El Niño / La Niña - ENSO Tracker
The El Niño–Southern Oscillation (ENSO) is the single biggest year-to-year driver of global temperature and rainfall after the long-term warming trend itself. It is also a natural amplifier of climate change. During an El Niño, unusually warm water piles up in the eastern tropical Pacific, releasing heat to the atmosphere and lifting global mean temperature by ~0.1–0.3°C for 6–12 months. La Niña does the opposite. ENSO also shifts rainfall and storm tracks worldwide - driving drought in Australia, flooding in Peru, wetter Californias and milder UK winters. Record-warm years almost always coincide with El Niño stacked on top of the long-term warming trend.
ONI stands for Oceanic Niño Index; RONI stands for Relative Oceanic Niño Index, and both measure Sea Surface Temperature (SST) for the Niño 3.4 region - RONI (NOAA’s official index since Feb 2026) subtracts the tropics-wide warming background so strength is judged consistently across the decades.
Current State - El Niño
Niño 3.4 (central Pacific) is the official ENSO yardstick. Niño 1+2 leads coastal signals off Peru; Niño 4 captures the western warm pool.
ENSO state
intensifying93% very strong at peak · Sep-NovWarm Pacific - Global Temperatures Rise
RONI · 3-mo3-month mean
El Niño
+1.4°C · JJA 2026 · ONI +1.8°C
Niño 3.4 · latest
SST 29.4°C · w/e 26-08-26
Equatorial Pacific
The red/blue glow shows the latest week’s SST anomaly vs the 1991-2020 baseline. Orange marks the Indo-Pacific Warm Pool, spreading east under El Niño. Arrows show trade-wind direction.
Niño 1+2
Very strong El Niño-leaning
SST 25.0°C
Niño 3
Very strong El Niño-leaning
SST 28.3°C
Niño 3.4
Very strong El Niño-leaning
SST 29.4°C
Niño 4
Moderate El Niño-leaning
SST 29.6°C
El Niño years push global temperatures higher; La Niña years temporarily damp them - though the underlying greenhouse-gas trend continues either way. Thresholds: ≥ +0.5°C El Niño · ≤ −0.5°C La Niña · otherwise Neutral.
ENSO Forecast
El Niño - Niño 3.4 Observed & Forecast (RONI)
Solid = observed, dashed = forecast. Teal = raw weekly SST, ~2 months ahead of RONI's latest reading (shaded gold).
What's Coming
NOAA forecast
Very Strong at peakPeak +2.7/+3.1°C (RONI/ONI median)
El Niño conditions are already in place and forecast to peak at 100% probability in JAS-JFM. The dashed off-white curve is NOAA’s own official RONI outlook, peaking in OND 2026. The current forecast was issued August 2026.
SNU AI forecast
Very Strong at peakPeak +2.3/+2.8°C (RONI/ONI)
The dashed purple curve is a deep-learning forecast from Seoul National University, built for predictions up to 18–24 months out. The current forecast was issued August 2026.
Season-by-Season El Niño Probability · Shaded by Strength
Three ENSO indicators on one axis: Niño 3.4 (ocean), MEI v2 (ocean+atmosphere) and −SOI (sign-flipped so all three rise together for El Niño). When all three climb past +0.5, the forecast has independent support.
Indicators: NOAA CPC Niño-region SSTs, NOAA PSL MEI v2, NOAA CPC SOI.
Sources: NOAA CPC weekly Niño 3.4 SST (observed), NOAA official RONI outlook and NOAA CPC probability outlook (forecast), NOAA RONI (legacy ONI v5 kept for continuity), and NOAA CPC strength outlook, and SNU ACE Lab CNN forecast (Ham et al. 2019, Nature). RONI methodology: Stockdale (2026, ECMWF). Raw model forecasts are converted to RONI using the observed seasonal ONI−RONI gap (currently ~+0.4–0.5°C).
Strongest ENSO Events on Record
Top 6 episodes since 1950 by peak RONI (NOAA’s warming-adjusted index).
El Niño
La Niña
Bars = peak RONI per episode; (raw x) = un-adjusted Niño 3.4 SST.
Global Impact Tracker
ENSO's Global Footprint
Scrub the timeline of ENSO years below, each labelled by its event (1997-98, 2015-16). Colours show how each country's temperature or precipitation departed from its 1961-1990 baseline during that event's winter peak or the spring after it. The four boxes over the equatorial Pacific mark the Niño SST regions.
