El Niño Beginning to Reach Surface

It looks like the much-anticipated El Nino is currently reaching the surface in the eastern Pacific.

Latest sea surface temperature anomalies (SSTAs) over the globe show our El Nino beginning to blossom in the sporadic areas in the waters west of Ecuador. This has been a long time coming, as we have been discussing extensively the Kelvin Wave that has been producing record-breaking temperature anomalies, as high as 6 to 7 degrees C above normal! The wave has been slow to push northward due to a not-as-favorable environment above the surface, but now that we are seeing the El Nino evolve, it can be expected that we will be in at least moderate El Nino territory by the time we hit late autumn.

Mean water temperatures along the equator from the surface to 500 meters down (top),
and anomalies for the same cross-section region (bottom).

If we take a look at sea surface temperature anomalies, now diagnosed on a cross-section along the equator from the surface to 500 meters down, it is evident that this Kelvin Wave-produced warm water is quickly upwelling to the surface. We see anomalies as high as 6 degrees C above normal about fifty meters below the surface, as is seen on the bottom panel in the top-right corner. As this body of warm water continues to push to the surface, we will likely see gradual weakening of these anomalies, but they should still be strong enough to propel us into our first El Nino event in multiple years.

Andrew

Strong El Niño May Be Materializing Faster Than Predicted

The strong El Nino that was discussed in a recent post, where we analyzed the possibility of an El Nino that may rival the 'Super El Nino' event(s) of the past, may be forming now- far sooner than originally thought. Note: This post is an update to my previous post on the impending El Nino, which can be accessed by clicking here.

Let's refresh our memories about the El Nino-Southern Oscillation phenomenon.

The image above shows sea level anomalies associated with the El Nino phase of the El Nino-Southern Oscillation (ENSO) phenomenon, as well as the La Nina phase. As is shown, an El Nino sees substantially higher than normal sea levels in the eastern Equatorial Pacific, while a La Nina sees below normal sea level anomalies. In the same sense, an El Nino observes warmer than normal waters over those same areas, and a La Nina depicts colder than normal waters in the same blue and purple areas shown.

The image above shows observed values of the Southern Oscillation Index, also known as the SOI. The SOI is calculated by observing pressure differences between Darwin and Tahiti near the Equator. Negative values of the SOI, namely below -8, indicate the dominance of El Nino-like conditions, while positive values above +8 show the presence of La Nina conditions. This graph goes back to January 2012, when we began to see a consistent negative SOI values. However, we then returned to typical fluctuations of the SOI in 2013. It is only now, in March 2014, that we have observed an absolute crash of the SOI in recent days, well into definitive El Nino territory. This collapse of the SOI well into negative values tells me the atmosphere is priming itself for the onset of the El Nino that we discussed a few days back. We've known for a while that the El Nino is on the way, but the SOI crash indicating an El Nino arising is happening far faster than originally predicted. But how can we know this is an actual El Nino emerging, and not just your normal fluctuation of the SOI?

The graphic here shows water temperature anomalies by depth over the eastern Equatorial Pacific, more specifically from the 140E longitude line to the coast of Ecuador, right along the Equator. Let's take a look at the top panel of this graphic, which shows the anomalies by depth (the bottom panel shows temperatures by depth, not anomalies). What we see is quite startling- there is a body of extremely warm water just under the surface of the Equator, controlling the waters 100 meters to 200 meters below the surface.  This swath of warm water tells us that there is a Kelvin Wave afoot.

This graphic, drawn up by Mike Ventrice, shows the sort of situation we're experiencing with the Kelvin Wave. As the Kelvin Wave pushes east, we see sea level anomalies rise in conjunction with the anomalous warmth. Ahead of the Kelvin Wave, we then see downwelling, which lowers sea levels and cools sea surface temperatures, leading to a 'false Nina', where the SSTAs might tell us there's a La Nina, but it's actually just a byproduct of the Kelvin Wave beginning to push east. 

This Kelvin Wave has been sitting in the waters below the Equator for some time now, but it is only recently that we're seeing the Kelvin Wave actually start to impact the surface waters. We can see how this is happening, as the temperature anomaly by depth image above shows two arms of warmer than normal waters stretching from the Kelvin Wave up to the top of the image. It's no surprise that the Kelvin Wave is impacting the surface. What is surprising, though, is how fast this is happening- the formation of an El Nino was expected to be around a 2-4 month timeframe, but now we could be looking at formation in just a matter of weeks.

