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Details on the June 2014 ENSO discussion

Today, the Climate Prediction Center (CPC) released the June ENSO Diagnostic Discussion.  Chances that an El Niño will occur by summer are above 70%, and reach 80% by the fall. Sea-surface temperature anomalies increased across all the Niño index regions in May; the latest weekly value of the Niño3.4 index is now above +0.5°C. Tropical rainfall across Indonesia and the Pacific remain close to average, but forecasters are confident that the atmosphere will begin to respond to the ocean and El Niño will develop, likely in the next few months.

Recently, there’s been a lot of speculation about how strong this El Niño will be, especially considering the strong westerly wind bursts in late winter, and the large subsurface temperatures in early spring. The subsurface temperatures in March, which was a record for the month going back to 1979, inspired comparisons to the early stages of the 1997/98 El Niño, the largest on record (ONI maximum of 2.4). That event also developed in the spring, like this one. However, right now, forecasters are not favoring a strong event (while not at all ruling it out) and believe a moderate event (ONI 1.0 - 1.5) is slightly more likely, sometime during the fall/winter. So what’s going on?

First, the subsurface temperatures have tapered off a bit recently (Figure 1). While still substantially above normal, the average of the upper-ocean (300m to surface) temperatures in the tropical Pacific has decreased over the past two months. SSTs tend to lag this measurement, often by a few months and with lesser intensity.

Equatorial ocean upper 300-meter temperature anomaly

Figure 1: Equatorial ocean upper 300-meter temperature average anomaly during January-December of 1997 and 2014.

The difference between 1997 and 2014 are also illustrated by the May cross-sections of temperature anomaly along the equator (Figure 2). If you’re interested, you can check out the history of ocean temperature anomalies and compare other El Niño events, such as 2002/03 or 2009/10, at a new CPC site.

Subsurface temperature cross-sections

Figure 2. Subsurface temperature (degrees C) cross-sections from May 1997 (left) and 2014 (right).  The figures are showing the average of several different subsurface temperature datasets. Maps based on data from the Real Time Multiple Ocean Reanalysis Intercomparison website.

Another factor the forecasters are considering is the model guidance. Most climate models are predicting a weak-to-moderate event, with dynamical models slightly favoring a moderate event and statistical models favoring a weaker event.  The ensemble mean of NCEP’s Climate Forecast System, CFSv2 (Figure 3, black dashed line) has been fairly consistent in forecasting Niño3.4 anomalies in the range of 1.0-1.5°C, but, as you can see from the individual model runs (blue, red, and gray lines), there is an envelope of possible values from 0°C to slightly above 2.0°C.

Predicted departures from seasonal average temperature in the tropical Pacific through 2014

Figure 3. Predicted departures from seasonal (3-month) average temperature for the Niño3.4 region of the tropical Pacific through the remainder of 2014. Plot based on data from the NCEP coupled forest system (CFS) version 2.

 

We’re beginning to move beyond the “spring barrier” (when models have a harder time accurately predicting future conditions) and will be watching the ENSO model forecasts closely going forward. Regardless, predicting the peak strength tends to be the most difficult part of ENSO forecasting.  

So... if we have an El Niño by this fall, be it weak, moderate, or strong, what does it portend for the wintertime precipitation and temperature over the U.S.? Stay tuned - we’ll have a post about this very topic within the next week.

Thanks to Yan Xue for her help with this post.

 

 

Comments

Emily: Thank you for the update, and for the links to the new Real Time Multiple Ocean Reanalysis Intercomparison website. I’ll make sure to include links to it in one of my upcoming posts about the 2014/15 El Nino at my blog and at WattsUpWithThat. Regards Bob

I found the site very interesting and informative and presented in a very understandable format. After having more time to review individual elements I may have more specific comments.

With the sun(sun spots and TSI) and PDO close to the same as it was in 1972 looks like a close repeat of that el-nino of 72-73 will occur. Time will only tell.

Your comparison of 1997 and 2014 plots would have been clearer if: you had labeled the ordinates (depth in meters? feet? fathoms?), the graphs as temperature ANOMALIES, and specified what ranges of latitudes were used. When we are presented with a graph with longitudes as the abscissa we usually assume it is a MAP.

I do appreciate your efforts to provide a good and objective paper, however one thing you should perhaps mention is that we are now in the middle of a cold interdecadal period (which probably will last till mid 2020); in 2012 something like this happened, many scientist were confirming El Nino, but finally just a modoki occurred; the reason behind is that we are in cold PDO and I think this fact is not being taken into account. Nowadays, how the heat content has decreased significantly in the last weeks, and how subsurface T anomalies has receded could suggest that El Nino (if happens at all) will be weak in intensity and short lived, unless a new kelvin wave start travelling west-east (is that possible?). In any case the best thing is to wait till August to have a better picture. I will be visiting this site.

The influence of decadal variations on seasonal evolution of ENSO is an interesting question and not one that is well understood.  A few forecasters might factor the decadal "regime" into their forecasts just slightly (by tweaking the probabilities a few percentage points here and there) but it remains an open question how much the the lower frequency decadal background state should be considered in seasonal ENSO forecasts.   Going forward, another westerly wind burst and ocean Kelvin wave could develop, but there is no clear sign of one on the horizon at this point. 

In reply to by Franklin Ormaza

Emily: thanks for your info about enso. It seems that it warm everywhere around E.Q. in time-longitude section of SST anomalies (5°N-5°S) chart. I just wonder, is it possible that this year is not a " typical enso " ? Or a possible CP type of enso.

I appreciate the wealth of information available but I am looking for opinions regarding El Nino and likely changes from the norm November 2014 to Feb 2015 Micronesia South to Equator. I am sailing a yacht Fiji to Malaysia and trying to gather info on the best routing regards a likely El Nino event. Stay well North and find wind or stay South, lose the wind but reduce the risk of typhoon.

As a sailor myself, this question is very interesting! El Nino is associated with less activity in the south Pacific tropical cyclone region, but of course it is always a good idea to keep an eye on the weather forecast. The Australian Bureau of Meterology tracks cyclones in this region, and they should have an outlook for the 2014-2015 season relatively soon. (They do an outlook specifically for the South Pacific Islands that may be interesting for your planning.) The reduced trades characteristic of El Nino are likely to hamper your progress, however.

I am a dam operator on the lower Colorado River. In fact the last control structure on the river, the Imperial Dam. While we are not a storage dam in the sense of Hoover or Glenn Canyon (we are a diversion dam), we play a vital role in the delivery of water to Southern California and Arizona. A strong El Nino will have a HUGE impact on our scheduled deliveries. Weather in general plays a big part in over-runs and shortages on the river. Every cubic foot of released water has a destination, farming mostly but cities and municipalities too. Extra dry or extra wet weather as you can see is very important for us to know. So glad I found your informative, easy to read site! You are book marked and will be back often, Thanks!

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