IRI ENSO Forecast

2019 September Quick Look

Published: September 19, 2019

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

SSTs in the east-central Pacific maintained ENSO-neutral levels during September. Patterns in the key atmospheric variables are also showing ENSO-neutral conditions. Model forecasts generally favor ENSO-neutral through autumn, winter and into spring, with slightly higher chances for El Niño than La Niña. The official CPC/IRI outlook is consistent with these model forecasts.

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.

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  Figure 1.

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  Figure 3.

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  Figure 2

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  Figure 4.

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 12, 2019

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: Not Active

Synopsis:

ENSO-neutral is favored during the Northern Hemisphere fall 2019 (~75% chance) and is expected to continue through Northern Hemisphere spring 2020 (55-60% chance).

During August, ENSO-neutral continued as reflected by the near-average sea surface temperatures (SST) across most of the central and eastern equatorial Pacific Ocean (Fig. 1). The latest weekly Niño-3 and Niño-3.4 values were -0.2°C and 0.0°C, respectively, with the westernmost Niño-4 region remaining above average (0.5°C) and the easternmost Niño-1+2 region remaining below average (-0.6°C; Fig. 2). Upper-ocean subsurface temperature anomalies (averaged across 180°-100°W) decreased slightly during the month (Fig. 3), with below-average temperatures strengthening in the east-central equatorial Pacific (Fig. 4). Suppressed tropical convection continued over parts of Indonesia, while near-average convection was evident near the Date Line (Fig. 5). Low-level and upper-level wind anomalies were near average over most of the tropical Pacific Ocean.  Overall, oceanic and atmospheric conditions were consistent with ENSO-neutral.

The majority of models in the IRI/CPC plume (Fig. 6) continue to favor ENSO-neutral (Niño-3.4 index between -0.5°C and +0.5°C) through the Northern Hemisphere spring.  However, the statistical model averages appear to favor Niño-3.4 values that are at the ElNiño thresholds (+0.5°C) during the fall and winter.  Forecasters are leaning toward the dynamical model average, which is also supported by the current tendency of the ocean toward cooler conditions.  In summary, ENSO-neutral is favored during the Northern Hemisphere fall 2019 (~75% chance) and is expected to continue through Northern Hemisphere spring 2020 (55-60% chance;  click the 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 10 October 2019. 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.

CPC/IRI Early-Month Official ENSO Forecast Probabilities

Season	La Niña	Neutral	El Niño
ASO 2019	5%	85%	10%
SON 2019	9%	74%	17%
OND 2019	12%	65%	23%
NDJ 2019	13%	59%	28%
DJF 2020	13%	58%	29%
JFM 2020	14%	57%	29%
FMA 2020	14%	57%	29%
MAM 2020	14%	58%	28%
AMJ 2020	14%	59%	27%

 

IRI ENSO Forecast

IRI Technical ENSO Update

Published: September 19, 2019

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-September 2019, coolish but neutral ENSO SST conditions were observed in the NINO3.4 region. The August SST anomaly was 0.20 C, in the neutral range, and for Jun-Aug it was 0.40 C, in the upper portion of the 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 was -0.3 C, in the lower portion of the ENSO-neutral range.  From October 2018 to June 2019 borderline or weak El Niño conditions prevailed in the tropical Pacific, and transitioned to neutral levels by July. SST anomalies have become slightly negative in the eastern equatorial Pacific, but remain above-average in the central and most of the western part of the basin. Atmospheric variables have also been neutral for the last couple of months, including low-level and upper-level zonal wind anomalies and the anomalous convection. Subsurface temperature anomalies from the dateline eastward in the equatorial Pacific have been near to just slightly below average during the last month, with strongest negative anomalies well east from the dateline.

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 states that the currently neutral conditions are most likely to continue through the fall, winter and spring. The latest set of model ENSO predictions, from mid-September, now available in the IRI/CPC ENSO prediction plume, is next discussed: As of mid-September, 12% of the dynamical or statistical models predict El Niño conditions for the Sep-Nov season, and 82% predict ENSO-neutral. Going forward, this large probability difference decreases, and from Nov-Jan through May-Jul 2020, about 55-70% predict neutral and 30-45% predict El Niño, leaving none predicting La Niña.

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 less than 10% for all forecast seasons. Probabilities for neutral conditions begin at 75% for Sep-Nov, and drop to 53-59% for Nov-Jan through May-Jul. Probabilities for El Niño begin at 23% for Sep-Nov and rise to near 40% from Nov-Jan through the final season of May-Jul 2020. 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 tilt of the odds toward neutral ENSO conditions for the entire forecast period of Sep-Nov through May-Jul 2020, with El Niño most competitive from Nov-Jan onward when it hovers near 40%. Probabilities for La Niña are no higher than 7% throughout the forecast period. 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 early next month by CPC and IRI, which will include some human judgment in combination with the model guidance.

IRI ENSO Forecast

IRI/CPC Model-Based Probabilistic ENSO Forecast

Published: September 19, 2019

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.

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

Season	La Niña	Neutral	El Niño
SON 2019	2%	75%	23%
OND 2019	4%	61%	35%
NDJ 2019	6%	56%	38%
DJF 2019	7%	53%	40%
JFM 2020	5%	55%	40%
FMA 2020	3%	56%	41%
MAM 2020	2%	59%	39%
AMJ 2020	3%	56%	41%
MJJ 2020	7%	54%	39%

 

IRI ENSO Forecast

CPC/IRI Official Probabilistic ENSO Forecast

Published: September 12, 2019

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.