Loading impact map…
Past Major Events (1954-2026)
What Happened Last Time?
The fifteen most consequential ENSO events since 1950. Bar height shows peak RONI (NOAA's official warming-adjusted index).
2023-2024 El Niño
strong +1.5/+2.0°C (RONI/ONI)Peaked DJF 2023-24. Combined with the long-term warming trend, helped make 2023 and then 2024 the two hottest years on record by clear margins.
- 2024: first calendar year >1.5 °C above pre-industrial (Copernicus)
- Record Amazon drought (lowest Rio Negro at Manaus)
- Mediterranean & North Atlantic marine heatwaves
- Global mass coral bleaching #4 (declared April 2024)
Most reliable footprint: Suriname ran +1.5°C that winter - ENSO alone explains ~55% of its year-to-year swing; Venezuela and Bolivia moved almost as tightly with it.
2020-2023 La Niña
strong -1.5/-1.3°C (RONI/ONI)A rare triple-dip La Niña (3 successive winters). Cumulative impacts much larger than any single winter would suggest.
- Horn of Africa drought - worst in 40 years (~20M food-insecure)
- Hyperactive 2020 Atlantic hurricane season (30 named storms)
- 2022 Pakistan floods (~33M affected, ~8M displaced)
- Reinforced US SW megadrought
Most reliable footprint: Botswana ran -1.6°C in the first of its three winters - ENSO alone explains ~44% of its year-to-year swing, holding up consistently across this rare triple-dip event.
2014-2016 El Niño
very strong +2.4/+2.8°C (RONI/ONI)A "Godzilla" El Niño - peak RONI on par with 1997-98. Pushed global temperature ~0.2 °C above the long-term trend at peak.
- 2015 & 2016 set successive global temperature records
- Ethiopia & Southern Africa drought (~60M people food-insecure)
- Indonesia fires (worst since 1997)
- Global mass coral bleaching #3 (2014-17)
Most reliable footprint: Botswana ran +0.9°C that winter - ENSO alone explains ~44% of its year-to-year swing. This "Godzilla" event’s headline record warmth was global and trend-driven; the reliably ENSO-attributable part of its footprint was smaller and concentrated in the tropics/southern Africa.
2010-2011 La Niña
strong -1.7/-1.6°C (RONI/ONI)Co-incident with the strongest negative Southern Oscillation Index since 1917. Drove some of the most extreme rainfall events on record.
- QLD & Brisbane floods (Jan 2011)
- Pakistan floods (mid-2010, 20M affected)
- 2010 Russian heatwave (linked indirectly)
- Horn of Africa drought (2010-12)
Most reliable footprint: Namibia ran -1.1°C that winter - ENSO alone explains ~48% of its year-to-year swing. The 2010 Russian heatwave above is the opposite kind of story: real, but driven mostly by blocking, not ENSO - Russia’s own ENSO link tests at close to zero in this dataset.
2007-2008 La Niña
strong -1.6/-1.6°C (RONI/ONI)A strong, fast-developing La Niña that made 2008 the coolest year of its decade - while still leaving it warmer than almost every year of the 20th century, an early lesson in how the warming trend rides through the cycle.
- Two Category 5 Atlantic hurricane landfalls in 2007 (Dean, Felix)
- Deepened the US Southeast drought; record 2008 US Midwest floods
- Sharpened the 2007-08 global food price stress
Most reliable footprint: Botswana ran -1.5°C that winter - ENSO alone explains ~44% of its year-to-year swing.
1998-2001 La Niña
strong -1.7/-1.7°C (RONI/ONI)A multi-year ("triple-dip-style") La Niña following the 1997-98 El Niño. Hyperactive Atlantic hurricane seasons.
- 1998 Hurricane Mitch (~11,000 dead in C. America)
- Sahel & Horn-of-Africa drought
- Strong Indian monsoon years
Most reliable footprint: Zimbabwe ran -1.3°C that winter - ENSO alone explains ~45% of its year-to-year swing.
1997-1998 El Niño
very strong +2.4/+2.4°C (RONI/ONI)One of the most extreme El Niños of the 20th century. Briefly pushed global temperatures to a new record and caused widespread climate dislocation.
- Indonesian peatland fires & haze (~1Gt CO₂ emitted)
- East African short-rains floods (millions displaced)
- California floods & ice storms in NE US/Canada
- Coral bleaching across the Indo-Pacific
Most reliable footprint: Costa Rica ran +1.0°C that winter - ENSO alone explains ~82% of its year-to-year swing, the strongest single-country link in this entire dataset.
