The ocean
surface · subsurface · Niño indicesEl Niño is, above all, warm water spreading east across the equatorial Pacific. Here are the daily anomaly maps, the four Niño indices computed every day, and the heat stored below the surface.
Daily sea surface temperature anomaly
NOAA OISST v2.1 (1° grid) minus the 1991–2020 daily climatology. The last ~14 days come from the preliminary product and are replaced by the final one when it is released. Use the control to animate the 118 available days.
01Daily Niño indices
Anomaly in the four Niño regions
Area-weighted means, every day since 1981. Niño 1+2 (off the coast of Peru) usually jumps first and highest; Niño 3.4 is the reference used to classify the event; Niño 4 shows how far the warming has reached into the west-central Pacific.
Validation: our daily index vs. the CPC weekly index
7-day mean of the Niño 3.4 computed here (Wednesday ±3 days) against the official weekly value. Differences of a few hundredths are expected: CPC uses the 0.25° grid and rounds to one decimal.
Subsurface heat (0–300 m)
Mean temperature anomaly of the upper 300 m of the equatorial Pacific (GODAS). It usually leads the surface by a few months: when it starts to fall, the El Niño peak is near.
02Official monthly indices
ONI, RONI and monthly Niño 3.4
The ONI is the 3-month running mean of the Niño 3.4 anomaly (ERSSTv5) and officially defines an event: 5 consecutive seasons above +0.5 °C. Since 2025 CPC uses the RONI, which subtracts the mean anomaly of the whole tropics — with the entire ocean warmer, only the relative excess drives the atmosphere as El Niño.