We're also seeing skyrocketing upper ocean heat anomalies, confirming the idea that this is a true El Nino, and not just some random SOI fluctuation or the odd, small body of warm water pushing to the surface.

A more startling feature of this phenomenon is, even though we're seeing the warm water push to the surface, the Kelvin Wave is getting stronger rather than weaker.

This image shows three panels of observed sea surface temperatures on March 20th. We see climatology of sea surface temperatures (SSTs) on the top panel, actual observed SSTs in the middle panel, and anomalies of the observed SSTs on the bottom panel. We're going to be focusing on the bottom panel, where we can see the full strength of the Kelvin Wave. If you go back to the Super El Nino post, we saw the last observation of the Kelvin Wave at abut +5.35º C above normal. However, this image shows how the Kelvin Wave has strengthened to +5.64º C above normal- a +0.29º C increase in just a week! When you take into account that the Kelvin Wave that produced the 1997 Super El Nino was only +4.3º C above normal at the same time as this image (in March of 1997), it looks like we might be looking at the strongest Kelvin Wave observed to date. This would help the idea that we're looking at a Strong El Nino to evolve in the next few months (or weeks depending on how fast the Kelvin Wave propagates to the surface).

All of this tells me we are looking at the El Nino arriving much sooner than first predicted. Rather than the original 2-4 month timeframe I had been planning, it's possible we see an El Nino in just 4 to 8 weeks. I wouldn't be surprised if we saw the emergence of a moderate El Nino in about 6-12 weeks from today, with a strong El Nino arising in as soon as 12-16 weeks. This may seem like a long time, but when you consider my original projection for a potential strong El Nino was after August 2014, this is certainly a much sooner projection, reflective of what the Kelvin Wave has been doing in the last week or so.

Impacts on the United States include a potentially more active severe weather season, which I will address in my 2014 Severe Weather Season Outlook, to be issued tomorrow (Sunday). We may also see a more suppressed hurricane season, and this will be addressed in my 2014 Atlantic Hurricane Season Outlook, which will come out later on in April.

Andrew

Thoughts on ENSO, East Coast Snowstorms and Spring

This post will address my thoughts on the ENSO situation, the potential for East Coast snow events in the near-future, some additional spring thoughts, and more information on the upcoming severe weather season. This post will be of the more technical variety, so there will be a summary at the bottom for those who may not know as much weather jargon as some others do.

Above, we see the latest data from each monitoring region of the El Nino Southern Oscillation (ENSO) phenomenon. The blues represent below normal sea surface temperature anomalies (SSTAs), while oranges show above normal SSTA values. The El Nino phenomenon is characterized by above normal sea surface temperatures, and the La Nina is shown by below normal sea surface temperatures. Looking over all of the regions, we see that most of them are in a strong cooling period, actually hitting La Nina criteria of -0.5 degrees C anomaly or below. However, Nino region 4 is experiencing sudden warming to El Nino levels of 0.5 degrees C anomaly or above. Nino region 4 is the furthest west of the four regions, as the graphic below shows.

So what's making this region warm so quickly? Well, the answer lies in the sharp cooling trend we've seen in the regions further east, like Nino regions 3.4 and 3.

There's a Kelvin Wave afoot.

Shown above is a two-panel graphic, depicting SST anomalies on a depth by longitude chart on top, as well as a mean equatorial temperature depth-longitude chart on the bottom. Looking at the SST anomaly chart, it is very clear that there is a strong Kelvin Wave present under the surface. Kelvin waves are defined as 'warm spots' in the ocean that traverse the Equatorial Pacific, beginning near Indonesia and ending around Ecuador and Peru. The Kelvin Wave is actually a massive-but-small wave, meaning that while the water height only rises by a couple inches when the wave moves through, the Kelvin Wave stretches a vast expanse of water, and its effects on the climate are even more significant. During an El Nino, we see warmer than normal waters over the surface of the four Nino regions. Kelvin Waves can help to speed up the El Nino process by bringing an expanse of warm water into the Nino regions, about 100 to 200 meters below the surface. If it's 200 meters underwater, how can Nino region 4 at the surface be warming up? Well, check out the top of the SST anomaly image. I circled an area where a finger of warmth has propagated to the surface, and that is what's causing the sudden warmth. But the Kelvin Wave isn't responsible for just the warming aspect; it's also responsible for the significant cooling we're seeing in Nino regions 3 and 3.4.

