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IRI ENSO Forecast

2018 September Quick Look

Published: September 19, 2018

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 2018, the east-central tropical Pacific waters reflected ENSO-neutral conditions, with near to slightly above-average SST. The key atmospheric variables also suggested neutral conditions, although weakly westerly low-level wind anomalies have developed. The subsurface water temperature continued to be above-average. The official CPC/IRI outlook calls for a 50-55% chance of El Niño development during fall, rising to 65-70% for winter 2018-19. An El Niño watch is in effect. The latest forecasts of statistical and dynamical models collectively favor El Niño development during fall, most likely maintaining weak strength during late fall and winter; most forecasters agree with this scenario.

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 13, 2018

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: El Niño Watch

Synopsis: There is a 50-55% chance of El Niño onset during the Northern Hemisphere fall 2018 (September-November), increasing to 65-70% during winter 2018-19.

ENSO-neutral continued during August, as indicated by a blend of slightly above- and below- average sea surface temperatures (SSTs) across the equatorial Pacific Ocean (Fig. 1). Over the last month, the westernmost Niño-4 region was the warmest (latest weekly value was +0.5°C), while the Niño-3 and Niño-3.4 regions were weakly positive, with Niño1+2 remaining negative (Fig. 2). Subsurface temperature anomalies (averaged across 180°-100°W) were positive (Fig. 3), with an increase in above-average subsurface temperatures in the central Pacific and slight expansion of negative anomalies in the eastern Pacific (Fig. 4). Convection returned to near average over the Date Line, and was slightly enhanced over Indonesia (Fig. 5). Low-level westerly wind anomalies re-developed across the east-central and western Pacific, although they were only slightly evident in the monthly average. Upper-level wind anomalies were westerly over the eastern Pacific. Overall, the oceanic and atmospheric conditions reflected ENSO-neutral.

The majority of models in the IRI/CPC plume continue to predict the onset of El Niño sometime during the Northern Hemisphere fall and continuing through the winter (Fig. 6). The forecasters also favor El Niño formation during the fall, and are leaning toward the more conservative model guidance that indicates a weak El Niño event. The persistence of above-average subsurface temperatures and continuing flare-ups of westerly wind anomalies also support the eventual development of El Niño.In summary, there is a 50-55% chance of El Niño onset during the Northern Hemisphere fall 2018 (September-November), increasing to 65-70% during winter 2018-19 (see 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 11 October 2018. 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 2018 0% 66% 34%
SON 2018 1% 47% 52%
OND 2018 1% 37% 62%
NDJ 2018 1% 33% 66%
DJF 2018 2% 31% 67%
JFM 2018 2% 34% 64%
FMA 2019 2% 39% 59%
MAM 2019 3% 45% 52%
AMJ 2019 5% 49% 46%

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: September 19, 2018

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 2018, the NINO3.4 SST anomaly showed neutral ENSO conditions. For August the SST anomaly was 0.30 C, indicating neutral conditions, and for Jun-Aug it was 0.27 C, also neutral. 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, showing neutral conditions. Additionally, most of the key atmospheric variables, including the upper level zonal wind anomalies, the outgoing longwave radiation pattern (convection), and the Southern Oscillation Index suggest neutral conditions over recent weeks. However, during the most recent month the low-level zonal wind anomalies have become weakly westerly, suggesting a tendency toward El Niño conditions. The subsurface temperature anomalies across the eastern equatorial Pacific remain at moderately above-average, and have recently shown a slight further increase. These warmed waters at depth have been impacting the surface, resulting in slightly above-average temperatures, and also presaging likely further warming of the SST in the coming months. Given the current and recent SST anomalies, the subsurface profile and the conditions of most key atmospheric variables, we see a likely warming to at least weak El Niño conditions beginning in the Sep-Nov period.

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 gave a 50-55% chance for El Niño development during fall season, rising to 65-70% for winter 2018-19. An El Niño watch remains active. The latest set of model ENSO predictions, from mid-September, now available in the IRI/CPC ENSO prediction plume, is discussed below.

As of mid-September, about 60-65% of the dynamical or statistical models predict El Niño conditions for the initial Sep-Nov 2018 season, with about 35-40% showing neutral conditions. Following that first forecast season, probabilities for neutral drop to roughly the 15-30% range for Oct-Dec 2018 through May-Jul 2019. Meanwhile, the probability for El Niño rises to 80-85% for Oct-Dec through Dec-Feb, but remains at more than 70% through to the final forecast season of May-Jul 2019. This hints at the possibility of a 2-year El Niño period, given the late start to the predicted 2018-19 El Niño. La Niña probabilities are near zero throughout the forecast period. 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 Dec-Feb 2018-19 season, among models that do use subsurface temperature information, 23% of models predicts neutral conditions and 77% predict El Niño conditions.

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 at 2% or less for the full range of seasons from Sep-Nov 2018 through to May-Jul 2019. Probabilities for neutral conditions begin at 45% for Sep-Nov, fall to about 25-30% for Nov-Jan through Apr-Jun, and are 36% for May-Jul. Probabilities for El Niño, which begin at 55% for Sep-Nov, rise to about the 70-75% range from Nov-Jan through Apr-Jun and drop to 62% for May-Jul. 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 a tilt of the odds toward El Niño conditions starting from Sep-Nov and continuing through May-Jul 2019, peaking around 70-75% from Nov-Jan through Apr-Jun. The predicted continuation of elevated chances for  El Niño well into spring/early summer 2019 hints at the possibility of a two-year El Niño episode, likely related to the late predicted onset of El Niño in 2018. Probabilities for La Niña are less than 5% throughout the entire 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.