1991-1992 El Niño
very strong +2.3/+1.7°C (RONI/ONI)A strong El Niño by the raw index, but Mount Pinatubo’s 1991 eruption cooled the wider tropics - so on the warming-adjusted RONI scale it ranks very strong, since RONI measures Niño 3.4 against that cooler tropical background. In southern Africa it drove the region’s worst drought of the 20th century.
- Southern Africa’s 1991-92 drought - harvests halved, tens of millions needing food aid
- US West Coast storms and Texas floods
- Global temperature signal muted by Pinatubo
Most reliable footprint: Zimbabwe ran +1.8°C that winter - ENSO alone explains ~45% of its year-to-year swing, consistent with the drought this event is remembered for.
1988-1989 La Niña
strong -1.9/-1.9°C (RONI/ONI)Strong La Niña following the 1986-87 El Niño. Reinforced the 1988 US Midwest drought and helped seed an active North Atlantic hurricane season.
- 1988 US Midwest drought (US$80bn+ damages)
- Severe Sudan/Bangladesh floods
- Strong Indian monsoon recovery
Most reliable footprint: Botswana ran -2.2°C that winter - ENSO alone explains ~44% of its year-to-year swing, one of the sharpest La Niña cold snaps in the record.
1982-1983 El Niño
very strong +2.5/+2.2°C (RONI/ONI)A textbook East-Pacific El Niño that arrived almost without forecast. Caused the largest ENSO-related humanitarian crisis to that date.
- Severe Australian drought (one of worst on record)
- Indonesian forest fires & food shortages
- Catastrophic floods Peru/Ecuador
- US$13bn (1983 USD) damage worldwide
Most reliable footprint: Zimbabwe ran +2.0°C that winter - ENSO alone explains ~45% of its swing; Peru (+1.1°C) tracked even more consistently, at ~76%.
1973-1976 La Niña
strong -1.9/-2.0°C (RONI/ONI)A deep multi-year La Niña that swung straight out of the 1972-73 El Niño - one of the strongest cold events in the modern record. Its imprint marks the last time the yearly global temperature dipped close to the 20th-century average.
- Australia’s wettest year on record (1974), including Brisbane’s January flood
- Catastrophic 1974 Bangladesh monsoon floods
- Pronounced global cool dip through 1974-76
Most reliable footprint: Botswana ran -2.0°C that winter - ENSO alone explains ~44% of its year-to-year swing.
1972-1973 El Niño
very strong +2.3/+2.1°C (RONI/ONI)Arguably the most economically consequential El Niño ever. It collapsed Peru’s anchoveta fishery, then the largest fishery on Earth, and the shock cascaded through global fishmeal, soy and grain prices in an already tight world food market.
- Peruvian anchoveta catch crashed from ~12M to ~2M tonnes and never fully recovered
- Amplified the 1972-74 global food price crisis
- Drought in the Sahel, India and Australia; floods in coastal Peru
Most reliable footprint: Botswana ran +2.6°C that winter - ENSO alone explains ~44% of its year-to-year swing, one of the biggest reliably-ENSO-linked swings on record.
1965-1966 El Niño
very strong +2.0/+2.0°C (RONI/ONI)A powerful event that landed during India’s back-to-back 1965-66 monsoon failures, deepening a food crisis that pushed India into dependence on emergency grain shipments and helped trigger the Green Revolution.
- Indian monsoon failure and food crisis (the “ship-to-mouth” years)
- Drought across Indonesia and parts of Australia
- Falling anchoveta catches off Peru - an early warning before 1972
Most reliable footprint: Suriname ran +1.3°C that winter - ENSO alone explains ~55% of its year-to-year swing.
1957-1958 El Niño
very strong +2.0/+1.8°C (RONI/ONI)The first El Niño observed in scientific detail, coinciding with the International Geophysical Year measurement campaign. The data it produced seeded Bjerknes’ theory of the coupled ocean-atmosphere cycle that underpins ENSO science today.
- First event tracked by a worldwide observing network (IGY 1957-58)
- Marked North Pacific warmth and a poor Peruvian fishing season
- Weakened Indian monsoon and regional crop stress
Most reliable footprint: Panama ran +1.0°C that winter - ENSO alone explains ~79% of its year-to-year swing, one of the strongest single-country links anywhere in this dataset.
