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IRI ENSO Forecast

2015 August Quick Look

Published: August 20, 2015

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

During late July through early-August 2015 the SST was at a strong El Niño level. All atmospheric variables support the El Niño pattern, including weakened trade winds and excess rainfall in the east-central tropical Pacific. The consensus of ENSO prediction models indicate continuation of strong El Niño conditions during the August-October 2015 season in progress. Some further strengthening into fall is likely, with the event lasting into spring 2016.

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 Dec-Feb
  • Typically persist for 9-12 months, though occasionally persisting for up to 2 years
  • Typically recur every 2 to 7 years

Figure 1 is based on a consensus of CPC and IRI forecasters, in association with the official CPC/IRI ENSO Diagnostic Discussion

Figure 3 is purely objective, based on regression, using equally weighted model predictions from the plume

IRI ENSO Forecast

CPC/IRI ENSO Update

Published: August 13, 2015

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 Advisory

Synopsis: There is a greater than 90% chance that El Niño will continue through Northern Hemisphere winter 2015-16, and around an 85% chance it will last into early spring 2016.

During July, sea surface temperatures (SST) anomalies were near +1.0°C in the central equatorial Pacific Ocean, and in excess of +2.0°C across the eastern Pacific (Fig. 1). SST anomalies increased in the Niño-3 and Niño-3.4 regions, while the Niño-4 and Niño-1+2 indices decreased slightly during the month (Fig. 2).  Positive subsurface temperature anomalies strengthened in the central and east-central equatorial Pacific during the month  (Fig. 3), in association with the eastward movement of a downwelling oceanic Kelvin wave (Fig. 4). The atmosphere remained coupled to the oceanic warming, with significant low-level westerly wind anomalies continuing from the western to east-central equatorial Pacific, along with anomalous upper-level easterly winds. Also, the traditional and equatorial Southern Oscillation Index (SOI) were both negative, consistent with enhanced convection over the central and eastern equatorial Pacific and suppressed convection over Indonesia (Fig. 5). Collectively, these atmospheric and oceanic features reflect a significant and strengthening El Niño.

All models surveyed predict El Niño to continue into the Northern Hemisphere spring 2016, and all multi-model averages predict a strong event at its peak in late fall/early winter (3-month values of the Niño-3.4 index of +1.5°C or greater; Fig. 6). At this time, the forecaster consensus unanimously favors a strong El Niño, with peak 3-month SST departures in the Nino 3.4 region potentially near or exceeding +2.0°C. Overall, there is a greater than 90% chance that El Niño will continue through Northern Hemisphere winter 2015-16, and around an 85% chance it will last into early spring 2016 (click CPC/IRI consensus forecast for the chance of each outcome).

Across the contiguous United States, temperature and precipitation impacts associated with El Niño are expected to remain minimal during the remainder of the Northern Hemisphere summer and increase into the late fall and winter (the 3-month seasonal outlook will be updated on Thursday August 20th). El Niño will likely contribute to a below normal Atlantic hurricane season, and to above-normal hurricane seasons in both the central and eastern Pacific hurricane basins (click Hurricane season outlook for more).

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 September 2015. 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 Consensus ENSO Forecast Probabilities

 

Season La Niña Neutral El Niño
JAS 2015 ~0% ~0% 100%
ASO 2015 ~0% 1% 99%
SON 2015 ~0% 1% 99%
OND 2015 ~0% 1% 99%
NDJ 2015 ~0% 2% 98%
DJF 2015 ~0% 5% 95%
JFM 2016 1% 7% 92%
FMA 2016 2% 13% 85%
MAM 2016 2% 28% 70%

IRI ENSO Forecast

IRI Technical ENSO Update

Published: August 20, 2015

Recent and Current Conditions

The SST anomaly in the NINO3.4 region attained a weak El Niño level beginning late February 2015, strengthened to moderate strength around mid-May, and strengthened further to a strong level beginning around mid-July. For July the average NINO3.4 SST anomaly was 1.60 C, indicative of strong El Niño conditions, and for May-July it was 1.32 C. 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 SST anomaly in the Nino3.4 region was 2.0 C, in the category of strong El Niño. Accompanying this SST has been an El Niño atmospheric pattern, including westerly low-level wind anomalies and positive anomalies of convection near and east of the dateline. The Southern Oscillation Index (SOI) and the equatorial SOI have also been quite negative, indicative of El Niño conditions.

