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Please refer to our licensing agreement for permission to use IRI ENSO materials. The CPC/IRI materials are not included in this licensing.

IRI ENSO Forecast

2017 September Quick Look

Published: September 14, 2017

A monthly summary of the status of El Niño, La Niña, and the Southern Oscillation, or ENSO, based on the NINO3.4 index (120-170W, 5S-5N)

Use the navigation menu on the right to navigate to the different forecast sections

In mid-September 2017, the tropical Pacific remained in an ENSO-neutral state, although SSTs in the east-central tropical Pacific have cooled to near the threshold for La Niña while the atmosphere continues to maintain largely ENSO-neutral patterns. The collection of latest ENSO prediction models indicates coolish ENSO-neutral or weak La Niña as two possible scenarios during Northern Hemisphere fall and winter. The official CPC/IRI outlook slightly favors La Niña development, and carries a La Niña watch.

Figures 1 and 3 (the official ENSO probability forecast and the objective model-based ENSO probability forecast, respectively) are often quite similar. However, occasionally they may differ noticeably. There can be several reasons for differences. One possible reason is that the human forecasters, using their experience and judgment, may disagree to some degree with the models, which may have known biases. Another reason is related to the fact that the models are not run at the same time that the forecasters make their assessment, so that the starting ENSO conditions may be slightly different between the two times. The charts on this Quick Look page are updated at two different times of the month, so that between the second and the third Thursday of the month, the official forecast (Fig. 1) has just been updated, while the model-based forecasts (Figs. 3 and 4) are still from the third Thursday of the previous month. On the other hand, from the third Thursday of the month until the second Thursday of the next month, the model-based forecasts are more recently updated, while the official forecasts remain from the second Thursday of the current month.
Click on the for more information on each figure.

Historically Speaking

    El Niño and La Niña events tend to develop during the period Apr-Jun and they
  • Tend to reach their maximum strength during October - February
  • Typically persist for 9-12 months, though occasionally persisting for up to 2 years
  • Typically recur every 2 to 7 years

IRI ENSO Forecast

CPC/IRI ENSO Update

Published: September 14, 2017

El Niño/Southern Oscillation (ENSO) Diagnostic Discussion issued jointly by the Climate Prediction Center/NCEP/NWS and the International Research Institute for Climate and Society

ENSO Alert System Status: La Niña Watch

Synopsis: There is an increasing chance (~55-60%) of La Niña during the Northern Hemisphere fall and winter 2017-18.

Over the last month, equatorial sea surface temperatures (SSTs) were near-to-below average across the central and eastern Pacific Ocean (Fig. 1). ENSO-neutral conditions were apparent in the weekly fluctuation of Niño-3.4 SST index values between -0.1°C and -0.6°C (Fig. 2). While temperature anomalies were variable at the surface, they became increasingly negative in the sub-surface ocean (Fig. 3), due to the shoaling of the thermocline across the east-central and eastern Pacific (Fig. 4). Though remaining mostly north of the equator, convection was suppressed over the western and central Pacific Ocean and slightly enhanced near Indonesia (Fig. 5). The low-level trade winds were stronger than average over a small region of the far western tropical Pacific Ocean, and upper-level winds were anomalously easterly over a small area of the east-central Pacific.  Overall, the ocean and atmosphere system remains consistent with ENSO-neutral.

A majority of the models in the IRI/CPC suite of Niño-3.4 predictions favor ENSO-neutral through the Northern Hemisphere 2017-18 winter (Fig. 6). However, the most recent predictions from the NCEP Climate Forecast System (CFSv2) and the North American Multi-Model Ensemble (NMME) indicate the formation of La Niña as soon as the Northern Hemisphere fall 2017 (Fig. 7).  Forecasters favor these predictions in part because of the recent cooling of surface and sub-surface temperature anomalies, and also because of the higher degree of forecast skill at this time of year.  In summary, there is an increasing chance (~55-60%) of La Niña during the Northern Hemisphere fall and winter 2017-18 (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA’s National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Forecasts are also updated monthly in the Forecast Forum section of CPC’s Climate Diagnostics Bulletin. Additional perspectives and analysis are also available in an ENSO blog.

