there'd be five months to go." So, being that the recent PDO rise was forecasted, this is following model forecasts thus far. I'm keeping these three past cases of very sharp PDO rises during a new Nino in mind, which tell me there's a small chance that the upcoming DJF PDO will exceed +0.5: 1. Nov-Apr 1883-4 was -1.4. DJF of the very cold 1884-5 was way up at +1.98. That's a 3.38 rise! 2. Nov-Apr of 1975-6 was -1.9. DJF of 1976-7 was up at +1.32. That's a rise of 3.22! 3. Nov-Apr of 2001-2 was -1.3. DJF of 2002-3 was up at +1.42 for a rise of 2.72!

Interesting! Could this be indirectly related to the cold bias of most models in the E US, especially in winter, that results from underestimation of the southeast ridge that has been cited by some pro mets as being largely due to the underestimation of tropical forcing from the near record warm Maritime Continent/W Pacific? I've learned about the idea that record warmth in the MC often makes the atmosphere in the US act as if the MJO is in the MC phases even when it isn't officially in addition to lengthening and strengthening actual MC phases. So with MC MJO phases tending to favor an SER, the models underestimating the forcing from the MC means underestimating the SER. This appears to be the main reason why it is underestimated though the underestimate of the blocking from the near record +AMO is likely an additional factor. Between these two factors, the SER is strongly underestimated, which often results in a NW shift in storm tracks and other features as model forecast time gets closer and closer. So if anyone ever wondered why modeled storm tracks so often shift NW, this appears to be the explanation. So, back to my original question to Bluewave, @jconsorand others. Is what they're talking about here related at all to the same underestimate of MC/W Pac forcing from record warmth that causes the SER to be undermodeled?

Thanks. Per ONI I still favor a strong fall/winter peak but with high end moderate (+1.3 to +1.4) on the low side and super (+2.0+) on the high side. That puts me +1.6 to +1.9 for most likely. But per RONI assuming a -0.4 adjustment due to very warm overall tropical SSTAs, anywhere from a high end weak (+0.9) to low end super (near +2.0) is reasonably possible for the fall/winter peak with +1.2 to +1.5 for most likely. ------------ Redifining Nino indices in a warming climate (relates to RONI): https://iopscience.iop.org/article/10.1088/1748-9326/abe9ed/pdf

Followup: Today's SOI did rise but only barely/much less than I thought with it still down at -9.48. That now tells me that the -SOI streak is safe to continue for a good number more days with it now at 11 days. It should end up at 17+ days as it looks now. Due to the combo of way above normal Darwin and significantly below normal Tahiti SLP, the GFS and Euro are suggesting a sub -50 SOI is quite possible on May 23rd. That would mean the lowest daily SOI since at least the -52 of 2/17/2017 and possibly the lowest since the -58 of 2/6/2010! It would also mean the lowest daily May SOI since 1997. May MTD is now at -8.3. With this very strong -SOI period coming next week, a sub -10 May of 2023 is now just about a certainty. That is a very strong indicator of an upcoming El Niño of an unknown magnitude.

Followup: Today's SOI of -9.86 is the 10th -SOI in a row and brings down the MTD to -8. The SOI will rise tomorrow and it will be a close call as to whether or not we get the 11th -SOI in this streak. If we end up with -SOIs the next two days, the streak would very likely go a good number of days longer thanks to low Tahiti SLP with a small chance it could even go through the end of the month. The chance for a sub -10 for May, overall, continues to increase. Since 1950, there have been 11 sub -10 May SOIs. Only one of those 11 Mays didn't precede a new El Niño that autumn/winter. That was 2005. The reason May of 2005 was sub -10 was that the preceding Nino of 2004-5 was still lingering into April and May in the atmosphere, which sometimes happens.