Expected Conditions

What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued one week ago in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it called for a greater than 90% likelihood for El Niño conditions continuing through winter 2015-16, and 85% to last into spring 2016. The latest set of model ENSO predictions, from mid-Aug, now available in the IRI/CPC ENSO prediction plume, is discussed below. Currently, weekly Nino3.4 SST anomalies are in the stromg El Niño cagtegory. Subsurface temperature anomalies across the eastern equatorial Pacific have been well above average levels during the past 5 months as the downwelling phases of several Kelvin waves (one in the earlier months this year, and several more following that) have moved eastward at depth in response to westerly low-level wind anomalies over the course of the last 5 months. The strong positive heat content anomaly has promoted steady increases in SST over the last 3 months, and is likely to lead to still further SST increases in the coming months, depending on the strength and nature of the atmospheric-oceanic feedbacks. In the atmosphere, the basin-wide sea level pressure anomaly pattern (e.g. the SOI) has been decidedly at El Niño levels.  Anomalous convection (as measured by OLR) has been above average both near and to the east of the dateline.  Together, the oceanic and atmospheric features reflect strong El Niño conditions for late July through mid-August.

As of mid-August, none of the dynamical or statistical models models predicts La Niña or neutral SST conditions for the initial Aug-Oct 2015 season; 100% predicts El Niño conditions. 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 2015-16 season, among models that do use subsurface temperature information, 100% predicts El Niño SST conditions, while none predicts ENSO-neutral conditions and none predicts La Niña conditions. For all model types, the probabilities for El Niño are near 100% (i.e., higher than 99.5%) for Aug-Oct through Feb-Apr 2016, dropping to 89% for Mar-May and 78% for Apr-Jun. No models predict La Niña conditions for any forecast period during 2015 and early 2016. Chances for neutral ENSO conditions are near 0% through Feb-Apr 2016, 11% for Mar-May and 22% for Apr-Jun 2016.

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 near-zero from Aug-Oct through Mar-May 2016, and 1% for Apr-Jun 2016.  Model probabilities for neutral ENSO conditions are 5% or less through Feb-Apr 2016, 9% for Mar-May and 30% for Apr-Jun 2016. Probabilities for El Niño are near 100% for Aug-Oct 2015 to Nov-Jan 2015-16, 99% for Dec-Feb and Jan-Mar 2016, 98% down to 90% for Feb-Apr and Mar-May 2016 respectively, and 69% for Apr-Jun 2016.  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.

The probabilities derived from the models on the IRI/CPC plume describe, on average, extremely high certainty for El Niño conditions for the Aug-Oct 2015 through Jan-Mar 2016 seasons, and still very high certainty through Feb-Apr 2016. In terms of magnitude, the models suggest strengthening El Niño conditions through northern autumn season, most likely peaking at the level of strong El Niño. Model forecast spread still exists, and peak event strength could range from about 1.5 to 2.5 C with a slight possibility of being outside of that interval on either side. 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 March 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%

 

IRI ENSO Forecast

IRI/CPC Plume-Based Probabilistic ENSO Forecast

Published: August 20, 2015



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

Season La Niña Neutral El Niño
ASO 2015 ~0% ~0% 100%
SON 2015 ~0% ~0% 100%
OND 2015 ~0% ~0% 100%
NDJ 2015 ~0% ~0% 100%
DJF 2015 ~0% 1% 99%
JFM 2016 ~0% 1% 99%
FMA 2016 ~0% 2% 98%
MAM 2016 ~0% 9% 91%
AMJ 2016 1% 30% 69%

IRI ENSO Forecast

CPC/IRI Consensus Probabilistic ENSO Forecast

Published: August 13, 2015



CPC/IRI Early-Month Consensus ENSO Forecast Probabilities

 

Season La Niña Neutral El Niño
JAS 2015 ~0% ~0% 100%
ASO 2015 ~0% 1% 99%
SON 2015 ~0% 1% 99%
OND 2015 ~0% 1% 99%
NDJ 2015 ~0% 2% 98%
DJF 2015 ~0% 5% 95%
JFM 2016 1% 7% 92%
FMA 2016 2% 13% 85%
MAM 2016 2% 28% 70%

IRI ENSO Forecast

IRI/CPC ENSO Predictions Plume

Published: August 20, 2015

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.