The next ENSO Diagnostics Discussion is scheduled for 14 September 2017. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to: ncep.list.enso-update@noaa.gov.

Climate Prediction Center
National Centers for Environmental Prediction
NOAA/National Weather Service
College Park, MD 20740

CPC/IRI Early-Month Official ENSO Forecast Probabilities

Season La Niña Neutral El Niño
ASO 2017 42% 58% 0%
SON 2017 55% 44% 1%
OND 2017 61% 37% 2%
NDJ 2017 62% 35% 3%
DJF 2018 61% 36% 3%
JFM 2018 54% 42% 4%
FMA 2018 43% 51% 6%
MAM 2018 31% 60% 9%
AMJ 2018 26% 58% 16%

Please refer to our licensing agreement for permission to use IRI ENSO materials. The CPC/IRI materials are not included in this licensing.

IRI ENSO Forecast

IRI Technical ENSO Update

Published: August 18, 2017

Note: The SST anomalies cited below refer to the OISSTv2 SST data set, and not ERSSTv4. OISSTv2 is often used for real-time analysis and model initialization, while ERSSTv4 is used for retrospective official ENSO diagnosis because it is more homogeneous over time, allowing for more accurate comparisons among ENSO events that are years apart. During ENSO events, OISSTv2 often shows stronger anomalies than ERSSTv4, and during very strong events the two datasets may differ by as much as 0.5 C. Additionally, the ERSSTv4 may tend to be cooler than OISSTv2, because ERSSTv4 is expressed relative to a base period that is updated every 5 years, while the base period of OISSTv2 is updated every 10 years and so, half of the time, is based on a slightly older period and does not account as much for the slow warming trend in the tropical Pacific SST.

Recent and Current Conditions

In mid-August 2017, the NINO3.4 SST anomaly was in the middle of the ENSO-neutral category. For July the SST anomaly was 0.39 C, toward the warm side of ENSO-neutral, and for May-July it was 0.47 C, in the far upper part of the ENSO-neutral range. The IRI’s definition of El Niño, like NOAA/Climate Prediction Center’s, requires that the SST anomaly in the Nino3.4 region (5S-5N; 170W-120W) exceed 0.5 C. Similarly, for La Niña, the anomaly must be -0.5 C or less. The climatological probabilities for La Niña, neutral, and El Niño conditions vary seasonally, and are shown in a table at the bottom of this page for each 3-month season. The most recent weekly anomaly in the Nino3.4 region had cooled to -0.2, in the lower half of the ENSO-neutral range. The pertinent atmospheric variables, including the upper and lower level zonal wind anomalies, have been showing mainly neutral patterns. The Southern Oscillation Index (SOI) and the equatorial SOI have been near to somewhat above average. Subsurface temperature anomalies across the eastern equatorial Pacific have declined to become just slightly below average. The combination of the SST and the atmospheric conditions clearly warrants an ENSO-neutral diagnosis.

Expected Conditions

What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued approximately one week ago in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it stated that ENSO-neutral has the greatest chance of prevailing through fall and into winter, with markedly lower chances for El Niño or La Niña development. The latest set of model ENSO predictions, from mid-August, now available in the IRI/CPC ENSO prediction plume, is discussed below. Those predictions suggest that the SST has the greatest chance for being in the ENSO-neutral range for August-October through the rest of 2017, and show a likelihood of only 25% or less for El Niño development and for La Niña development through the period.

As of mid-August, at least 78% of the dynamical or statistical models predicts neutral ENSO conditions from the initial Aug-Oct 2017 season through the final Apr-Jun 2018 season. During this period, less than 10% of models predict El Niño conditions except for the final March-May and Apr-June 2018 seasons, when the percentage of models increases to about 20%. During this period, up to about 15% of models predict La Niña conditions, maximizing in the Dec-Feb season. At lead times of 3 or more months into the future, statistical and dynamical models that incorporate information about the ocean’s observed subsurface thermal structure generally exhibit higher predictive skill than those that do not. For the Nov-Jan 2017-18 season, among models that do use subsurface temperature information, 84% of models predicts neutral conditions, 11% predicts La Niña conditions, and 5% predicts El Niño conditions. These are similar percentages to those using all models, and the similarity persists also for longer lead target periods.