The MTD SOI continues to drop and is now down to -7 after eight days in a row of sub -10. That's the first time for that long of a sub -10 streak since Sept of 2019. The next seven days' SLPs at Darwin are forecasted to remain well above normal with a short term peak ~5/22. Also, Tahiti is starting from ~5/21 forecasted to have BN SLP for most of the rest of the month with some days MB. So, bottom line is that May will end up with a solid -SOI with sub -10 becoming increasingly likely, a strong leading indicator for El Niño.

Followup: similar with good chance of significantly BN SLP at Tahiti much of next week due to several pretty strong low pressures moving by to the south. It appears that most days for the rest of the month will be negative as it looks right now per model consensus.

As of 5/13, the SOI MTD is averaging -6, with the two stations contributing about equally to this modest negative. Looking at the model consensus out two weeks, it does appear that Tahiti SLP anomalies averaged out will be negative and Darwin positive. If anything, it appears to me that the SOI MTD will probably drop further as we go through the next two weeks. Thus, I see a realistic chance for -10 or so for full May SOI. IF that occurs, that would give this month the lowest SOI in at least 3 years and would be the lowest May SOI since 2015 and a decent signal for an oncoming El Niño. Since 1950, these Mays have had a sub -9 SOI: 1951, 1953, 1957, 1958, 1972, 1977, 1987, 1991, 1994, 1997, 2001, 2002, 2005, 2015 Of those 14, all were prior to an oncoming fall/winter Nino except 2001 and 2005. So, a sub -9 May is a pretty good indicator of an oncoming Nino.

Saying "potentially significant" is vague. Not only in using the word "potentially", but also the word "significant". One can argue that even just a moderate El Niño could be considered significant. One definition of significant is "likely to have influence or effect". A moderate El Niño is typically strong enough to have influence or effect. Most of us have known for quite some time that a moderate or stronger El Niño is likely on the way.

Thanks for posting this. We'll see whether or not this is a sign of things to come. Believe it or not, today's -31.31 is only the third sub -30 daily SOI since way back in July of 2020! Also, there has yet to be a long string of negatives this year. Actually, there hasn't been a negative daily string longer than 10 days since April of 2020! I'd want to start seeing longer than 10 day negative strings to have more confidence that the upcoming El Niño is starting to be significantly reflected up into the atmosphere. We're on a four day negative string now, which in itself isn't a big deal. Let's see whether or not this is going to turn into a much longer one.

Directly related to your 3rd Tweet regarding the idea of subtracting the warming of tropical oceans from the Nino 3.4 SSTA to produce a "relative Nino 3.4 index" or "RONI": "Another factor to consider is that the widespread ocean warmth may make it a little more challenging for the warm temperatures in the central-eastern equatorial Pacific to induce a tropical atmospheric response (maybe a reason for the current ENSO-neutral looking tropical atmosphere?). The reason is that the response of the tropical atmosphere depends on surface temperatures in the central-eastern equatorial Pacific relative to the surrounding regions. If those surrounding tropical regions are also warmer than average, then the bar is even higher for the Niño-3.4 region surface temperature anomalies to induce an atmospheric response (see footnote). The bottom line is that in terms of a push on the tropical atmosphere, we need to consider that the Niño-3.4 index may punch below its weight while it’s hovering in borderline El Niño territory, as it is now. However, if the central-eastern Pacific continues to warm up, we can expect that the atmosphere will feel that push eventually." Footnote: " This issue is why some, including Michelle of this blog, have advocated the monitoring of a relative Niño-3.4 or relative Oceanic Niño Index (RONI). The NOAA Climate Prediction Center monitors the RONI here. The RONI is simply our standard ONI (3-month average Niño-3.4 sea surface temperature anomaly) with the tropical average sea surface temperature subtracted. Such an index is less sensitive to a warming climate and, consistent with some of my earlier research, is more closely connected with changes in the tropical atmosphere than the standard ONI." ------------------------------ Since 2016, the RONI has averaged 0.4 C lower than ONI due to accelerated tropical ocean warming. So, my take is that the El Niño threshold based on RONI currently requires the ONI to reach +0.9 C and remain there for at least five straight trimonths instead of just +0.5 C for five trimonths to allow the atmosphere to act like there is a 3.4 based El Niño. Taking this further based on RONI: - moderate Niño currently requires ONI peak of +1.4 C instead of just +1.0 C - strong Niño currently requires ONI peak of +1.9 C instead of just +1.5 C - super strong Niño currently requires ONI peak of +2.4 C instead of just +2.0 C RONI might explain why the atmosphere in 2018-9 didn't act more typical of El Niño. Based on RONI, it would have been only warm neutral instead of weak El Niño. https://www.climate.gov/news-features/blogs/may-2023-enso-update-el-niño-knocking-door