1954-1956 La Niña
strong -1.6/-1.7°C (RONI/ONI)A persistent multi-year La Niña through the mid-1950s, one of the longest cold spells on record. Remembered for hemisphere-wide drought and an exceptionally destructive stretch of Atlantic hurricanes.
- Multi-year drought across the US Southwest and southern Plains
- Destructive 1954-55 Atlantic hurricanes (Hazel, Connie, Diane)
- Deep cold anomalies across the eastern Pacific for nearly three years
Most reliable footprint: Botswana ran -1.5°C that winter - ENSO alone explains ~44% of its year-to-year swing, among the strongest links in this dataset.
Source: NOAA RONI (peak RONI + classification) and legacy ONI v5 (shown for context); country footprint figures from the same ENSO-attribution analysis used in the map above (Copernicus ERA5, GPCC/DWD precipitation, NOAA CPC).
ENSO-Driven Countries
Most & Least ENSO-Driven Countries
Ranks how much of each place’s year-to-year winter-peak (DJF) temperature or precipitation swing is explained by ENSO’s phase alone (RONI) across 1950-2025 - the same relationship behind the Footprint map’s “ENSO-expected” hover figure and Typical Impact mode. Near the top, a winter here is largely determined by El Niño or La Niña; near the bottom, hot, cold, wet or dry years are mostly ordinary weather.
Most ENSO-Driven
ENSO explains most of the swingLeast ENSO-Driven
Mostly other weather, not ENSOBy Continent
Mean of each continent's countriesSouth America
North America
Oceania
Africa
Asia
Europe
World Weather Impacts by Region
Impact on World Weather
Typical regional response per phase. Probabilities = how often the impact occurs when the phase is active.
Peru & Ecuador (coastal)
JFMS. America · Western coast of equatorial S. America
Severe coastal flooding, fisheries collapse (anchovy stocks crash as upwelling weakens). 1982-83 and 1997-98 events caused widespread infrastructure damage.
NE Brazil
JJA-DJFS. America · Sertão & northeastern coast
Major drought risk during the rainy season (Feb-May). Severe in 2015-16; agricultural and water-supply crises.
S. Brazil, Uruguay & N. Argentina
NDJS. America · La Plata basin
Wetter-than-average spring/summer; flooding along the Paraná/Uruguay rivers (e.g. 1997-98 floods).
Amazon basin
JJA-ONDS. America · Northern & central Amazonia
Drought stress, lower river levels, larger fire seasons. 2023-24 El Niño produced record-low Rio Negro levels at Manaus.
Southwest USA
DJFN. America · California, Arizona, NM, S. Nevada
Wetter winter; helps replenish reservoirs and snowpack. Strong El Niños have produced major California floods.
Pacific NW USA & W. Canada
DJFN. America · Washington, Oregon, BC, Alberta
Mild, dry winter; lower mountain snowpack. Knock-on summer wildfire risk.
Southeast USA
DJFN. America · Florida & Gulf Coast states
Wetter, cooler winter; stronger subtropical jet brings more storms.
NE USA & E. Canada
DJFN. America · Northeast US states & Maritime Canada
Milder-than-average winter; reduced heating demand.
Mexico & Central America
JJA-SONC. America · From northern Mexico to Panama
Drought risk during the rainy season (May-Oct); crop and water-supply stress, especially in the Central American Dry Corridor.
Caribbean & Atlantic basin
JJA-SONC. America · Caribbean Sea, Gulf of Mexico, tropical Atlantic
Suppresses Atlantic hurricane activity (more wind shear, drier mid-troposphere).
N. Europe (Baltic & UK)
DJFEurope · British Isles, Scandinavia, Baltic
Tendency for cooler late winters; very strong El Niños (1997-98, 1982-83) flipped the sign and gave warm winters.
Mediterranean
JJAEurope · Iberia, Italy, Balkans, N. Africa
Hotter, drier summers; heatwave and wildfire risk amplified, especially in the Iberian Peninsula.
East Africa (Horn)
ONDAfrica · Kenya, Ethiopia, Somalia, S. Sudan
"Short rains" (Oct-Dec) much wetter; flooding & locust outbreaks. 1997-98 floods displaced millions.
Southern Africa
DJFAfrica · S. Africa, Zimbabwe, Mozambique, Botswana
Major maize-belt drought; 2015-16 El Niño caused the worst SADC drought in decades. 2023-24 again triggered widespread food insecurity.
Sahel
JASAfrica · From Senegal east to Sudan
Drier West African monsoon; reduced cereal yields.