Note  – Only models that produce a new ENSO prediction every month are included in the above statement.

Caution is advised in interpreting the distribution of model predictions as the actual probabilities. At longer leads, the skill of the models degrades, and skill uncertainty must be convolved with the uncertainties from initial conditions and differing model physics, leading to more climatological probabilities in the long-lead ENSO Outlook than might be suggested by the suite of models. Furthermore, the expected skill of one model versus another has not been established using uniform validation procedures, which may cause a difference in the true probability distribution from that taken verbatim from the raw model predictions.

An alternative way to assess the probabilities of the three possible ENSO conditions is more quantitatively precise and less vulnerable to sampling errors than the categorical tallying method used above. This alternative method uses the mean of the predictions of all models on the plume, equally weighted, and constructs a standard error function centered on that mean. The standard error is Gaussian in shape, and has its width determined by an estimate of overall expected model skill for the season of the year and the lead time. Higher skill results in a relatively narrower error distribution, while low skill results in an error distribution with width approaching that of the historical observed distribution. This method shows probabilities for La Niña low throughout the forecast period, maximizing at about 25% during the Oct-Dec 2017 through Dec-Feb seasons. Similarly the chances for El Niño are low throughout, hovering just over 20% for fall 2017 and winter 2017-18, then rising to just over 30% by late spring 2018. Probabilities for ENSO-neutral are more than 80% for Aug-Oct, dropping to about 55% from Oct-Dec to Dec-Feb, and rising to about 65% for the final seasons of Feb-Apr through Apr-Jun 2018. Again, neutral is the clearly favored outcome.  A plot of the probabilities generated from this most recent IRI/CPC ENSO prediction plume using the multi-model mean and the Gaussian standard error method summarizes the model consensus out to about 10 months into the future. The same cautions mentioned above for the distributional count of model predictions apply to this Gaussian standard error method of inferring probabilities, due to differing model biases and skills. In particular, this approach considers only the mean of the predictions, and not the total range across the models, nor the ensemble range within individual models.

In summary, the probabilities derived from the models on the IRI/CPC plume describe, on average, a preference for ENSO-neutral throughout the forecast period, with chances for El Niño or La Niña less than one-half those for neutral throughout.  A caution regarding this latest set of model-based ENSO plume predictions, is that factors such as known specific model biases and recent changes that the models may have missed will be taken into account in the next official outlook to be generated and issued in early June by CPC and IRI, which will include some human judgement in combination with the model guidance.

Climatological Probabilities

Season La Niña Neutral El Niño
DJF 36% 30% 34%
JFM 34% 38% 28%
FMA 28% 49% 23%
MAM 23% 56% 21%
AMJ 21% 58% 21%
MJJ 21% 56% 23%
JJA 23% 54% 23%
JAS 25% 51% 24%
ASO 26% 47% 27%
SON 29% 39% 32%
OND 32% 33% 35%
NDJ 35% 29% 36%

 

Please refer to our licensing agreement for permission to use IRI ENSO materials. The CPC/IRI materials are not included in this licensing.

IRI ENSO Forecast

IRI/CPC Model-Based Probabilistic ENSO Forecast

Published: August 18, 2017

A purely objective ENSO probability forecast, based on regression, using as input the model predictions from the plume of dynamical and statistical forecasts shown in the ENSO Predictions Plume. Each of the forecasts is weighted equally. It is updated near or just after the middle of the month, using forecasts from the plume models that are run in the first half of the month. It does not use any human interpretation or judgment. This is updated on the third Thursday of the month.



