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IRI ENSO Forecast

2014 September Quick Look

Published: September 4, 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 July through August the observed ENSO conditions were neutral. Most of the ENSO prediction models indicate warming to El Niño levels coming around early northern fall, peaking at weak strength during winter 2014-15 and lasting into the first few months of 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: September 4, 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: The chance of El Niño is at 60-65% during the Northern Hemisphere fall and winter.

During August 2014, above-average sea surface temperatures (SST) continued across much of the equatorial Pacific (Figure 1). Most of the Niño indices warmed during the month with values of +0.5°C in Niño-4, +0.4°C in Niño-3.4, +0.4°C in Niño-3, and +0.8°C in Niño-1+2 (Figure 2). Subsurface heat content anomalies (averaged between 180º-100ºW) also increased during the month (Figure 3) as above-average subsurface temperatures developed across the central and east-central equatorial Pacific (Figure 4). This warming is associated with the downwelling phase of an equatorial oceanic Kelvin wave triggered in July by low-level westerly wind anomalies. Westerly wind anomalies continued in the central and eastern part of the basin early in August, but weakened by the end of the month. Enhanced easterly upper-level wind anomalies have prevailed during much of the month, and the Southern Oscillation Index has been negative. However, convective cloudiness remained generally near average over most of the region, except for below average cloudiness observed across the central and western Pacific (Figure 5). The lack of a coherent atmospheric El Niño pattern and near-average SSTs in the central Pacific indicate a continuation of ENSO-neutral.

Most of the models continue to predict El Niño to develop during September-November and to continue into early 2015 (Figure 6). A majority of models and the multi-model averages favor a weak El Niño. At this time, the consensus of forecasters expects El Niño to emerge during September-October and to peak at weak strength during the late fall and early winter (3-month values of the Niño-3.4 index between 0.5°C and 0.9°C). The chance of El Niño is at 60-65% during the Northern Hemisphere fall and winter (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 9 October 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
ASO 2014 ~0% 57% 43%
SON 2014 ~0% 45% 55%
OND 2014 1% 38% 61%
NDJ 2014 1% 34% 65%
DJF 2014 2% 34% 64%
JFM 2015 3% 36% 61%
FMA 2015 3% 41% 56%
MAM 2015 4% 48% 48%
AMJ 2015 5% 53% 42%

IRI ENSO Forecast

IRI Technical ENSO Update

Published: August 21, 2014

Recent and Current Conditions

The SST anomaly in the Nino3.4 region in recent weeks retreated from near the borderline of neutral and El Niño where it had been in May and June. For July the Nino3.4 SST anomaly was 0.18 C, indicative of neutral conditions, and for May-July it was 0.37 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 0.0 C, not far from the 0.18 C observed in July. 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. During August so far, neither ocean nor atmosphere has reflected El Niño conditions in a clear or obvious way, but the atmosphere is recently showing a renewed tendency toward El Niño development.

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 early fall 2014 about to begin, with probabilities of El Niño rising to 66% for Nov-Jan 2014-15. The latest set of model ENSO predictions, from mid-August, now available in the IRI/CPC ENSO prediction plume, is discussed below. Currently, Nino3.4 SST anomalies are neutral after having been close to the borderline of El during May and June. Positive anomalies are still found in the far eastern part of the Pacific basin. Subsurface temperature anomalies across the eastern equatorial Pacific have been at average levels during the last month, after being much above average during spring but subsequently decreasing due to discharging into the atmosphere with strong positive SST anomalies in the far eastern part of the basin.  In the atmosphere, the basin-wide sea level pressure pattern (e.g. the SOI) has recently shown a tendencies in the direction of El Niño, with a negative SOI, weak anomalous low-level westerlies and anomalous upper level easterlies.  Anomalous convection (as measured by OLR) has been near average near and east of the dateline.  These atmospheric conditions, while weak, are suggestive of El Niño despite the SST being neutral in recent weeks. Together, the oceanic and atmospheric features continue to reflect neutral ENSO conditions that lean toward weak El Niño.

As of mid-August, none of the dynamical or statistical models models predicts La Niña SST conditions for the initial Aug-Oct 2014 season, 44% predicts El Niño conditions, and 56% 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 Nov-Jan 2014-15 season, among models that do use subsurface temperature information, 40% predicts ENSO-neutral SSTs, 60% predicts El Niño conditions and none predicts La Niña conditions. For all model types, the probability for neutral ENSO conditions is 40% or below between Oct-Dec 2014 and Apr-Jun 2015. Probabilities for El Niño rise to more than 60% or more between these same two seasons, peaking at 71% for Dec-Feb 2014-15. No model predicts La Niña conditions for any of the 3-month periods between Aug-Oct 2014 and Apr-Jun 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 Aug-Oct 2014 through Jan-Mar 2015, rising to 4% by Apr-Jun.  Model probabilities for neutral ENSO conditions are 58% for the initial period of Aug-Oct 2014, 44% for the next running period of Sep-Nov, reach a low of 27% for Dec-Feb 2014-15 and rise to 45% by Apr-Jun 2015. Probabilities for El Niño are 42% for Aug-Oct 2014, rise to 73% for Dec-Feb 2014-15, and decline dlowly to 51% for Apr-Jun 2015. The models collectively favor El Niño over other ENSO conditions by a clear margin between Oct-Dec 2014 and Feb-Apr 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 Sep-Nov 2014, becoming even more likely by Oct-Dec. The consensus of model predictions calls for a weak El Niño event, a moderate event being second most likely, no El Nino being next most likely, and a strong event being least likely. 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: August 21, 2014