India
JJASAsia · Indian subcontinent
Weaker SW summer monsoon; ~60 % of all-India droughts since 1900 occurred in El Niño years (e.g. 2002, 2009, 2015).
Maritime SE Asia
JJA-DJFAsia · Indonesia, Malaysia, Philippines, PNG
Severe drought; major peatland & forest fires (Indonesia 1997, 2015). One of the most reliable ENSO teleconnections worldwide.
E. Asia (China, Korea, Japan)
DJFAsia · NE China, Korea, Japan
Mild winter; increased rainfall over central/E China (Yangtze flooding risk in following summer).
Eastern Australia
JJA-DJFOceania · NSW, Queensland, Victoria
Drought, heatwaves and severe bushfire seasons. Black Summer (2019-20) ran on a positive Indian Ocean Dipole + weak El Niño.
Northern Australia
DJFOceania · Top End, Cape York
Late, weaker monsoon; drought risk for cattle stations.
Central Tropical Pacific Is.
DJFPacific Is. · Kiribati, Tuvalu, Tokelau, etc.
Migration of the rain belt eastwards; severe coral bleaching during strong events (1998, 2016, 2024).
SW Pacific (Fiji, Vanuatu, NC)
DJFPacific Is. · Fiji, Vanuatu, Samoa, New Caledonia
Drought; tropical cyclones shift further east toward French Polynesia.
Sources: Met Office GPC ENSO impacts maps (Davey et al. 2013); NOAA CPC ENSO composites and historical analyses; IPCC AR6 WGI Annex VI (ENSO regional teleconnections).
Pacific-North American Pattern
Pacific-North American Pattern - Neutral
PNA is the standing wave train across the North Pacific and North America that transmits the tropical ENSO signal towards the Atlantic. +PNA (deep Aleutian Low + ridge over western North America + trough over eastern US) tends to follow El Niño; -PNA tends to follow La Niña. It is the missing link between the ENSO engine in the tropical Pacific and the NAO gatekeeper over the North Atlantic.
PNA - today
-0.17
Neutral · 2026-07-31
30-day rolling mean
last monthly +0.61 · 2026-07
Last sign flip
2026-07-11
positive → negative, sustained 5+ days
+PNA (the El-Niño-favoured pattern) means a deep Aleutian Low, a ridge over western North America (dry/warm western US, dry Pacific NW) and a trough over the eastern US (cold/snow). -PNA (La-Niña-favoured) flips all of these: warm/dry eastern US, cooler/wetter western US, and a more zonal jet that often phases with the North Atlantic to set up -NAO blocking patterns. Data: NOAA CPC daily PNA.
ENSO and Climate Change
ENSO & Climate Change
ENSO is a natural cycle that has run for thousands of years (proven by coral and tree-ring records). Human-driven warming acts as a force multiplier - elevated tropical-ocean heat now combines with every El Niño, sharpening droughts, floods, heatwaves and record-breaking global temperatures.
Intensification of Extremes
ENSO is a natural cycle, but climate change acts as a force multiplier. Higher global temperatures are deepening El Niño droughts in Australia, Brazil and the Amazon, and driving heavier rainfall across the southern US and East Africa - the same teleconnection patterns, but with sharper edges.
More Frequent, More Intense Events
Warmer sea-surface temperatures favour more rapid ENSO development and a higher occurrence of strong El Niño events. IPCC AR6 (2021) found with high confidence that ENSO SST variability over the past 50 years has been larger than at any time in the previous 400.
Temperature Records Stack Up
Every El Niño now releases its heat onto a baseline already ~1.3°C above pre-industrial. The 1997-98, 2015-16 and 2023-24 events each set new global temperature records; 2024 became the first calendar year above 1.5°C. Without continued greenhouse-gas warming the same ENSO events would have produced much smaller spikes.
La Niña No Longer Cools Below the Trend
Strong La Niña years used to deliver global mean temperatures below the long-term average. Today, even the deepest La Niñas (2020-22) sit well above any 20th-century year. La Niña now buys a temporary pause in record-breaking - it does not reverse the warming.
Oceans and Sea Ice Take a Hit
Warmer ocean waters combined with ENSO trigger more widespread coral bleaching and deeper marine heatwaves. The atmospheric changes also push warmer water to higher latitudes, helping to reduce Arctic sea ice during strong El Niño years.
