Current ENSO Information

Summary of Model Forecasts

Summary of ENSO Model Forecasts

16 December 2002

>	Note on interpreting model forecasts
>	Discussion of current forecasts
>	Figure of Nino3.4 SST forecasts
>	Table of Nino3.4 SST forecasts
>	Notes on the data

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 November than when they are made between January 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.

Discussion of current forecasts

The set of dynamical and statistical model forecasts issued during late September and early October shows a range of possible sea surface temperature conditions for the coming 2 to 9 months (December-January-February 2002-03 through August-September-October 2003). Nearly all models are indicating a continuation of warm conditions, followed by a slow weakening of the warmth during the first half of 2003. Most of the models forecast warming sufficient to be called an El Nino (e.g., warming to 0.6 degrees C or more above average in the Nino 3.4 region for the January-February-March seasonal average). A small number are forecasting ENSO conditions in the neutral category--less than 0.6 degrees C away from normal. The warmest forecast for the January-February-March period comes from the NASA/NSIPP model [2.11 degrees C above normal), and the coldest one is from the Colorado State Univ CLIPER calling for SST anomalies of -0.02 degrees C. For March-April-May 2003, 12 of the 16 models still suggest El Nino conditions (0.5 degrees or more for that season): all except for the Australian POAMA, the ECMWF, the NOAA/CDC Linear Inverse, and the Colorado State Univ. CLIPER.

SST forecasts

Table 1. Forecast SST Anomalies (deg C) in the Nino 3.4 Region

	Season (2002-2003)
Model	DJF	JFM	FMA	MAM	FMA	MJJ	JJA	JAS	ASO
*Dynamical models*
NASA/NSIPP model	2.1	2.0	1.9	1.8	1.8	1.7	1.6	1.4	1.1
NCEP Coupled model	1.3	0.9	0.7	0.6	0.7	0.9	1.1	1.2
Japanese Met. Agcy. model	1.3	1.2	1.2	1.2	1.3	1.4
Scripps Inst. model	1.1	1.0	0.8	0.7	0.6	0.4	0.3	0.4	0.4
Lamont-Doherty model	1.6	1.5	1.0	0.9	0.7	0.5	0.4
BMRC intermed. model	1.4	1.4	1.4	1.3	1.3	1.3	1.3	1.2
CSIRO model	1.2	1.2	1.2	1.1	1.1	1.1	1.1	1.2
POAMA model	1.1	0.8	0.6	0.2	-0.3	-0.7	-1.0
ECMWF model	1.2	0.8	0.6	0.4
KMA SNU (Korea) model	1.4	1.3	1.2	1.1	0.9	0.8	0.6	0.5	0.3
Average, dynamical models	1.3	1.2	1.0	0.9	0.8	0.7	0.6	0.8
*Statistical models*
NCEP/CPC Markov model	1.5	1.4	1.2	1.2	1.1	1.1	1.0	1.0	1.0
NOAA/CDC Linear Inverse	0.4	0.3	0.1	0.0	0.0	-0.1	-0.1	-0.1	-0.2
Dool Constructed Analog	1.2	1.0	0.8	0.6	0.3	0.0	-0.3	-0.4	-0.5
NCEP/CPC Can Cor Anal	1.2	1.2	1.1	0.9	0.8	0.7	0.6	0.6	0.5
Landsea/Knaff CLIPER	0.1	0.0	-0.1	-0.2	-0.3	-0.4	-0.6	-0.7	-0.8
Univ. BC nonlinear Can Cor	1.0	1.0	1.0	1.0	0.9	0.9	0.9	0.7	0.6
Average, statistical models	0.9	0.8	0.7	0.6	0.5	0.4	0.3	0.2	0.1
Average, all models	1.1	1.0	0.9	0.7	0.7	0.6	0.4	0.5	0.3

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
Regional SST anomaly adjustment using the climatological variances of one region versus that of another

As an example of the last case, suppose only the Nino 3 anomaly is provided. The Nino 3.4 anomaly is then obtained by decreasing the Nino 3 anomaly by the factor defined by the ratio of the year-to-year variance of Nino 3.4 to the year-to-year variance of Nino 3 SST, for the 3-month season in question.

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.

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