Monitoring the vast equatorial Pacific requires a global constellation of satellite altimeters, moored ocean buoys, autonomous Argo profiling floats, and standardized geographic index regions.
The Four Standardized Niño Regions
To quantify thermal anomalies across different sections of the 13,000-kilometre equatorial Pacific span, oceanographers divided the ocean into four standardized geographic boxes:
| Niño Region | Geographic Coordinates | Primary Significance |
|---|---|---|
| Niño 1+2 | 0°–10°S, 90°W–80°W | Coastal waters off Peru and Ecuador; measures coastal upwelling and fisheries. |
| Niño 3 | 5°N–5°S, 150°W–90°W | Eastern equatorial Pacific; captures the eastern extension of the cold tongue. |
| Niño 3.4 | 5°N–5°S, 170°W–120°W | Central equatorial Pacific; the primary international benchmark for ENSO operational status. |
| Niño 4 | 5°N–5°S, 160°E–150°W | Western-central Pacific warm pool edge; critical for detecting Central Pacific (Modoki) events. |
Current Weekly Index Values
| Niño Region | Coordinates | SST (°C) | SST Anomaly | Thermal Status |
|---|---|---|---|---|
| Niño 1+2 | 0°–10°S, 90°W–80°W | 26.1 °C | +5.3 °C | Extreme Coastal Warming |
| Niño 3 | 5°N–5°S, 150°W–90°W | 29.0 °C | +4.0 °C | Very Strong |
| Niño 3.4 (Standard) | 5°N–5°S, 170°W–120°W | 29.9 °C | +3.2 °C | Very Strong El Niño |
| Niño 4 | 5°N–5°S, 160°E–150°W | 29.9 °C | +1.2 °C | Moderate Warmth |
Centered on week 30SEP2026. Data: NOAA CPC OISSTv2.1.
The Oceanic Niño Index (ONI) Formula
The Oceanic Niño Index (ONI) is NOAA’s primary metric for tracking ENSO. It calculates a 3-month running mean of ERSST.v5 sea surface temperature anomalies in the Niño 3.4 region. An official El Niño requires anomalies of +0.5 °C or warmer to persist for at least five consecutive overlapping three-month seasons, accompanied by consistent atmospheric wind anomalies.
| Season | Year | Total SST (°C) | Anomaly (°C) | Classification |
|---|---|---|---|---|
| JAS | 2026 | 29.12 | +2.16 | Very Strong El Niño |
| JJA | 2026 | 29.09 | +1.80 | Strong El Niño |
| MJJ | 2026 | 29.02 | +1.39 | Moderate El Niño |
| AMJ | 2026 | 28.74 | +0.95 | Weak El Niño |
| MAM | 2026 | 28.09 | +0.46 | Neutral |
| FMA | 2026 | 27.34 | +0.11 | Neutral |
| JFM | 2026 | 26.57 | -0.21 | Neutral |
| DJF | 2026 | 26.15 | -0.39 | Neutral |
| NDJ | 2025 | 25.96 | -0.60 | La Niña |
| OND | 2025 | 26.04 | -0.61 | La Niña |
Observational Infrastructure: From Satellites to Argo
- TAO/TRITON Moored Array: An array of roughly 70 anchored deep-sea buoys measuring surface winds, humidity, air temperature, and subsurface water temperatures down to 500 metres.
- Argo Profiling Floats: An autonomous global fleet of thousands of robotic floats that descend to 2,000 metres depth every 10 days, measuring salinity and thermal profiles before transmitting data via satellite.
- Satellite Radar Altimeters: Satellites like Sentinel-6 and Jason-3 measure sea surface height; warm water expands, allowing satellites to detect subsurface Kelvin waves through millimetre-scale variations in sea level.