A More Volatile Climate System
An accelerated Hadley circulation during El Niño, combined with a warmer atmosphere holding ~7% more moisture per °C, is making compound extremes harder to predict. Most CMIP6 models project ENSO rainfall variability will increase with further warming - bigger droughts and bigger floods in the same teleconnection regions.
Sources: IPCC AR6 WGI Chapter 4, Box TS.13; Grothe et al. 2020 (coral records of ENSO amplification); Cai et al. 2021 (Nature Climate Change).
Explore Climate Data
Explore Climate Data
Methodology & Data Sources
Methodology & Sources
- Oceanic Niño Index (ONI) - 3-month running mean of ERSSTv5 SST anomalies in the Niño 3.4 box (5°S–5°N, 170°W–120°W) relative to a centred 30-year base period that updates every 5 years. NOAA's official ENSO yardstick.
- Relative Oceanic Niño Index (RONI) - NOAA's official ENSO index since Feb 2026, and the single classification/record/forecast basis used throughout this site. RONI scales the raw Niño 3.4 anomaly by a monthly factor (~1.1 in Jul–Aug to ~1.4 in Mar–Apr) after subtracting the tropical-mean (20°N–20°S) SST anomaly, so a warming background ocean does not by itself inflate ENSO strength. Raw ONI is retained alongside RONI as a secondary figure. Stockdale (2026, ECMWF Science Blog).
- Weekly Niño-region SSTs - OISSTv2-based weekly mean SST and SST anomaly (1991–2020 baseline) for Niño 1+2, 3, 3.4 and 4.
- Multivariate ENSO Index v2 - bi-monthly principal- component combination of SST, sea-level pressure, zonal & meridional surface winds and outgoing longwave radiation over the tropical Pacific. Captures atmospheric coupling.
- Southern Oscillation Index - standardised difference in sea-level pressure between Tahiti and Darwin. The classical atmospheric measure of ENSO; persistent negative SOI accompanies El Niño.
- NOAA CPC strength probabilities - monthly official odds of each strength category (weak / moderate / strong / very strong per phase) using RONI thresholds. Shown as shading in the season-by-season probability bars.
- AI briefing - generated by Gemini, grounded in this page's own data plus a curated regional impact matrix (Met Office GPC / Davey et al. 2013 / NOAA composites), documented consequences of comparable past events, this month's country-level temperature anomalies, and active extreme weather (GDACS) - with search grounding for recent expert commentary. The "early signs" table beneath the briefing - comparing each named region's current temperature anomaly against its historically expected signal - is computed entirely in code, not by the AI: it's handed a finished fact, not asked to work it out. Cached and regenerated when new weekly observations or a new monthly forecast issuance arrive.
Snapshot generated Mon, 07 Sep 2026 04:24:50 GMT. Refreshed monthly.
FAQs
El Niño & La Niña: Common Questions
Is El Niño or La Niña active right now?
The current ENSO state is shown live at the top of this page, derived from the NOAA Climate Prediction Center's Relative Oceanic Niño Index (RONI) - the primary ENSO index since Feb 2026, alongside the legacy Oceanic Niño Index (ONI) for continuity. El Niño is declared when the 3-month running mean stays at or above +0.5°C (+0.9°F) for five overlapping seasons; La Niña uses the mirror threshold of -0.5°C (-0.9°F). Otherwise the Pacific is classed as Neutral.
What is RONI, and how is it different from ONI?
RONI (the Relative Oceanic Niño Index) is NOAA's official ENSO index since February 2026. Like the older ONI (Oceanic Niño Index), it measures the sea-surface temperature (SST) anomaly in the Niño 3.4 region of the tropical Pacific - but RONI first subtracts the average warming across the whole tropical ocean belt (20°N-20°S) and then rescales the result to match ONI's amplitude. That removes the background global-warming signal, so a modern El Niño is judged on a like-for-like yardstick against events from the 1980s and 1990s rather than being inflated by decades of ocean warming. In practice RONI runs a few tenths of a degree below ONI for recent El Niños: the 2023-24 event was 'very strong' on ONI (peak +2.0°C / +3.6°F) but 'strong' on RONI (+1.5°C / +2.7°F), and the strongest event on the RONI record is 1982-83 (about +2.5°C / +4.5°F), not 2015-16. This page classifies current state, strength, records and forecasts on RONI, and shows ONI alongside for continuity.
What are El Niño and La Niña, and which countries do they affect?