IRI/CPC Mid-Month Model-Based ENSO Forecast Probabilities

Season La Niña Neutral El Niño
ASO 2017 9% 82% 9%
SON 2017 19% 65% 16%
OND 2017 24% 55% 21%
NDJ 2017 25% 54% 21%
DJF 2018 24% 55% 21%
JFM 2018 17% 61% 22%
FMA 2018 10% 67% 23%
MAM 2018 6% 68% 26%
AMJ 2018 5% 63% 32%

IRI ENSO Forecast

CPC/IRI Official Probabilistic ENSO Forecast

Published: September 14, 2017

The official CPC/IRI ENSO probability forecast, based on a consensus of CPC and IRI forecasters. It is updated during the first half of the month, in association with the official CPC/IRI ENSO Diagnostic Discussion. It is based on observational and predictive information from early in the month and from the previous month. It uses human judgment in addition to model output, while the forecast shown in the Model-Based Probabilistic ENSO Forecast relies solely on model output. This is updated on the second Thursday of every month.



CPC/IRI Early-Month Official ENSO Forecast Probabilities

Season La Niña Neutral El Niño
ASO 2017 42% 58% 0%
SON 2017 55% 44% 1%
OND 2017 61% 37% 2%
NDJ 2017 62% 35% 3%
DJF 2018 61% 36% 3%
JFM 2018 54% 42% 4%
FMA 2018 43% 51% 6%
MAM 2018 31% 60% 9%
AMJ 2018 26% 58% 16%

Please refer to our licensing agreement for permission to use IRI ENSO materials. The CPC/IRI materials are not included in this licensing.

IRI ENSO Forecast

IRI/CPC ENSO Predictions Plume

Published: August 18, 2017

Note on interpreting model forecasts

The following graph and table show forecasts made by dynamical and statistical models for SST in the Nino 3.4 region for nine overlapping 3-month periods. Note that the expected skills of the models, based on historical performance, are not equal to one another. The skills also generally decrease as the lead time increases. Thirdly, forecasts made at some times of the year generally have higher skill than forecasts made at other times of the year--namely, they are better when made between June and December than when they are made between February and May. Differences among the forecasts of the models reflect both differences in model design, and actual uncertainty in the forecast of the possible future SST scenario.


Because of occasional data corrections and late model runs following the time of ENSO product issuance, the data shown in the ENSO forecast table and the ENSO plume graph may not always match. The best source of the ENSO forecast data is http://iri.columbia.edu/~forecast/ensofcst/Data/ensofcst_ALLtoMMYY where MM is the month number and YY is the year.


Seasons (2017-2018)
Model ASO SON OND NDJ DJF JFM FMA MAM AMJ
Dynamical models
NASA GMAO model -0.4 -0.4 -0.3 -0.2 -0.1 0 0.1
NCEP CFS version 2 0.1 -0.1 -0.3 -0.4 -0.6 -0.7 -0.5 -0.1
Japan Met. Agency model -0.3 -0.3 -0.3 -0.4 -0.4
 Beijing Climae Center BCC-CSM1.1M 0.3 0.5 0.7 0.8 0.8 0.8 0.7 0.6 0.5
 King Abdulaziz University (Saudi Arabia) -0.1 -0.1 -0.1 -0.2 -0.1 0 0.2 0.4 0.4
Lamont-Doherty model 0.3 0.3 0.2 0.1 0.1 0.3 0.5 0.5 0.6
POAMA (Austr) model -0.2 -0.2 -0.1 -0.1 -0.2 -0.1 0
ECMWF model 0 0 0.1 0.2 0.2
UKMO model -0.5 -0.5 -0.4 -0.3
KMA (Korea) SNU model 0.2 0.3 0.3 0.4 0.3 0.3 0.3 0.2 0.1
IOCAS (China) Intermed. Coupled model 0 -0.1 -0.2 -0.2 -0.1 0 0.1 0.2 0.3
COLA CCSM4 model 0 -0.3 -0.5 -0.7 -0.7 -0.7 -0.5 -0.2 0
MÉTÉO FRANCE model -0.3 -0.5 -0.6 -0.6 -0.6
CSIR-IRI 3-model MME 0.2 0.2 0.1 0 -0.2 -0.3
GFDL CM2.1 Coupled Climate model -0.4 -0.6 -0.5 -0.4 -0.2 0 0.2 0.3 0.3
Canadian Coupled Fcst Sys 0.2 0.2 0.2 0.2 0.2 0.1 0.2 0.3 0.4
GFDL CM2.5 FLOR Coupled Climate model -0.2 -0.1 -0.1 0 0.1 0.2 0.4 0.5 0.7
Average, dynamical models -0.1 -0.1 -0.1 -0.1 -0.1 0 0.1 0.3 0.4
Statistical models
NCEP/CPC Markov model -0.1 -0.1 -0.1 0 0 0.1 0 0 0
NCEP/CPC Constructed Analog 0.5 0.5 0.5 0.5 0.4 0.3 0.2 0.1 0.1
Landsea/Knaff CLIPER 0.1 0.2 0.2 0.3 0.2 0.2 0.1 0.2 0.3
Univ. BC Neural Network -0.1 -0.3 -0.2 -0.2 -0.2 -0.1 0.1 0.2 0.2
FSU Regression 0.4 0.4 0.4 0.4 0.4 0.3 0.3 0.2 0.1
TCD – UCLA 0.3 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1
Average, statistical models 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.1
Average, all models 0 0 0 0 0 0 0.1 0.2 0.3

