Anomaly

Indices

Almost every climate number in this app is an anomaly, not a raw value.

Why: the ocean near the equator is always warm, and the dry season is always dry. What matters is whether it is warmer, wetter or drier than usual for that time of year. So scientists subtract the normal value (the climatology) from the measured value.

• A positive anomaly (+) = above normal.
• A negative anomaly (-) = below normal.
• Zero = exactly normal.

Example

The Nino 3.4 region is normally about 27 to 28 °C at this time of year. If the measured 3-month mean is 29.09 °C and the normal for those months is 27.29 °C, the anomaly is +1.80 °C.

Sources

• NOAA CPC -- Oceanic Nino Index table (ERSSTv6)
• NCAR Climate Data Guide -- Nino SST indices

Related

• Climatology and the 1991-2020 baseline
• SST anomaly
• ONI (Oceanic Nino Index)
• Rain as % of normal

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)