This graphic, drawn up by Mike Ventrice, shows the sort of situation we're experiencing with the Kelvin Wave. As the Kelvin Wave pushes east, we see sea level anomalies rise in conjunction with the anomalous warmth. Ahead of the Kelvin Wave, we then see downwelling, which lowers sea levels and cools sea surface temperatures, leading to a 'false Nina', where the SSTAs might tell us there's a La Nina, but it's actually just a byproduct of the Kelvin Wave beginning to push east.

This phenomenon of warming-before-cooling has been observed well with the last few Kelvin Waves, as this chart shows. We saw one wave crossing the Pacific in September 2013, with little to no cooling before it; we saw a second wave present in November to December 2013, which did provoke some noticeable cooling before the wave traversed the Pacific, and the latest wave looks to be the strongest one of the three, with even stronger cooling occurring just before the warming. If you think about it, a case can be made for the strength of downwelling before the Kelvin Wave determining the strength of that Wave, as it seems the stronger downwelling episodes occur before the stronger Kelvin Wave episodes. The other Nino regions are experiencing anomalous cooling due to this downwelling, as the circled portion in the chart above shows.

The Kelvin Wave has shown up noticeably on sea level anomalies...

...As well as upper ocean heat anomalies.

Both of these indicators point to the idea that we're probably about to exit this neutral ENSO/cool-neutral ENSO situation we've been in for the last couple of years, and a transition to an El Nino seems more likely. Model guidance has been simulating this rise to a moderate El Nino by fall very well.

The next question becomes, will this Kelvin Wave actually make it to Ecuador and Peru? In order to find out, we have to turn to the western Pacific.

Shown here is a map of 850mb winds (arrows), outgoing longwave radiation (contours) and outgoing longwave radiation anomalies (colors) from the period of January 22nd, 2014 to January 28th. We're going to focus in on the portion of this map I boxed in. If we look at that section, we see the arrows pointing down and converging on the Equator before then pointing eastward. This phenomenon is the result of two Pacific gyres on opposite ends of the Equator. This means that there were two low pressure systems, one on either side of the Equator, that were spinning air towards the other in such a fashion that then allowed the air to be pushed off to the east. How is this possible? Considering low pressure systems north of the equator rotate counterclockwise, and low pressure systems south of the equator rotate clockwise, the winds from each system can combine and push their combined winds off to the east, which can then help with the movement of the Kelvin Wave.

The graphic above gives a good picture of what these two Pacific gyres end up doing. Considering we saw one of these double-gyres in late January, and another one is about to get going, the Kelvin Wave should continue to push to the east, and ought to be able to affect all Nino regions. This raises the question, could we see an El Nino by next winter? I'm comfortable putting down a 'yes' for that question.

Now, the warming of the westernmost Nino region 4 will likely have impacts on our severe weather season. How? Take a look at the chart above. This graphic shows correlations of 200mb winds based on the Nino 4 phase. In simpler terms, for example, when the Nino 4 has below-normal waters, the oranges and yellows (which signify positive correlation areas) would then experience below-average winds. The areas shown in blue (which signify negative correlation areas) would then see stronger than normal winds. In this case, since we have warmer than normal sea surface temperature anomalies over Nino region 4, we ought to watch for at least a slight strengthening in the subtropical jet stream as we enter March, due to the positive correlation depiction over the southern US. Because the current warming is just a little piece of a Kelvin wave and not yet a legitimate El Nino, I'm not expecting the subtropical jet stream to completely go nuts and strengthen out of control. However, it wouldn't surprise me to see the STJ strengthen in the next couple of weeks as a result of this correlation. And, if we have a stronger subtropical jet stream, the risk of severe weather then goes up. Hence, we need to watch out for the severe weather season to ramp up in coming weeks, not only due to the gradual retreat of this harsh winter, but also due to the slightly-strengthened subtropical jet stream.

Let's switch gears and discuss my thoughts for the end of March and into April (forecast for late February and most of March here), as well as why I feel we need to watch out for a snow event along the East Coast in the middle of March.