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CPC/IRI Early-Month Official ENSO Forecast Probabilities

Season	La Niña	Neutral	El Niño
ASO 2019	5%	85%	10%
SON 2019	9%	74%	17%
OND 2019	12%	65%	23%
NDJ 2019	13%	59%	28%
DJF 2020	13%	58%	29%
JFM 2020	14%	57%	29%
FMA 2020	14%	57%	29%
MAM 2020	14%	58%	28%
AMJ 2020	14%	59%	27%

 

IRI ENSO Forecast

IRI/CPC ENSO Predictions Plume

Published: September 19, 2019

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.

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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.

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	Seasons (2019 – 2020)
Model	SON	OND	NDJ	DJF	JFM	FMA	MAM	AMJ	MJJ
Dynamical Models
NASA GMAO	-0.01	-0.04	-0.11	-0.28	-0.39	-0.31	-0.07
NCEP CFSv2	0.13	0.32	0.23	0.13	0.08	0.12	0.19	0.21
JMA	-0.2	-0.14	-0.17	-0.15	-0.07
BCC_CSM11m	-0.08	0.08	0.19	0.26	0.34	0.45	0.54	0.6	0.62
SAUDI-KAU	-0.36	-0.34	-0.25	-0.12	0.05	0.21	0.3	0.29	0.25
LDEO	0.35	0.39	0.52	0.71	0.86	0.84	0.68	0.47	0.2
AUS/ACCESS	0.47	0.53	0.53	0.6
ECMWF	0.24	0.38	0.35	0.27	0.23
UKMO	0.29	0.31	0.31	0.32
KMA SNU	-0.23	-0.2	-0.13	-0.08	-0.07	-0.07	-0.09	-0.08	-0.07
IOCAS ICM	0.24	0.38	0.41	0.34	0.26	0.21	0.19	0.17	0.14
COLA CCSM4	0.13	0.13	0.02	0.02	0.14	0.32	0.48	0.51	0.46
MetFRANCE	0.39	0.63	0.73	0.77	0.79
SINTEX-F	0.33	0.52	0.64	0.71	0.69	0.64	0.62	0.6	0.57
CS-IRI-MM	0.44	0.59	0.65	0.68	0.71	0.74
GFDL CM2.1	0.45	0.66	0.74	0.75	0.74	0.8	0.85	0.87	0.8
CMC CANSIP	-0.03	0	0	0.07	0.14	0.19	0.17	0.15	0.1
GFDL FLOR	0.32	0.39	0.42	0.51	0.65	0.8	0.9	0.92	0.91
Average, Dynamical Models	0.16	0.26	0.28	0.31	0.32	0.38	0.40	0.43	0.40
Statistical Models
NTU CODA	0.6	0.6	0.58	0.55	0.53	0.49	0.47
BCC_RZDM	-0.09	-0.17	-0.21	-0.22	-0.19	-0.14	-0.12	-0.08	-0.05
CPC MRKOV	0.17	0.29	0.42	0.51	0.53	0.48	0.45	0.46	0.46
CPC CA	0.61	0.73	0.73	0.59	0.46	0.41	0.35	0.32	0.25
CSU CLIPR	0.49	0.4	0.3	0.21	0.26	0.3	0.35	0.23	0.1
IAP-NN	0.73	0.84	0.93	0.98	1.04	1.08	1.12	1.13	1.13
UBC NNET	0.44	0.56	0.55	0.54	0.53	0.49	0.46	0.42	0.35
FSU REGR	0.28	0.34	0.36	0.32	0.23	0.1	-0.08	-0.25	-0.39
UCLA-TCD	0.26	0.32	0.38	0.42	0.45	0.47	0.47	0.47	0.47
Average, Statistical Models	0.39	0.43	0.45	0.43	0.43	0.41	0.39	0.34	0.29

Discussion of Current Forecasts

Many of the models in the set of dynamical and statistical model predictions issued during mid-September 2019 show currently slightly below-average but ENSO-neutral conditions warming to slightly above-average but neutral conditions into the fall, winter and into spring. A few models show weak El Niño conditions redeveloping during fall and extending into winter and spring. No model predicts La Niña development. In the most recent week, the SST anomaly in the Nino3.4 region was -0.3 C, in the lower portion of the ENSO-neutral range, and 0.20 C for the month of August, in the ENSO-neutral category. The subsurface sea temperature anomalies have dropped to very slightly below average. About 85-90% of the dynamical and statistical models predict neutral conditions for the Sep-Nov season, and objective model-based probabilities are 75% for neutral for Sep-Nov, dropping to about 55-60% by winter as probabilities for El Niño slowly rise to near 40% from early winter through spring. 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
SON 2019	2%	75%	23%
OND 2019	4%	61%	35%
NDJ 2019	6%	56%	38%
DJF 2019	7%	53%	40%
JFM 2020	5%	55%	40%
FMA 2020	3%	56%	41%
MAM 2020	2%	59%	39%
AMJ 2020	3%	56%	41%
MJJ 2020	7%	54%	39%

 

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.

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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.

IRI ENSO Forecast

Forecast Probability Distribution Based on the IRI/CPC ENSO Prediction Plume

Models not available yet for Sep, 2019