Differences Between 2015-16 El Niņo
and Previous
Strong and Very Strong  Events

by Jan Null, CCM and
John Monteverdi, CCM
March, 2016

Some of the mantras from the past year from myself, John Monteverdi and many other responsible meteorologists, have been that each El Niņo is unique, that the number of past events to compare them to is quite small, and that there are "no guarantees". (For example see Misconceptions About El Niņo

As the current very strong El Niņo continues in the tropical Pacific, we are indeed seeing signifciant differences from past events; even those that are categorized as strong and very strong. Consequently, El Niņo 2015-16 is turning out to be the poster child for "Every El Niņo is Different"!

See also:  Comparisons of Precipitation and Zonal Wind Anomalies by Monthly Groupings for 2015-2016 with those for Five Strongest El Niņo Events since 1951, by Monteverdi and Null.

The Sea Surface Temperature Anomalies (SSTA) for the past year, when compared to previous strong and very strong events, are markedly warmer in the western Niņo regions (i.e., Niņo regions 4 and 3.4), while farther east in Regions 3 anbd 1+2 the current event is in the middle of the pack.  (Map of Niņo regions).

This can also be seen in the following Sea Height Anomalies, comparing this year to 1998.  Especially of note are the higher anomalies centered in the western portion of the El Niņo area of raised sea level heights with nearer to normal heights along the South Amercian coast.


The sections above summarize the sea surface temperature anomalies for the six strongest El Niņo events since 1951.

In this section, we examine the impact of those anomalies on aspects of the circulation.   The documented impacts of the temperature anomalies on the circulation include the creation of stronger than average zonal flow, basically a subtropical branch of the westerlies, in the lower subtropics.  

The charts below present the differences in the 500 mb zonal wind averaged for November 2015 through January 2016 and that composited for the other five strong or very strong El Niņo events since 1951, and that for each of the other five strong El Niņo years since 1951.  Blue fill indicates that the zonal winds were weaker for the current event.

As you can see, the largest difference between the zonal wind this year compared to the composited zonal wind for the other five has been much weaker than normal westerlies in the lower subtropics.  Essentially, the expected subtropical branch has been weaker than that experienced in the other years, or even absent.

A comparison of the zonal wind this year with that of each individual strong or very strong El Niņo year in the subtropical portions of the Pacific shows that the differences between the subtropical zonal flow were the greatest between those this year and those in 1997-98, followed by 1965-66; 1982-83, 1972-73 and finally, 1957-58.

The zonal winds for the period November 2015 through January 2016 were most similar to those for 1957-58.



This year there have signficant differences in the precipiation patterns when compared to previous strong (i.e., Oceanic Niņo Index [ONI] between 1.5 and 2.0 for 1957-58, 1965-66, 1972-73) and very strong (ONI ≥  2.0) El Niņos (1982-83 and 1997-98).

In comparing the current event (2015-16) to the previous strong and very strong El Niņo events, there is no clear analog. The most striking difference in the Pacific Northwest where there is a very strong postivie rain anomaly. There are some consistencies in the eastern half of the United States, with the Southeast being consistently wetter than normal except fo 1965-66, but the drier than average Northeast best matches the winter of 1982-83.

This year's temperature pattern best matches 1982-83 but are consistently warmer than even that year.

But what does it mean?  It will take a considerable analysis to better understand why this year is different from previous strong and very strong events, but in the short term it remains a reminder that "All El Niņos are different"!
Send comments and questions to
Jan Null or John Monteverdi.