El Niño is the warm phase of the El Niño-Southern Oscillation (ENSO). It typically brings heavier rain and floods to the western coast of South America (Peru, Ecuador), the southern United States and parts of East Africa, while causing drought across Indonesia, Australia, the Philippines, southern Africa and the Amazon. La Niña, the cool phase, broadly flips these: wetter conditions in Australia, Indonesia and southern Africa, drier conditions in the southern US and the Horn of Africa. Both phases shift global average temperatures by roughly +0.1 to +0.2°C (+0.18 to +0.36°F) and now sit on top of the long-term climate-change warming trend.
Which countries are most affected by El Niño?
El Niño typically brings heavier rainfall and flooding to Peru, Ecuador, the southern United States and parts of East Africa (Kenya, Tanzania, Somalia). It causes drought across Indonesia, Australia, the Philippines, Papua New Guinea, southern Africa (Zimbabwe, South Africa, Mozambique) and the Amazon basin. Northern South America (Colombia, Venezuela) and the Caribbean tend to be drier than average.
Which countries are most affected by La Niña?
La Niña broadly flips the El Niño pattern. It brings wetter conditions to Australia, Indonesia, the Philippines, southern Africa and the Amazon, but drought to the Horn of Africa (Somalia, Ethiopia, Kenya), the southern United States, Argentina, Uruguay and southern Brazil. La Niña also boosts Atlantic hurricane activity and tends to suppress eastern-Pacific hurricanes.
What is the difference between El Niño and La Niña?
They are opposite phases of the same Pacific climate cycle (ENSO). El Niño is the warm phase: equatorial Pacific surface waters are 0.5°C (0.9°F) or more above average, trade winds weaken, and global average temperatures briefly rise. La Niña is the cool phase: Pacific waters are 0.5°C (0.9°F) or more below average, trade winds strengthen and global temperatures briefly dip. Each phase lasts roughly 9-18 months and they alternate (with Neutral years) on a 2-7 year cycle.
Why does El Niño cause floods in some places and drought in others?
During El Niño the warm pool of water that normally sits in the western Pacific shifts eastward toward South America. Atmospheric convection - the rising air that produces rain - follows it. So Indonesia and Australia, which usually sit under that rising air, lose their rainfall, while Peru and Ecuador get downpours from convection that has moved over them. The shift also rearranges global jet streams, which is why effects show up as far away as East Africa and the southern US.
How is ENSO different from climate change?
ENSO is a natural redistribution of heat between the tropical Pacific Ocean and the atmosphere on a 2-7 year cycle. It can boost or suppress global temperatures by 0.1-0.3 °C (0.18-0.54 °F) for a year or two. Climate change is the long-term warming trend driven by greenhouse gases. Record-warm years (2016, 2023, 2024) typically combine a strong El Niño on top of the long-term trend.
When was the last major El Niño?
The most recent El Niño peaked in late 2023 / early 2024 with a peak RONI around +1.5°C (+2.7°F), classed as a strong event. Combined with long-term warming it helped push 2023 and 2024 to record-warm globally. Other recent strong El Niños were 2015-16 and 1997-98, historically among the most intense on record - though under RONI, NOAA's trend-adjusted measure, 1982-83 rates comparably or even slightly stronger once background tropical warming is factored out of all three. The most recent prolonged La Niña was the rare triple-dip event of 2020-23.
What is the Niño 3.4 region?
Niño 3.4 is a box across the central tropical Pacific (5°N-5°S, 170°W-120°W). Its sea-surface temperature anomaly is the standard index used by NOAA, WMO and most climate agencies to define ENSO state. Niño 1+2 (off Peru), Niño 3 (eastern Pacific) and Niño 4 (western/central Pacific) are also tracked here for context.
Where does the data come from?
Indicators are pulled directly from NOAA: the CPC Relative Oceanic Niño Index (RONI, primary since Feb 2026) and the legacy Oceanic Niño Index (ONI), CPC weekly Niño-region SSTs, NOAA Physical Sciences Lab MEI v2 and CPC Southern Oscillation Index (SOI). The probability forecast is the NOAA CPC official outlook, itself RONI-based. The magnitude forecast curve (median plus a percentile range) is NOAA CPC's own official RONI outlook, alongside the SNU ACE Lab CNN forecast (Ham et al. 2019). Regional teleconnection patterns are based on Met Office GPC composites and Davey et al. (2013). RONI methodology: Stockdale (2026, ECMWF Science Blog), Van Oldenborgh et al. (2021, Environmental Research Letters 16, 044003) and L'Heureux et al. (2024, Journal of Climate 37(4), 1197-1211).
