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IRI ENSO Forecast

2014 October Quick Look

Published: October 16, 2014

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)

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During September through early October the observed ENSO conditions retreated from those of a borderline El Niño to a warmish ENSO-neutral state. However, most of the ENSO prediction models continue to indicate development of weak El Niño conditions during the October-December season in progress, peaking at weak strength during winter 2014-15 and lasting through most of northern spring 2015.

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: October 9, 2014

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: El Niño is favored to begin in the next 1-2 months and last into the Northern Hemisphere spring 2015.

During September 2014, above-average sea surface temperatures (SST) continued across much of the equatorial Pacific (Fig. 1). The weekly Niño indices were relatively unchanged from the beginning of the month, with values ranging from +0.3°C (Niño-3.4) to +1.1°C (Niño-1+2) at the end of the month (Fig. 2). The change in subsurface heat content anomalies (averaged between 180º-100ºW) was also minimal (Fig. 3) due to the persistence of above-average temperatures at depth across the central and eastern Pacific (Fig. 4). Equatorial low-level winds were largely near average for the month, though brief periods of westerly wind anomalies continue to arise. Upper-level winds were also close to average for the month. The Southern Oscillation Index has remained negative, and rainfall was near average around the Date Line, with a mix of positive and negative anomalies over Indonesia and Papua New Guinea (Fig. 5). The lack of coherent atmospheric and oceanic features indicates the continuation of ENSO-neutral.

Most models predict El Niño to develop during October-December 2014 and to continue into early 2015 (Fig. 6). The consensus of forecasters indicates a 2-in-3 chance of El Niño during the November 2014 – January 2015 season. This El Niño will likely remain weak (3-month values of the Niño-3.4 index between 0.5°C and 0.9°C) throughout its duration. In summary, El Niño is favored to begin in the next 1-2 months and last into the Northern Hemisphere spring 2015 (click CPC/IRI consensus forecast for the chance of each outcome).

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 6 November 2014. 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 Consensus ENSO Forecast Probabilities

Season La Niña Neutral El Niño
SON 2014 ~0% 49% 51%
OND 2014 ~0% 38% 62%
NDJ 2014 1% 32% 67%
DJF 2014 1% 34% 65%
JFM 2015 1% 36% 63%
FMA 2015 2% 40% 58%
MAM 2015 3% 45% 52%
AMJ 2015 5% 47% 48%
MJJ 2015 8% 49% 43%

IRI ENSO Forecast

IRI Technical ENSO Update

Published: October 16, 2014

Recent and Current Conditions

The SST anomaly in the NINO3.4 region in recent weeks has slightly retreated from a borderline El Niño level, after having briefly reached that level around mid-September. For September the average NINO3.4 SST anomaly was 0.45 C, indicative of warm but still neutral conditions, and for Jul-Sep it was 0.28 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 0.4 C, very near the 0.45 C observed in September. Although the SST had been near the borderline of weak El Niño conditions in May and June, the atmospheric participation in an El Niño-like pattern had been weak or absent. Around mid-September, both ocean and atmosphere were suggestive of borderline or weak El Niño conditions, but that situation failed to lead to a sustained weak El Niño event, and current conditions fall short of the required thresholds both in the ocean and in the overlying atmosphere.

Expected Conditions

What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued earlier this month in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it called for a likelihood for a transition from neutral ENSO conditions to El Niño conditions during the fall of 2014 now in progress, with probabilities of El Niño rising to 67% for Nov-Jan 2014-15. The latest set of model ENSO predictions, from mid-October, now available in the IRI/CPC ENSO prediction plume, is discussed below. Currently, Nino3.4 SST anomalies are just short of the borderline 0.5C threshold for weak El Niño after having reached that level for a couple of weeks in mid-September. Subsurface temperature anomalies across the eastern equatorial Pacific have remained somewhat above average during the last month. In the atmosphere, the basin-wide sea level pressure pattern (e.g. the SOI) was around the borderline of weak Niño in mid-September but has recently weakened to the neutral range. Weak anomalous low-level westerlies have appeared at times during September and early October but have not been sustained. Upper level anomalous westerlies have also been observed during some periods over the last couple of months, but are currently weak. Anomalous convection (as measured by OLR) has been near average near and eastward of the dateline, and slightly suppressed in some portions of the area west of the dateline while enhanced in some small portions of the far western tropical Pacific.  Together, the oceanic and atmospheric features currently reflect a warmish but neutral ENSO condition.

