IRI ENSO Forecast


Published: September 10, 2020

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: La Niña Advisory

SynopsisLa Niña conditions are present and are likely to continue through the Northern Hemisphere winter (~75% chance). 

In August, La Niña conditions were present, with below-average sea surface temperatures (SSTs) extending across the central and eastern equatorial Pacific Ocean (Fig. 1). In the last week, all Niño indices were negative, with the Niño-3.4 index at -0.9ºC and the Niño-1+2 and Niño-3 indices cooler than -1.0ºC (Fig. 2). Equatorial subsurface temperature anomalies averaged across 180°-100°W were negative (Fig. 3), with the largest departures observed in the east-central Pacific from the surface to 200m depth (Fig. 4). Atmospheric circulation anomalies over the tropical Pacific were also generally consistent with La Niña, despite sub-seasonal variability during the month.  The low-level and upper-level winds were near average for the month as a whole, but enhanced low-level easterly winds were prominent across the equatorial Pacific Ocean during early and late August.  Tropical convection remained suppressed over the western and central Pacific, and was near average over Indonesia (Fig. 5). Both the Southern Oscillation and Equatorial Southern Oscillation indices were positive.  Overall, the coupled ocean-atmosphere system was consistent with La Niña conditions.

A majority of the models in the IRI/CPC plume predict the continuation of La Niña (Niño-3.4 index less than -0.5°C) through the Northern Hemisphere winter 2020-21 (Fig. 6). The forecaster consensus supports that view, and favors a borderline moderate event (Niño-3.4 index near -1.0ºC) during the peak November-January season.  In summary, La Niña conditions are present and are likely to continue through the Northern Hemisphere winter (~75% chance; click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

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 8 October 2020. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to:

CPC/IRI Early-Month Official ENSO Forecast Probabilities

Season La Niña Neutral El Niño
ASO 2020 73% 27% 0%
SON 2020 77% 22% 1%
OND 2020 79% 20% 1%
NDJ 2020 78% 20% 2%
DJF 2020 74% 23% 3%
JFM 2020 65% 29% 6%
FMA 2020 52% 40% 8%
MAM 2020 38% 50% 12%
AMJ 2020 29% 53% 18%

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