How often is the tracker updated?
Weekly. The Niño-region SST anomalies update every Monday on NOAA CPC. The RONI and ONI 3-month indices update monthly, the MEI v2 every two months. We rebuild the snapshot used by this page once a week.
Can journalists cite, embed or reuse this data?
Yes. Every figure on this page traces back to a named NOAA, IRI or academic source (see "Where does the data come from?" above), so it can be cited directly rather than screenshotted. Charts and cards - the current-state readout, the strongest-events ranking, the forecast-evolution history and the country impact tool - each have a share button that generates an embeddable iframe plus a pre-filled citation link, and the underlying forecast archive is public JSON at /data/climate/enso-forecast-archive.json. Figures are labelled RONI or ONI explicitly throughout, so a reporter can state which index a number uses without having to work it out themselves.
How strong will the coming El Niño be?
Strength is a probability, not a certainty. NOAA CPC publishes official strength probabilities using RONI thresholds - weak (0.5-1.0°C), moderate (1.0-1.5°C), strong (1.5-2.0°C) and very strong (2.0°C or more) - and this page shades its season-by-season probability bars with those odds, updated monthly. NOAA's own official RONI outlook (median plus a percentile range) and the SNU CNN AI model add magnitude forecasts of the peak Niño 3.4 anomaly. Note that model skill at record-breaking magnitudes is unproven: no forecast this extreme has been verified before.
How have the forecasts for this El Niño changed over time?
This page keeps an archive of every monthly forecast issuance (NOAA CPC probabilities and strength odds, the IRI/CCSR plume, and the SNU CNN AI forecast) and charts how the predicted peak has evolved. During 2026 the AI model called a 3°C-class event from April onward, while the physics-based multi-model plume and the official NOAA strength odds climbed towards it issuance by issuance. The raw archive is public JSON at /data/climate/enso-forecast-archive.json.
Does this tracker use AI to forecast El Niño, and how reliable is it?
We show two kinds of forecast side by side and let you compare them. The traditional approach is physics-based: NOAA CPC's official strength-probability outlook and its official RONI outlook (a ~10-person team's consolidated median-plus-range synthesis of many models and current observations). Alongside it we track a deep-learning AI forecast - Seoul National University's convolutional neural network (Ham et al. 2019, Nature) - which is trained on past ocean patterns and can skilfully predict Niño 3.4 up to 18-24 months ahead. Our forecast-evolution archive records every monthly issuance, so you can see how the AI model's and the physics-based forecasts' peak calls have moved relative to each other over the course of this event - an example of AI-based and traditional forecasting compared side by side. We report all of this factually and grounded in published NOAA data rather than hype, and we note openly that no forecast model's skill at record-breaking magnitudes has been verified, so peak values remain uncertain.
Why has the ranking of the strongest El Niño events changed under RONI?
Because RONI removes the background warming of the wider tropical ocean, it changes how events compare across the decades. Older events happened against a cooler tropical background, so RONI lifts them; recent events happened against a warmer background, so RONI trims them back towards the ENSO signal itself. That reshuffles the record: on RONI the strongest El Niño since 1950 is 1982-83 (about +2.5°C / +4.5°F), ahead of 1997-98 and 2015-16 (about +2.4°C / +4.3°F each), whereas on the raw ONI the warmer-baseline 2015-16 tops the list (+2.8°C). Individual events move too - 2023-24 drops from 'very strong' on ONI to 'strong' on RONI, while 1991-92 is lifted to 'very strong' because the Mount Pinatubo eruption had cooled the surrounding tropics that year. It is the same ocean data: RONI simply measures each El Niño against the climate of its own time, rather than letting decades of global warming inflate the more recent ones.
Could this be the strongest El Niño ever recorded? What is the strongest on record?
It depends on the yardstick. On NOAA's official RONI index - which subtracts the tropical-mean ocean warming to isolate the ENSO signal itself - the strongest El Niño on record since 1950 is 1982-83, at a peak of about +2.5°C (+4.5°F), ahead of 1997-98 and 2015-16 (both about +2.4°C / +4.3°F). In raw Niño 3.4 (ONI) terms 2015-16 tops the list (+2.8°C) partly because the ocean baseline is warmer than in the 1980s or 1990s, which is exactly the inflation RONI removes. A new record is therefore more plausible on raw ONI than on RONI; this page ranks the strongest events on record by peak RONI and shows the raw ONI peak alongside, plus the latest forecast, so you can judge both framings.