As of mid-October, none of the dynamical or statistical models models predicts La Niña SST conditions for the initial Oct-Dec 2014 season, 70% predicts El Niño conditions, and 30% indicates neutral ENSO. 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 Jan-Mar 2015 season, among models that do use subsurface temperature information, 26% predicts ENSO-neutral SSTs, 74% predicts El Niño conditions and none predicts La Niña conditions. For all model types, the probability for neutral ENSO conditions is 30% or below between Oct-Dec 2014 and Apr-Jun 2015. Probabilities for El Niño rise to 70% or higher between these same two seasons, peaking at 79% for Mar-May 2015. No model predicts La Niña conditions for any of the 3-month periods between Oct-Dec 2014 and Jun-Aug 2015.

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 near 0% from Oct-Dec 2014 through Apr-Jun 2015, rising to 8% by Jun-Aug.  Model probabilities for neutral ENSO conditions are 35% for the initial period of Oct-Dec 2014, 34% for the next running period of Nov-Jan, reach a low of 33% for Dec-Feb 2014-15 through Feb-Apr 2015 and rise to 44% by Jun-Aug 2015. Probabilities for El Niño are 65% for Oct-Dec 2014, rise to 67% for Dec-Feb 2014-15 through Feb-Apr 2015, and decline to 48% for Jun-Aug 2015. The models collectively favor El Niño over other ENSO conditions by a sizable margin between Oct-Dec 2014 and Apr-Jun 2015.   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, a likely development of El Niño development during the Oct-Dec 2014 season currently in progress, enduring well into northern spring season of 2015. The consensus of model predictions calls for a weak El Niño event, although a moderate event or no event are also possible. A strong event appears very unlikely. 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 October 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 37% 28% 35%
JFM 34% 37% 29%
FMA 30% 48% 22%
MAM 26% 54% 20%
AMJ 24% 54% 22%
MJJ 25% 51% 24%
JJA 25% 50% 25%
JAS 27% 46% 27%
ASO 29% 40% 31%
SON 32% 34% 34%
OND 34% 31% 35%
NDJ 37% 27% 36%

 

IRI ENSO Forecast

IRI/CPC Plume-Based Probabilistic ENSO Forecast

Published: October 16, 2014



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

Season La Niña Neutral El Niño
OND 2014 ~0% 35% 65%
NDJ 2014 ~0% 34% 66%
DJF 2014 ~0% 33% 67%
JFM 2015 ~0% 33% 67%
FMA 2015 ~0% 33% 67%
MAM 2015 ~0% 35% 65%
AMJ 2015 ~0% 39% 61%
MJJ 2015 3% 42% 55%
JJA 2015 8% 44% 48%

IRI ENSO Forecast

CPC/IRI Consensus Probabilistic ENSO Forecast

Published: October 9, 2014



CPC/IRI Early-Month Consensus ENSO Forecast Probabilities

Season La Niña Neutral El Niño
SON 2014 ~0% 49% 51%
OND 2014 ~0% 38% 62%
NDJ 2014 1% 32% 67%
DJF 2014 1% 34% 65%
JFM 2015 1% 36% 63%
FMA 2015 2% 40% 58%
MAM 2015 3% 45% 52%
AMJ 2015 5% 47% 48%
MJJ 2015 8% 49% 43%