1. Based on 1877-8 and 1888-9 being near normal in the NE US, I'm not going as far as to say "lock" to be warm in the NE US if 2023-4 ends up as a super El Niño. I'm be more in the "likely" (say ~70%) camp for that and ~25% chance for near normal. 2. In the SE US overall for the 7 identified super El Niño winters 1877-8, 1888-9, 1972-3, 1983-3, and 1997-8 were near normal. 1965-6 was colder than normal while 2015-6 was the only one warmer than normal. So, should it later look likely that 2023-4 is going to be super, I'd likely at that point lean toward near normal DJF temperatures in the SE along with wetter than normal for most places, especially nearer to the coast.

That's quite a rise forecasted for the PDO between April and July with still another 5 months to go even after that before winter starts. That suggests that a rise to low -1s is quite possible in July. That wouldn't be all that far from +0.50 being that there'd be five months to go. Do you know how accurate the various models are for the PDO? Are you aware of any biases?

I understand that the very low starting point minimizes the chance for it to rise enough to get to positive. But but based on a few cases of sharp rises when to a new Nino, might there be a small chance for at least a modest positive...say, DJF of +0.50+? Examples: 1. Nov-Apr 1883-4 was -1.4. DJF of the very cold 1884-5 was way up at +1.98. That's a 3.38 rise! 2. Nov-Apr of 1975-6 was -1.9. DJF of 1976-7 was up at +1.32. That's a rise of 3.22! 3. Nov-Apr of 2001-2 was -1.3. DJF of 2002-3 was up at +1.42 for a rise of 2.72! 4. Nov-Apr of 2022-3 was at -2.17. DJF of 2023-4 would reach +0.50 with a rise of 2.67. The rises in 1884-5, 1976-7, and 2002-3 would do it. The rises in 1884-5 and 1976-7 would actually give a strong +PDO (>+1.0) in 2023-4. So, there have been 38 new onset El Niños since 1855-6. So, 3 of 38 or 8% of them saw a PDO rise large enough to yield a +0.50+ in DJF of 2023-4. I used this table: https://www.ncei.noaa.gov/pub/data/cmb/ersst/v5/index/ersst.v5.pdo.dat

Why do you say BEST case for PDO is neutral?

1. In the SE US, half of your 6 listed El Niño winters following strongly -PDO Nov-Aprils were very cold: 1957-8, 1976-7 (coldest winter on record), and 2009-10 (coldest winter since 1977-8). Of those, 1976-7 had way above average snow in the deep SE with my area getting snow an unheard of three times. 2009-10 had well above average snow in Atlanta and the SE overall. The other three weren't cold, but all had above average wintry precip at ATL thanks to one big winter storm each of those winters. 2. Using another PDO table that goes back into the late 1800s, the 1884-5 El Niño also followed a strongly -PDO in Nov-Apr: https://www.ncei.noaa.gov/pub/data/cmb/ersst/v5/index/ersst.v5.pdo.dat That 1884-5 winter was quite cold in the E US, with NYC very cold with above average snow. Boston was also quite cold.

Also, 2023-4 is almost certainly going to me significantly stronger than just the +0.9 max anomaly in Nino 3.4 of 1976-7.