This image shows 500mb height anomalies over the Northern Hemisphere during the January 22 - January 28 period of this year. In this reanalysis, we see strong ridging over the west coast of North America, producing a northwest flow situation into the East Coast, where a lobe of the polar vortex sat to the north in Canada. Something we can use here is the Lezak Recurring Cycle. The Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a regular, unchanging 40-60 day interval for the next ~10 months before it dissipates over the following summer. If we utilize the Lezak Recurring Cycle for this timeframe, we can extrapolate the January 22-28 period out 57 days (which is the current length of the LRC this season), we arrive in mid-late March. This means that it's very possible we see this late January pattern come back around in late March, northwest flow included. The reason I'm discussing this northwest flow so much is because it has the potential to not only bring us an East Coast snow threat in mid-March, but also has the potential for a severe weather event.

As I discussed above, the subtropical jet stream could be strengthened as we enter March thanks to the warming of Nino region 4. If that occurs while we are in a northwest flow situation in mid-late March, it's very possible we come across a favorable environment for a spring coastal storm. I'm not saying we'll see one for sure, but the last time we saw a northwest flow come about and I thought there might be an East Coast snow event as a result, it ended up coming to fruition.

These images show some possible scenarios for northwest flow severe weather outbreaks, where we would have a lobe of the polar vortex displaced in eastern Canada, with strong ridging along the west coast of North America. Due to the warm pool in the northeast Pacific, it's entirely possible we see sustained ridging stick around in the western portion of North America like we saw in the late January image earlier in this post, which would then lead to some northwest flow severe weather opportunities and snow potentials. Both types of inclement weather potentials would be assisted by the stronger subtropical jet stream.

If we take a look at the 500mb anomaly chart a week after the January 22-28 chart earlier in this post, we see that the environment over the January 29-February 4 period has changed. The ridging has shifted westward into the Bering Sea, leaving the lobe of the polar vortex to weaken and move out of the way, which then results in ridging along the East Coast. I would expect this sort of environment to come back in the closing days of March and opening days of April in accordance with the LRC. In that time period, we may be looking at severe weather threats displaced further west and north, with warmer weather for the East and cooler weather in the West. By this time, we will have probably seen the end of big winter storms, with the exception of a rogue snow event in the northern Plains before winter finally leaves the United States.

To sum up:

•Warming waters in the Equatorial Pacific could have long term consequences for the weather pattern in spring, summer, and into next winter.
•Due to those warming waters, severe weather chances may be enhanced later in spring.
•We are watching for a potential snow event in the East Coast in mid March.
•Late March into April may feature a warm East and cool West.

Andrew

Kelvin Wave Provoking El Nino; Atmosphere in Disagreement

A Kelvin Wave currently moving across the eastern Pacific appears to be trying to provoke an El Nino, but the rest of the atmosphere is in disagreement.

The graphic above shows water temperature anomalies across the Equatorial Pacific, with longitude values on the bottom legend and depth values in meters on the left legend. The Kelvin wave is clearly shown by the strong positive water temperature anomalies from the 100 to 200 meter depth in the central/western ENSO monitoring area in the Equatorial Pacific. With a Kelvin Wave, you have a mass of warm water pushing east under the surface, and pushing east across most (if not all) of the Equatorial Pacific. This wave warms the waters below the surface, and if those subsurface waters are mixed to the surface, we can see an El Nino develop. Due to that process, Kelvin Waves are typically associated with El Nino formations, and that is why we are monitoring this event for possible El Nino provocation down the line in spring.

However, the rest of the atmosphere does not agree that we will see an El Nino anytime soon.

One feature we see over the Eastern Pacific is a swath of anomalously strong upper level winds, as the purples and yellows on the attached image denote. Thanks to the Earth System Research Laboratory (ESRL), we can compare these uppr level winds to see what ENSO state the atmosphere is currently in- a La Nina, El Nino, or neutral-ENSO state.

If we look at the ESRL's 200mb wind anomaly composite for February and March over the Equatorial Pacific, we see that El Nino's are typically recognized in those time periods by strong upper level winds due west of Mexico, with anomalously weak upper level winds over the ENSO monitoring area. Taking a look back at the latest observed upper level winds, it is clear that the atmosphere is in more of a La Nina state, as we usually see strong upper level winds over the eastern Equatorial Pacific during an El Nino instead of weak upper level winds we are currently seeing.

