2026 El Niño Watch: What Subsurface Data Tells Us — And What 1997 and 2023 Taught Us
Published: May 22, 2026 · 12 min read
On May 14, 2026, NOAA upgraded its ENSO alert from "Final La Niña Advisory" to El Niño Watch. The Niño 3.4 index sits at +0.4°C — just 0.1°C below the official El Niño threshold. But the real story is 150 meters below the surface, where ocean heat content has reached levels that climate scientists describe with words like "immense" and "unprecedented for this time of year."
This article cross-references NOAA's latest ENSO diagnostic discussion, WMO's May-July 2026 seasonal update, subsurface temperature data from the Climate Prediction Center, and historical comparisons to answer one question: what does the data actually tell us about the developing 2026 El Niño?
The Numbers: Where We Stand in May 2026
Let's start with the raw data from NOAA's mid-May 2026 ENSO Diagnostic Discussion:
| Indicator | Value | Status |
|---|---|---|
| Niño 3.4 SST Anomaly | +0.4°C | 0.1°C below El Niño threshold |
| Niño 4 Index | +0.5°C | At El Niño threshold |
| Niño 1+2 Index (eastern edge) | +1.0°C | Already in moderate El Niño territory |
| Subsurface Temperature Anomaly (300m) | +1.6°C | Second-warmest on record for April |
| Temperature at 150m Depth | Up to +5°C | Rivaling 1997 readings |
| ENSO Alert System | — | El Niño Watch |
Two things jump out. First, the east is already warming hard — Niño 1+2 at +1.0°C means the coastal waters off Peru are already feeling it. Second, the subsurface heat is extraordinary. The Climate Impact Company's May 11 analysis ranked upper ocean heat content as "second only to the 1997 El Niño" for this time of year.
Subsurface: Why 150 Meters Down Matters More Than the Surface
Surface temperatures in the Niño 3.4 region are a lagging indicator. The real action is in the subsurface — specifically, the downwelling Kelvin waves traveling eastward along the thermocline at 100–250 meters depth.
In 2026, four significant Kelvin wave events have been detected since December 2025: one in December, another in January, a third in March, and a new one forming in April. Each wave pushes warm water eastward. The Climate Cosmos analysis (May 8, 2026) notes that these waves deliver temperatures "up to 5°C above normal at 150m depth" — a number that "could surpass those preceding the 1997-98 event."
Michelle L'Heureux, head of NOAA's ENSO team, told the Wall Street Journal: "The current Kelvin wave is impressive and, by some measures we look at, it is rivaling the one we saw in 1997."
A useful comparison table:
| Metric (Early Buildup Phase) | 1997-98 | 2026 |
|---|---|---|
| 300m Heat Anomaly (180°–100°W) | ~+1.5°C | +1.6°C |
| Kelvin Wave Activity | Strong series | Strong series (4 detected) |
| Upper-Ocean Heat Trajectory | Rapid rise | Tracking 1997 and 2015 paths |
| Subsurface Temp Monthly Trend | 6+ months warming | 6 consecutive months warming |
But there's an important catch: similar precursors don't guarantee similar outcomes. The spring predictability barrier — a well-documented phenomenon where ENSO forecasts made between March and May have the lowest skill — adds substantial uncertainty. Models can and do shift.
The Forecast Spread: 82% Yes, But How Strong?
NOAA's May 2026 ensemble gives these probabilities:
- El Niño onset by May–July 2026: 82%
- El Niño persisting through Dec 2026–Feb 2027: 96%
- "Very strong" event (Niño 3.4 ≥ +2.0°C) by Nov–Jan: 37%
Those numbers hide a significant model disagreement. The ECMWF model (European Centre) projects a 100% probability of a super El Niño forming by November, with central Pacific temperatures exceeding +3°C. NOAA's own models are more conservative, giving a roughly 1-in-3 chance. Spain's La Vanguardia reported on May 20 that "models give super El Niño only a 25–37% probability, cautioning about the spring predictability barrier."
James Hansen's research group — which has been tracking 300m temperature anomalies — notes that the January–April 2026 trajectory "closely tracks those of 1997 and 2015," two years that preceded super El Niños. But Hansen himself has cautioned that the spring barrier makes peak-strength predictions unreliable until at least July.
What we can say with confidence: El Niño will almost certainly develop. Whether it reaches "super" status is an open question, but the subsurface energy available to fuel it is enormous.
What 2023–24 Taught Us That Changes How We Read 2026
The 2023–24 El Niño — the most recent event and the fifth-strongest on record — provides a fresh calibration for what these numbers translate to on the ground. Here's what that event cost, drawn from WMO summaries and post-event analysis:
- Economic damage: approximately $75 billion globally (WMO estimate)
- People affected: over 60 million across all continents
- Food price impact: global rice prices rose ~30% year-on-year by March 2024 after India banned non-basmati exports
- Southern Africa drought: 30 million people affected across 9 countries; Zambia, Malawi, Zimbabwe declared states of disaster
- Brazil floods (Rio Grande do Sul, May 2024): 850,000 people affected, 78 deaths, intensified by El Niño-modified weather patterns
- Temperature records: 2023 became the hottest year on record; March 2024 hit 1.68°C above pre-industrial levels
A Dartmouth College study published in Science (2023) found something that rewrites how we think about El Niño economics: the damage doesn't stop when the event ends. The 1997-98 event depressed global GDP by $5.7 trillion over the five years following the event. The 1982-83 event cost $4.1 trillion. These persistent effects come from agricultural disruption cascading through supply chains, infrastructure damage that takes years to repair, and the compounding effect of reduced investment during recovery periods.
