Current Information
Summary of ENSO Model Forecasts
17 September 2002
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 eight 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 October than when they are made
between January and April. 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
August and early September shows a range of possible sea surface temperature
conditions for the coming 3 to 8 months (October-November-December 2002
through May-June-July 2003). Most models are indicating a continuation
of warm conditions. 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 November-December-January 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 November-December-January
period comes from the Lamont-Doherty (LDEO) simple coupled model from Columbia
University, U.S. (1.65 degrees C above normal), and the coldest one is
from the NOAA CDC's statistical Linear Inverse Model, calling for SST anomalies
0.1 to 0.2 degrees C below normal. The SST anomalies forecast by the models
for November-December-January tend to be forecast also for slightly later
periods, such as January-February-March 2003, but a decline toward normal
begins to set in around that time. For this later time, 12 of the 14 models
that forecast to that long a lead time still suggest El Nino conditions:
the NASA/NSIPP, the NCEP, JMA, Scripps, LDEO, BMRC, CSIRO, Korea SNU, CPC
Markov, CPC-CCA, Colorado State CLIPER, and the UBC nonlinear CCA. The
CPC Constructed Analogue and CDC Linear Inverse models predict SSTs that
fall short of El Nino levels for January-February-March, although the Constructed
Analogue indicates El Nino SST levels for the earlier November-December-January
period.
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