Another item we can use to judge what state the El Nino-Southern Oscillation phenomenon is in is the sea level anomaly. In other words, we can see if the waters over the eastern Equatorial Pacific are higher or lower than normal, and use that to help tell us what phase the ENSO is in. If we check out the composite graphic above, it is clear that the El Nino phenomenon is identified by higher than normal sea level anomalies, with the La Nina producing lower than normal sea level anomalies. The November 1997 sea level composite on the top of this graphic shows the El Nino sea level anomaly, while the February 1999 composite below that depicts sea level anomalies for a La Nina.

Taking a glance at the latest observed sea level anomalies, it is more apparent that while we aren't in an El Nino, which would show up as a swath of yellows and oranges to indicate higher than normal sea level anomalies, we also aren't in a defined La Nina, which would appear as a swath of deep blues on the right hand side of this chart. We do see some blues in the Equatorial Pacific, which could argue for a weak La Nina if you really want to be picky about it, but I'm not really seeing any defined ENSO state going one way or the other.

This chart, showing the anomalous depth of the 20 degree (C) isotherm over time, gives you a hint at what the progression of a Kelvin Wave looks like, with two clear examples of Kelvin Waves observed in November 2013 into January 2014, and from September 2013 into October 2013. The latest observation of this 20 degree isotherm confirms that we are looking at a Kelvin Wave. with this wave looking to be the strongest out of the last three events. It's possible that this sends us into an El Nino pattern when spring and summer come around, but for now, an El Nino does not look to be on the way, at least for the near future.

Andrew

Preliminary ENSO Outlook for Winter 2014-2015

As we close out the winter of 2013-2014, I suppose it's time we start looking at forecasts for the El Nino-Southern Oscillation (ENSO) phenomenon for this summer to see what ENSO state we may see in the winter of 2014-2015.

Before we begin, let's establish what the El Nino-Southern Oscillation is.

The El Nino-Southern Oscillation (ENSO) phenomenon involves sea surface temperature anomalies over a portion of the Equatorial Pacific, namely focusing on the waters west of Colombia and Ecuador. In the image above, the Climate Prediction Center shows distinct El Nino environments (left two panels) and La Nina environments (right panels). During an El Nino, water temperatures to the west of Ecuador usually warm up significantly. These warm temperatures then produce anomalously high levels of tropical convection (as warm waters make air rise, creating thunderstorms), and the whole process leads to an El Nino pattern. During a La Nina, we see the opposite, where colder than normal water temperatures are observed, leading to anomalously low levels of tropical convection. As you can see by the image below, the El Nino patterns and La Nina patterns during the winter months have different impacts on the US.

Now that we know what the ENSO phenomenon is, let's move on to the model forecasts.

We'll begin with the NCEP's CFS model. The CFS projects monthly and seasonal values for the ENSO phenomenon, and also gives out precipitation, SST, temperature, etc. forecasts for the world. The CFS model indicates we will see steady rising of sea surface temperatures in the Equatorial Pacific throughout the spring, summer and beginning of fall, before we reach SST temperature anomalies above 1 degree Kelvin, which is equal to over 1.8 degrees Fahrenheit. This would qualify as a strong El Nino, something we haven't seen for a while (we have been in an unprecedented lack of El Nino events since 2010; the four-year stretch since 2010 has included neutral ENSO and La Nina events). This strong El Nino would then likely continue on into the winter of 2014-2015. However, because the CFS model is notorious for forecasting an El Nino that never comes true, I'm not buying this forecast. While I do believe we see an El Nino event by this summer 2014, I don't believe it will be a strong El Nino.

Next, we will continue with the ECMWF model's forecast. The ECMWF model projects the ENSO phenomenon out to roughly 6 months forecast time, and uses its prestigious 52-member ensemble prediction system in its forecast. The ECMWF model also projects that we will see an El Nino by the summer, though its rise to an El Nino is more exponential than linear- we saw the steady rising trend in sea surface temperature anomalies (SSTAs) in a linear fashion by the CFS, and now we see an exponential increase in SSTAs around May and June 2014. By July 2014, ECMWF ensemble guidance has water temperatures at 1 degree Celsius above normal, which equates to 1.8 degrees Fahrenheit above normal. This would also qualify as a strong El Nino, but once again, I'm skeptical of these strong El Nino forecasts. While they're possible, I'm not so sure they're probable.