IRI ENSO Forecast

IRI/CPC ENSO Predictions Plume

Published: October 16, 2014

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 (2014-2015)
Model OND NDJ DJF JFM FMA MAM AMJ MJJ JJA
Dynamical models
NCEP CFS version 2 0.5 0.6 0.6 0.6 0.7 0.8 0.9 1.1
NASA GMAO model 0.7 0.8 1 1 1 1 1
Japan Met. Agency model 0.6 0.7 0.7 0.7 0.7
Scripps Inst. HCM 0.9 1 1 1 0.9 0.7 0.6 0.5 0.5
Lamont-Doherty model 0.3 0.3 0.3 0.3 0.3 0.6 1.1 1.5 1.6
POAMA (Austr) model 0.5 0.4 0.4 0.4 0.5 0.5 0.6
ECMWF model 0.7 0.8 0.9 0.8 0.8
UKMO model 0.4 0.2 0.1 0
KMA (Korea) SNU model 0.6 0.7 0.7 0.8 0.8 0.7 0.7 0.6 0.6
ESSIC Intermed. Coupled model 0.5 0.5 0.4 0.3 0.2 0.1 -0.1 -0.3 -0.4
COLA CCSM3 model -0.1 -0.2 -0.1 0 0.1 0.2 0.1 0 -0.1
MÉTÉO FRANCE model 0.7 0.8 0.7 0.7 0.7
CSIR-IRI 3-model MME 0.6 0.8 1.1 1 0.8 0.7
GFDL CM2.1 Coupled Climate model 0.9 1.1 1.3 1.3 1.3 1.2 1.1 1 0.9
Canadian Coupled Fcst Sys 0.8 1 1.1 1.1 1.1 1.1 0.9 0.9 0.8
GFDL CM2.5 FLOR Coupled Climate model 0.7 0.8 0.8 0.9 0.9 0.8 0.7 0.5 0.3
Average, dynamical models 0.6 0.6 0.7 0.7 0.7 0.7 0.7 0.6 0.5
Statistical models
NCEP/CPC Markov model 0.5 0.6 0.7 0.7 0.7 0.6 0.6 0.5 0.5
NOAA/CDC Linear Inverse 0.4 0.3 0.3 0.2 0.2 0.1 0.1 0.1 0.1
NCEP/CPC Constructed Analog 0.8 0.9 0.9 0.9 0.7 0.7 0.5 0.4 0.3
NCEP/CPC Can Cor Anal 1.3 1.3 1.1 0.9 0.7 0.7 0.6 0.5 0.4
Landsea/Knaff CLIPER 0.8 0.8 0.8 0.9 0.9 1 1 0.9 0.7
Univ. BC Neural Network 0.5 0.6 0.6 0.6 0.7 0.7 0.7 0.7 0.7
FSU Regression 0.8 0.9 0.9 0.8 0.7 0.7 0.7 0.7 0.7
TCD – UCLA 0.5 0.5 0.5 0.4 0.3 0.2 0.2 0.2 0.2
UNB/CWC Nonlinear PCA 0.3 0.3 0.2 0.2 0.1 0.1 0.1 0.1 0.2
Average, statistical models 0.6 0.7 0.7 0.6 0.5 0.5 0.5 0.5 0.4
Average, all models 0.6 0.6 0.7 0.7 0.7 0.6 0.6 0.6 0.5

Discussion of Current Forecasts

Most of the set of dynamical and statistical model predictions issued during late September and early October 2014 predict an onset of weak El Niño conditions during northern fall 2014, lasting through winter 2014-15 and well into spring 2015. Development of El Niño conditions appears approximately 60-65% likely for the Oct-Dec and Nov-Jan 2014-15 season, rising to 65-70% for the Dec-Feb 2014-15 through Mar-May 2015. In the most recent week, the SST anomaly in the Nino3.4 region was 0.4 C, reflecting warmish but ENSO-neutral conditions. The monthly anomalous SSTs in the Niño3.4 region were 0.20 and 0.45 C for August and September, respectively. 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
OND 2014 ~0% 35% 65%
NDJ 2014 ~0% 34% 66%
DJF 2014 ~0% 33% 67%
JFM 2015 ~0% 33% 67%
FMA 2015 ~0% 33% 67%
MAM 2015 ~0% 35% 65%
AMJ 2015 ~0% 39% 61%
MJJ 2015 3% 42% 55%
JJA 2015 8% 44% 48%

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.