Discussion of Current Forecasts

Most of the models in the set of dynamical and statistical model predictions issued during early August 2017 predicts ENSO-neutral conditions during the forecast period of August-October 2017 to April-June 2018 period, although a minority predicts weak El Niño or weak La Niña during part of the period.  In the most recent week, the SST anomaly in the Nino3.4 region was -0.2 C, in the ENSO-neutral range, and 0.39 C for the month of July, also neutral but on the warm side.  The key atmospheric variables continue to reflect ENSO-neutral patterns.  Based on the multi-model mean prediction, and the expected skill of the models by start time and lead time, the probabilities (X100) for La Niña, neutral and El Niño conditions (using -0.5C and 0.5C thresholds) over the coming 9 seasons are:

IRI/CPC Mid-Month Model-Based ENSO Forecast Probabilities

Season La Niña Neutral El Niño
ASO 2017 9% 82% 9%
SON 2017 19% 65% 16%
OND 2017 24% 55% 21%
NDJ 2017 25% 54% 21%
DJF 2018 24% 55% 21%
JFM 2018 17% 61% 22%
FMA 2018 10% 67% 23%
MAM 2018 6% 68% 26%
AMJ 2018 5% 63% 32%

Summary of forecasts issued over last 22 months

The following plots show the model forecasts issued not only from the current month (as in the plot above), but also from the 21 months previous to this month. The observations are also shown up to the most recently completed 3-month period. The plots allow comparison of plumes from the previous start times, or examination of the forecast behavior of a given model over time. The first plot shows forecasts for dynamical models, the second for statistical models, and the third for all models. For less difficult readability, forecasts are shown to a maximum of only the first five lead times. Below the third plot, we provide a mechanism for highlighting the forecasts of one model at a time against a background of more lightly colored lines for all other models.


Notes on the data 

Only models producing forecasts on a monthly basis are included. This means that some models whose forecasts appear in the Experimental Long-Lead Forecast Bulletin (produced by COLA) do not appear in the table.

The SST anomaly forecasts are for the 3-month periods shown, and are for the Nino 3.4 region (120-170W, 5N-5S). Often, the anomalies are provided directly in a graph or a table by the respective forecasting centers for the Nino 3.4 region. In some cases, however, they are given for 1-month periods, for 3-month periods that skip some of the periods in the above table, and/or only for a region (or regions) other than Nino 3.4. In these cases, the following means are used to obtain the needed anomalies for the table:

  • Temporal averaging
  • Linear temporal interpolation
  • Visual averaging of values on a contoured map

The anomalies shown are those with respect to the base period used to define the normals, which vary among the groups producing model forecasts. They have not been adjusted to anomalies with respect to a common base period. Discrepancies among the climatological SST resulting from differing base periods may be as high as a quarter of a degree C in the worst cases. Forecasters are encouraged to use the standard 1971-2000 period as the base period, or a period not very different from it.

Please refer to our licensing agreement for permission to use IRI ENSO materials. The CPC/IRI materials are not included in this licensing.

IRI ENSO Forecast

IRI/CPC ENSO Prediction Plumes Based on the North American Multi-model Ensemble (NMME) + Other Comprehensive Dynamical Models

NMME+ Models not available yet for Sep, 2017