Saturday, March 22, 2014

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.