El Nino Watch

IRI ENSO forecast (plume and probabilities)

Columbia University's monthly summary of about 20 computer models: for each 3-month season ahead, the chance of El Nino, neutral or La Nina.

Forecasts and bulletins

The International Research Institute for Climate and Society (IRI) collects forecasts of the Nino 3.4 anomaly from many models (22 in the current release: 13 dynamical and 9 statistical).

  • The plume is a chart with one line per model for the next 9 overlapping 3-month seasons. When the lines are close together, the models agree.
  • The probabilities turn this into chances for each season: El Nino (+0.5 °C or more), neutral (-0.5 to +0.5 °C), La Nina (-0.5 °C or less). The three add up to 100%.

Seasons are named by their months' initials: SON = September-October-November, DJF = December-January-February, and so on (see Season codes (DJF, JJA, SON...)).

How to read it

Read the bar for each season: the red part is the El Nino chance. 90% means "9 chances in 10"; it is not a measure of strength. A forecast for 8 months ahead is much less reliable than one for next season (see Forecast uncertainty and the spring barrier).

Why it matters for Koh Samui

It tells you how long El Nino conditions are likely to last. If El Nino is still likely through February-April 2027, Samui's dry season is likely to be affected.

Example

IRI September 2026: El Nino probability 100% from SON 2026 through FMA 2027, 99% in MAM 2027, 90% in AMJ 2027, then 61% in MJJ 2027.

Sources

Related

ENSO status now

ONI (NOAA CPC)
+1.80 °C, JJA 2026 (previous +1.39 °C)
RONI (NOAA CPC)
+1.36 °C, JJA 2026
Nino 3.4 weekly (NOAA CPC / OISST)
+3.0 °C anomaly, week of 16 Sep 2026 (SST 29.6 °C)