Today, NOAA dropped the likelihood of an El Niño episode to 58% (see here). This percentage has continued to fall since the spring, when it was suggested that an El Niño episode was 80% likely. In fact, according to some forecasters in the spring, a Super El Niño was likely to occur. When I wrote this article back in March, I wanted to recognize the potential for some type of El Niño event. However, I wanted to stress one thing...a super El Niño was very unlikely to occur. The biggest reason? The phase of the Pacific Decadal Oscillation. Below shows what the Pacific Ocean sea surface temperature anomaly should look like during each phase: warm/positive phase on the left and cool/negative phase on the right:
In the warm/positive phase, you can clearly see the warmer than normal water from the Gulf of Alaska, down the West Coast of the US, and in the Central Pacific Ocean. In the cool/negative phase, those anomalies are in different locations, with a predominantly “cool” Pacific basin.
Where are we now? Here are two versions of the current sea surface temperature anomalies:
You can see that we are currently experiencing PDO-positive (+PDO) conditions. Despite the fact that we started a long term (20-30 year period) -PDO about 9 year ago, we have briefly detoured to a +PDO since January. For those who prefer numbers to maps, here is a chart that shows the PDO phase based on the PDO index since 2005:
The numbers clearly show the trend since 2005 (far more negative values than positive), and clearly show the short detour we are currently experiencing. Brief detours from the mean PDO phase have occurred in the past and will occur in the future. You can see that when we track the PDO phase back to 1900:
The red spikes show the PDO in its warm/positive phase, while the blue spikes show the PDO in its cold/negative phase. For instance, we observed +PDO through the 1920s, 30s, and early 40s, before switching to -PDO in the mid-1940s. We then observed -PDO from roughly the mid-1940s until the late 70s (1977-78 considered The Great Climatic Shift). +PDO existed from late 1970s until about 2005, when it shifted wholeheartedly to -PDO. So despite us having observed +PDO since January, we can expect to revert back to -PDO in the near future. Based on the MEI since 1950, you can see the various El Niño and La Niña episodes that have occurred (red spikes El Niño, blue spikes La Niña):
A simple observation tells us that from 1950-1975 there were more, and stronger, La Niña episodes than El Niño episodes. From the late 1970s through 2005, there were more, and stronger, El Niño episodes than La Niña episodes. One of the biggest reasons I suggested earlier this year that a Super El Niño was unlikely, is due to the fact that strong El Niño episodes (such as those that occurred in 1982-83 and 1997) are extremely rare and not observed in this data set when the PDO was cool/negative. That being said, history shows that when the PDO briefly deviates from the long term phase, various El Niño or La Niña episodes can occur. That is also the reason I suggest that as long as this “deviation” is occurring, a weak to moderate El Niño episode is likely. Simply understanding PDO and ENSO history can help one deduce this and make a reasonably accurate forecast. It can also prevent you from bringing up the term Super El Niño when making said forecast. When I sat in on NOAA’s Winter Forecast conference call last month, I brought up this very point to them. I was told “I am not going to debate that with you here.”
I won’t always be right, and I certainly don’t pretend to be the smartest guy in the room when it comes to understanding or analyzing the PDO, however, I do have a solid grasp of it and its history. History is an amazing teacher and forecasting tool and one that gets ignored way too often. I simply think that if history would have been used as a forecast tool, the term Super El Niño wouldn’t have been uttered during the spring.
The puzzling thing about NOAA’s lowering of the Niño likelihood today, is that we are likely in a weak El Niño right now. Now I know “technically Niño conditions have to persist for 3 months” before classification can occur. However, three glaringly obvious signals...1) The MEI that I showed above suggests that we are in weak El Niño territory. 2) Sea surface temperatures in the Niño regions have been rising in the last month and look like this:
Three out of the four Niño regions have warmed up nicely in the last month and are currently meeting weak El Niño classification. 3) The Southern Oscillation Index (SOI) has been dropping like a rock and has been for a while, which allows an El Niño episode to develop and strengthen:
Today’s SOI is cratering again with a -27.2 contributing strongly to the monthly and 3 month mean. So while we won’t see a strong El Niño and possibly not even a moderate event, current conditions suggest we are already in a weak El Niño, and various model projections suggest we will stay there a while.
Based on history, I would expect the weak El Niño event to subside as we head into the summer, and I would also expect us to revert back to -PDO conditions in the second half of 2015 or early 2016. This will likely pave the way for a rather significant La Niña event sometime in 2016, but that is way down the road. A road, however, which I am always looking into...