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: September 19, 2018

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
SON 2018 0% 45% 55%
OND 2018 1% 31% 68%
NDJ 2018 1% 27% 72%
DJF 2018 1% 27% 72%
JFM 2019 1% 27% 72%
FMA 2019 0% 26% 74%
MAM 2019 0% 24% 76%
AMJ 2019 0% 29% 71%
MJJ 2019 2% 36% 62%

 

IRI ENSO Forecast

CPC/IRI Official Probabilistic ENSO Forecast

Published: September 13, 2018

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 2018 0% 66% 34%
SON 2018 1% 47% 52%
OND 2018 1% 37% 62%
NDJ 2018 1% 33% 66%
DJF 2018 2% 31% 67%
JFM 2018 2% 34% 64%
FMA 2019 2% 39% 59%
MAM 2019 3% 45% 52%
AMJ 2019 5% 49% 46%

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: September 19, 2018

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 (2018 – 2019)
Model SON OND NDJ DJF JFM FMA MAM AMJ MJJ
Dynamical Models
NASA GMAO 0.4 0.56 0.59 0.5 0.37 0.28 0.26
NCEP CFSv2 0.71 1.03 1.09 1.02 1 1.07 1.08 1.02
JMA 0.41 0.59 0.65 0.68 0.67
BCC_CSM11m 0.88 1.15 1.31 1.31 1.21 1.07 0.9 0.73 0.58
SAUDI-KAU 0.64 0.88 1.05 1.16 1.2 1.13 0.94 0.69 0.43
LDEO 0.48 0.5 0.44 0.37 0.35 0.37 0.36 0.29 0.2
AUS/POAMA 0.37 0.42 0.44 0.45 0.47 0.47 0.44
ECMWF 0.54 0.66 0.71 0.68 0.68
UKMO 0.62 0.75 0.85 0.9
KMA SNU 0.86 1.16 1.32 1.38 1.4 1.38 1.29 1.18 1.1
IOCAS ICM 0.39 0.47 0.52 0.44 0.29 0.16 0.09 0.05 0.01
COLA CCSM4 0.8 0.86 0.83 0.87 0.96 1 1.04 1.03 1.03
MetFRANCE 0.35 0.44 0.44 0.42 0.39
SINTEX-F 0.71 0.92 1.05 1.13 1.16 1.13 1.07 0.98 0.93
CS-IRI-MM 0.47 0.73 0.7 0.47 0.2 0.16
GFDL CM2.1 0.51 0.77 0.95 1.06 1.1 1.08 1.01 1.02 1.06
CMC CANSIP 0.52 0.6 0.66 0.73 0.69 0.7 0.65 0.63 0.64
GFDL FLOR 0.48 0.7 0.85 0.95 1.08 1.14 1.1 0.97 0.83
Average, Dynamical Models 0.56 0.73 0.80 0.81 0.78 0.80 0.79 0.78 0.68
Statistical Models
PSD-CU LIM 0.51 0.6 0.69 0.76 0.8 0.79 0.75 0.71 0.66
NTU CODA 0.1 0.6 0.86 1.3 1.11 0.94 1.02
CPC MRKOV 0.78 1.04 1.26 1.4 1.41 1.31 1.22 1.16 1.1
CPC CA 0.78 1.04 1.12 1.01 0.82 0.7 0.59 0.54 0.44
CSU CLIPR 0.57 0.58 0.59 0.6 0.51 0.43 0.34 0.22 0.1
UBC NNET 0.59 0.74 0.84 0.93 1.03 1.07 1.1 1.14 1.11
FSU REGR 0.5 0.69 0.8 0.82 0.72 0.63 0.63 0.7 0.74
UCLA-TCD 0.33 0.4 0.47 0.53 0.58 0.62 0.64 0.66 0.68
Average, Statistical Models 0.52 0.71 0.83 0.92 0.87 0.81 0.79 0.73 0.69

Discussion of Current Forecasts

Most of the models in the set of dynamical and statistical model predictions issued during mid-September 2018 indicate weak El Niño conditions from the Sep-Nov season and during winter 2018-19. In the most recent week, the SST anomaly in the Nino3.4 region was 0.3 C, in the neutral range, and 0.30 C for the month of July, also at a neutral level. All of the key atmospheric variables now reflect neutral conditions, although weak low-level westerly wind anomalies have appeared over the last month. The subsurface sea temperature anomalies continue to be moderately positive. More than 80% of the dynamical and statistical models predict El Niño conditions by the last quarter of 2018, and objective model-based probabilities are about 70-75%, including into the winter season. Forecasters accept this outlook, but temper the probability of El Niño to 65-70%. 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 2018 0% 45% 55%
OND 2018 1% 31% 68%
NDJ 2018 1% 27% 72%
DJF 2018 1% 27% 72%
JFM 2019 1% 27% 72%
FMA 2019 0% 26% 74%
MAM 2019 0% 24% 76%
AMJ 2019 0% 29% 71%
MJJ 2019 2% 36% 62%

 

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

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

Models not available yet for Sep, 2018