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

Season La Niña Neutral El Niño
ASO 2014 ~0% 58% 42%
SON 2014 ~0% 44% 56%
OND 2014 ~0% 36% 64%
NDJ 2014 ~0% 30% 70%
DJF 2014 ~0% 27% 73%
JFM 2015 ~0% 32% 68%
FMA 2015 1% 37% 62%
MAM 2015 2% 43% 55%
AMJ 2015 4% 45% 51%

IRI ENSO Forecast

CPC/IRI Consensus Probabilistic ENSO Forecast

Published: September 4, 2014



CPC/IRI Early-Month Consensus ENSO Forecast Probabilities

Season La Niña Neutral El Niño
ASO 2014 ~0% 57% 43%
SON 2014 ~0% 45% 55%
OND 2014 1% 38% 61%
NDJ 2014 1% 34% 65%
DJF 2014 2% 34% 64%
JFM 2015 3% 36% 61%
FMA 2015 3% 41% 56%
MAM 2015 4% 48% 48%
AMJ 2015 5% 53% 42%

IRI ENSO Forecast

IRI/CPC ENSO Predictions Plume

Published: August 21, 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 ASO SON OND NDJ DJF JFM FMA MAM AMJ
Dynamical models
NCEP CFS version 2 0.5 0.9 1.1 1.1 1 0.9 0.9 0.8
NASA GMAO model 0.5 0.7 0.8 0.8 0.8 0.8 0.8
Japan Met. Agency model 0.2 0.4 0.5 0.7 0.7
Scripps Inst. HCM 1.1 1.2 1.2 1.3 1.2 1 0.8 0.6 0.4
Lamont-Doherty model 0.4 0.3 0.2 0.2 0.2 0.3 0.3 0.3 0.6
POAMA (Austr) model 0.1 0.2 0.3 0.3 0.4 0.4 0.4
ECMWF model 0.6 0.9 1.1 1.2 1.2
UKMO model 0.4 0.4 0.4 0.3
KMA (Korea) SNU model 0.7 0.9 0.9 1 1 1 0.9 0.9 0.8
ESSIC Intermed. Coupled model 0.2 0.2 0.3 0.3 0.3 0.2 0.1 0 -0.1
COLA CCSM3 model 0.8 1 1.2 1.4 1.6 1.6 1.4 1.1 0.7
Japan Frontier Coupled model 0.7 0.8 0.8 0.8 0.9 0.9 0.9 0.8 0.8
CSIR-IRI 3-model MME 0.6 0.7 0.9 1.1 1.3 1.1
GFDL CM2.1 Coupled Climate model -0.1 0 0 0.1 0.2 0.3 0.5 0.6 0.7
Canadian Coupled Fcst Sys 0.6 0.8 1 1.1 1.1 1.1 1.1 1 0.8
GFDL CM2.5 FLOR Coupled Climate model 0.2 0.3 0.4 0.4 0.5 0.7 0.8 0.8 0.8
Average, dynamical models 0.5 0.6 0.7 0.7 0.8 0.8 0.7 0.7 0.6
Statistical models
NCEP/CPC Markov model 0.2 0.3 0.4 0.6 0.6 0.6 0.6 0.5 0.5
NOAA/CDC Linear Inverse 0.2 0.2 0.1 0.1 0 0 -0.1 -0.1 -0.1
NCEP/CPC Constructed Analog 0.6 0.8 1 1.2 1.2 1.1 0.8 0.7 0.5
NCEP/CPC Can Cor Anal 0.5 0.5 0.6 0.6 0.5 0.5 0.4 0.4 0.4
Landsea/Knaff CLIPER 0.6 0.9 1.2 1.5 1.3 1.1 0.9 0.8 0.7
Univ. BC Neural Network 0.6 0.8 0.8 0.8 0.9 0.8 0.8 0.7 0.6
FSU Regression 0.1 0.2 0.2 0.3 0.3 0.3 0.3 0.4 0.5
TCD – UCLA 0.4 0.6 0.7 0.8 0.8 0.8 0.8 0.7 0.7
UNB/CWC Nonlinear PCA 0.2 0.2 0.1 0 0 0 0 0 0.1
Average, statistical models 0.4 0.5 0.6 0.7 0.6 0.6 0.5 0.5 0.4
Average, all models 0.4 0.6 0.6 0.7 0.7 0.7 0.6 0.6 0.5

Discussion of Current Forecasts

Most of the set of dynamical and statistical model predictions issued during late July and early August 2014 predict a transition from neutral ENSO conditions to weak El Nino conditions during northern early fall 2014 with some further warming predicted into late fall and winter 2014-15. Development of El Nino conditions appears approximately 50% likely for the Aug-Oct or Sep-Nov seasons of 2014, and rises to 70-75% by Nov-Jan and Dec-Feb 2014-15. In the most recent week, the SST anomaly in the Nino3.4 region was 0.0 C, reflecting neutral conditions. The monthly anomalous SSTs in the Nino3.4 region were near 0.5 during May and June, but returned to neutral levels during July and August. 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 2014 ~0% 58% 42%
SON 2014 ~0% 44% 56%
OND 2014 ~0% 36% 64%
NDJ 2014 ~0% 30% 70%
DJF 2014 ~0% 27% 73%
JFM 2015 ~0% 32% 68%
FMA 2015 1% 37% 62%
MAM 2015 2% 43% 55%
AMJ 2015 4% 45% 51%

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.