Seasons (2015-2016)
Model ASO SON OND NDJ DJF JFM FMA MAM AMJ
Dynamical models
NCEP CFS version 2 2.1 2.5 2.7 2.4 2 1.6 1.3 0.9
NASA GMAO model 2.8 3.1 3.3 3.5 3.6 3.4 3
Japan Met. Agency model 2 2.2 2.4 2.3 2
Scripps Inst. HCM 1.5 1.7 1.9 2 2 1.8 1.5 1 0.6
Lamont-Doherty model 2.1 2.3 2.4 2.4 2.3 1.9 1.4 0.9 0.5
POAMA (Austr) model 2.3 2.5 2.5 2.5 2.3 1.9 1.5
ECMWF model 2.4 2.7 3 3 2.8
UKMO model 2.4 2.6 2.6 2.6
KMA (Korea) SNU model 1.8 1.8 1.7 1.6 1.4 1.3 1.1 1 0.8
IOCAS (China) Intermed. Coupled model 1.9 2 2.1 2.2 2 1.7 1.2 0.7 0.3
COLA CCSM3 model 2.3 2.5 2.6 2.9 2.9 2.7 2.1 1.5 0.8
MÉTÉO FRANCE model 2.9 3 2.9 2.6 2.1
Japan Frontier Coupled model 2.5 2.5 2.5 2.4 2.3 2.2 1.9 1.7 1.3
CSIR-IRI 3-model MME 1.3 1.6 1.9 1.9 1.6 1.2
GFDL CM2.1 Coupled Climate model 2.4 2.6 2.6 2.6 2.4 2.2 1.8 1.4 1
Canadian Coupled Fcst Sys 2.6 2.8 2.9 2.9 2.7 2.3 1.8 1.3 0.6
2.1 2.2 2.2 2.2 2.2 1.9 1.6 1.2 0.7
Average, dynamical models 2.2 2.4 2.5 2.5 2.3 2 1.7 1.2 0.7
Statistical models
NCEP/CPC Markov model 2.2 2.4 2.6 2.7 2.6 2.3 2 1.6 1.3
NOAA/CDC Linear Inverse 1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3
NCEP/CPC Constructed Analog 1.6 2 2.4 2.6 2.5 2.1 1.7 1.2 0.7
NCEP/CPC Can Cor Anal 1.1 1.1 1.2 1.2 0.9 0.7 0.5 0.4 0.2
Landsea/Knaff CLIPER 2 2.3 2.6 2.9 2.4 1.9 1.4 1 0.6
Univ. BC Neural Network 1.6 1.6 1.6 1.6 1.5 1.4 1.3 1.2 0.9
FSU Regression 1.7 1.9 2.1 2.2 2.1 1.7 1.3 0.9 0.5
TCD – UCLA 2.1 2.3 2.5 2.6 2.6 2.4 2.2 1.9 1.6
UNB/CWC Nonlinear PCA 1.6 1.4 1.2 0.9 0.7 0.6 0.6 0.5 0.5
Average, statistical models 1.6 1.8 1.9 1.9 1.8 1.5 1.3 1 0.7
Average, all models 2 2.2 2.3 2.3 2.1 1.8 1.5 1.1 0.7

Discussion of Current Forecasts

Most of the set of dynamical and statistical model predictions issued during late July and early August 2015 predict further strengthening El Niño SST conditions into fall 2015, with El Niño continuing throughout 2015 and into early 2016. Continuation of El Niño conditions appears at least 98% likely from the current Jul-Sep 2015 season through to the Feb-Apr 2015-16 season. The average of all models predicts El Niño amplification to strong levels (the level that has already now been attained), with very few predicting weakening from current levels. El Niño probabilities remain over 90% into spring 2016, and fall rapidly by Apr-June 2016. There is still spread among the individual model predictions, dynamical models showing  stronger El Niño predictions than statistical ones. Many models predict peak SST anomaly values between 1.5 and 2.5C, although some are outside of that interval on either side. In the most recent week, the SST anomaly in the Nino3.4 region was 2.0 C, reflecting strong El Niño conditions in this weekly time scale, and 1.6 C for the month of July, also at a minimally strong level.  Most of the atmospheric variables also reflect El Niño, including lower and upper level wind anomalies, and the pattern of anomalous convection. Based on the multi-model mean predictions, 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 Plume-Based ENSO Forecast Probabilities

Season La Niña Neutral El Niño
ASO 2015 ~0% ~0% 100%
SON 2015 ~0% ~0% 100%
OND 2015 ~0% ~0% 100%
NDJ 2015 ~0% ~0% 100%
DJF 2015 ~0% 1% 99%
JFM 2016 ~0% 1% 99%
FMA 2016 ~0% 2% 98%
MAM 2016 ~0% 9% 91%
AMJ 2016 1% 30% 69%

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.