Next, we'll take a look at the Japanese ENSO model prediction. The Japanese model forecasts the ENSO phenomenon out to just after July 2014, about the same forecast time period as the ECMWF model. The Japanese model goes for a forecast similar to the ECMWF, where we see a jump in SSTAs around May and June, before arriving in the ~0.8 to 0.9 degree Celsius anomaly. That would constitute an El Nino, though it would be weaker than projections by the CFS and ECMWF. I find this forecast much more logical- it's always a gamble when you go with strong El Nino or strong La Nina forecasts. Usually its better to go with a weaker, albeit still substantial forecast.

Next up is the Australian Bureau of Meteorology's POAMA model. The POAMA model projects the ENSO phenomenon out to October, with a forecast time period of roughly 8 months. The POAMA model takes the current cool-neutral ENSO state to neutral by June, and borderline-El Nino by October. This forecast might be a little too weak with the idea of an El Nino- I wouldn't be surprised to see an El Nino declared by late summer (around August or September). However, the POAMA does give us a glimpse at the other side of the forecast envelope, when comparing it to the bullish ECMWF/CFS forecasts.

Next, we'll take a brief glance at this trio of forecasts. These three forecasts are under the LDEO model domain, which gives forecasts out to December 2014, meaning its forecast time period is roughly 1 year when we see that the red observation line stops at December 2013. In these three projections, we see that a weak El Nino or warm-neutral ENSO state is favored by the winter of 2014-2015. I expect we see an El Nino by this time, so these models may be a little too under-aggressive with this situation.

The next item to analyze is the NMME model suite. The NMME is a compilation of various global model guidance systems, all of which project the ENSO phenomenon using an ensemble set out to 8 months. In this graphic, we see the projected ENSO values by operational and ensemble members from the CFS model (red), two separate versions of the CMC model (CMC1 in green and CMC2 in navy blue), the GFDL model (light blue), NASA's model (pink), NCAR's model (yellow), and the NMME suite mean (black dashed line). The NMME suite is in decent agreement on a steady rise to El Nino conditions by the end of summer, something I do believe is likely. The NMME mean has the El Nino in weak to moderate condition by August, something I think is more probable than possible, especially considering history would suggest an El Nino is long overdue this next winter. In summary, I agree with the NMME projection.

The next suite of models to observe comes from the International Research Institute for Climate and Society. These models project the ENSO phenomenon out to the August-September-October period, meaning the forecast timeframe is around 10 months. This graphic gives us a look at a variety of model guidance systems from around the world. Each different model is displayed in a different color, with the average ENSO prediction shown in the solid yellow line. We see that the ensemble prints out a borderline-El Nino by the fall months. Considering we are almost certainly heading towards an El Nino next winter, this forecast is a good median in the envelope of forecast models.

This final model shows the SST anomaly forecast for the December-January-February 2014-2015 period from the SCRIPPS institute. The SCRIPPS institute model projects the ENSO Phenomenon out to this DJF period. We can see that the model shows a strong El Nino by late winter. As I've gone through all of these models, some of which have been showing a strong El Nino, I still hold my belief that these models are likely too strong, and a weak to moderate El Nino is more likely. These details will be cleared up in the months ahead, of course.

Andrew

Atmosphere Finally Recognizing El Nino

Multiple indices are beginning to show a transition into El Nino signal territory, where the index in question shows that conditions similar to that of an El Nino are being seen. Above is the Global Atmospheric Angular Momentum, or GLAAM (also called AAM). If we look at past GLAAM values, we see that they have been staying in La Nina territory for a while now. However, I circled a new bounce in the GLAAM that has pushed the index into El Nino territory. Could this be a sign that the atmosphere is recognizing the El Nino? I wouldn't doubt it.

This second image is of the Global Wind Oscillation, or GWO. It is closely tied into the GLAAM, but pretty technical, so I'll just explain what it all means. Basically, the bottom half of the image (Phases 1-4) are defining a La Nina, and the top half of the image (Phases 5-8) are defining an El Nino. The middle circle, while colored, defines the GWO is too weak to affect the weather. Recently, the GWO has been staying in Phases 1-3, meaning weak La Nina conditions. However, if you follow the bright green line on the right half of the image, you will see the most recently observed conditions have been floating into Phase 4, going into an El Nino phase.

It appears that at least some of the atmosphere is starting to recognize the presence of an El Nino. While this is one of dozens of factors linked to seeing the El nino appear in the atmosphere, this is definitely a first step.

Andrew