Here's the key lesson for 2026: the 2023-24 event happened on top of already-elevated global temperatures from climate change. The baseline ocean is warmer now than in 1997. If a 1997-magnitude event unfolds on top of 2026's warmer baseline, the absolute sea surface temperatures — and the atmospheric response — could be more extreme than anything in the historical record.
Regional Outlook: Where the Pain Points Are
Based on the composite of 1997, 2015, and 2023 event patterns, here's what tends to happen — with the caveat that every El Niño is different:
High Confidence: Drier and Hotter
- Southern Africa: drought risk elevated. After the 2023-24 event's devastation, even a moderate El Niño would compound food insecurity that hasn't fully recovered.
- Southeast Asia and India: weakened monsoon. India's 2023 August rainfall was the driest since 1901 during the last event. Rice-exporting nations (India, Thailand, Vietnam, Indonesia) face crop pressure.
- Northern Brazil and the Amazon: drought conditions. Even without El Niño, the Amazon has been experiencing record-low river levels.
- Australia: elevated bushfire risk, especially Queensland and NSW. Reduced winter-spring rainfall in the east.
High Confidence: Wetter and Flood-Prone
- Peru and Ecuador: coastal flooding. The 1997-98 event caused over 200 deaths in Peru from flooding and landslides.
- Southern Brazil, Uruguay, northern Argentina: increased rainfall, flood risk.
- California and southern US: wetter winter, potential for atmospheric river events. The 2023-24 event brought Tropical Storm Hilary ($900M damage) to Southern California.
- East Africa: heavy rains, flooding, disease outbreak risk (cholera, malaria patterns shift with rainfall).
The Wild Card: Eastern Pacific Hurricanes
The 2023-24 event saw Hurricane Otis intensify from a tropical storm to a Category 5 in 12 hours before hitting Acapulco — a rate of intensification that forecast models completely failed to predict. Warm eastern Pacific waters from El Niño create conditions where rapid intensification becomes more likely. Mexico's Pacific coast and Baja California face elevated risk.
Why This Event Could Be Different — In a Bad Way
Three factors make the 2026 El Niño worth watching more carefully than a typical event:
1. The baseline is higher. Global mean temperatures are roughly 0.3°C warmer than in 1997-98. An El Niño of the same magnitude as 1997 would push absolute temperatures into territory never recorded. The 2023 event — only the fifth-strongest — was enough to make 2023 the hottest year on record. A stronger event on a warmer baseline has no precedent.
2. The subsurface energy is there. Six consecutive months of increasing subsurface heat content is an unusual signal. The Climate Impact Company notes that "upper ocean heat east of the dateline is the second-warmest historically, with trajectories tracking 1997 and 2015." The fuel is loaded.
3. Compounding crises. Southern Africa hasn't recovered from 2023-24. Global rice stocks are still tight. The Amazon is already stressed. Insurance markets in flood-prone and fire-prone regions are fragile (several major insurers have pulled out of California and Florida). An El Niño doesn't happen in isolation — it lands on top of existing vulnerabilities.
The Spring Predictability Barrier: What We Can't Know Yet
It's important to be honest about uncertainty. The "spring predictability barrier" isn't a theoretical concern — it's a statistical reality of ENSO forecasting. Between March and May, the signal-to-noise ratio in climate models degrades. Dr. L'Heureux's team at NOAA explicitly notes that while "confidence in El Niño onset is high, there remains substantial uncertainty in peak strength."
The models will become more reliable by July–August. Key things to watch:
- Sustained westerly wind anomalies in the western Pacific — without these, Kelvin waves lose their punch
- Atmosphere-ocean coupling: is the atmosphere responding to the ocean warming, or is the ocean warming on its own?
- Niño 3.4 crossing +0.5°C and staying there for at least 3 consecutive overlapping 3-month periods (the official El Niño declaration threshold)
- SOI (Southern Oscillation Index) turning persistently negative
If you want to track this yourself: NOAA's CPC releases weekly ENSO updates every Monday. The Climate Prediction Center's ENSO Diagnostic Discussion comes out on the second Thursday of each month. Those are the primary sources — everything else is interpretation.
Bottom Line
The data says: El Niño is coming. The questions are how strong, how long, and how much damage. The subsurface heat signal is the strongest since 1997. The forecast models agree on onset but disagree on peak intensity. And the world this El Niño lands on is warmer, more fragile, and still recovering from the last one.
The 2023-24 event taught us that even a "moderate-strong" El Niño (peaking at +2.0°C) can cause $75 billion in damage and affect 60 million people — when it happens on top of climate change-warmed oceans. If 2026 produces a 1997-magnitude event, we are in uncharted territory.
Data sources: NOAA Climate Prediction Center ENSO Diagnostic Discussion (May 14, 2026); WMO Global Seasonal Climate Update (April 2026); Climate Impact Company weekly ENSO diagnostics (May 11, 2026); Climate Cosmos subsurface analysis (May 8, 2026); Dartmouth College "Persistent effect of El Niño on global economic growth" (Science, 2023); WMO 2023-2024 El Niño event summary; The Weather Network ENSO forecast analysis (March 2026); La Vanguardia model ensemble analysis (May 20, 2026).