Plain-language glossary
Short labels keep the instrument compact. This guide explains both the acronyms and the science terms in everyday language.
A three-month El Niño index adjusted for the average warming of the tropics.
The Pacific ocean–atmosphere cycle that includes El Niño, neutral, and La Niña phases.
Scientists average ocean temperatures in this region because persistent warmth here is a reliable core signal of El Niño.
A +1°C anomaly means the reading is one degree warmer than the chosen average, not that the water itself is 1°C.
Its depth helps show where warm water is stored below the Pacific surface.
Ocean-surface temperature, or its difference from a long-term average.
The US climate center that publishes the official outlooks used here.
NOAA's daily global sea-surface temperature analysis.
A satellite-derived clue to tropical cloud and thunderstorm activity.
An atmospheric pressure index used to track whether the atmosphere is coupled to El Niño.
May–July and October–December. Climate outlooks use these compact season labels.
The low, median, and high points of a forecast range. P50 is the midpoint, not a certainty.
A pressure unit. 850 hPa is a lower-atmosphere level used to monitor trade winds.
What is El Niño?
El Niño begins when the central and eastern tropical Pacific stay unusually warm and the atmosphere responds. Scientists look at the ocean, trade winds, tropical storms, air pressure, and heat below the surface together.
SOURCE · NOAA ENSO overview ↗What is RONI?
The Relative Oceanic Niño Index measures a three-month change in the Niño 3.4 region after accounting for average tropical warming. El Neenyo uses it to compare the current event, forecasts, and past events. Recent values are provisional and can change.
SOURCE · NOAA CPC Relative Oceanic Niño Index ↗Standard vs relative sea temperature
The standard measure compares local sea-surface temperature with the 1991–2020 average. The relative measure also removes the average temperature change across the tropics. RONI is a three-month relative measure. These numbers answer different questions and should not be swapped.
SOURCE · NOAA CPC Weekly Relative Niño Regions ↗Why RONI lags the weekly number
The weekly Niño 3.4 number is a recent ocean reading. RONI covers three months, so it changes more slowly and may be revised. A forecast describes a range of possible future values. The numbers can differ because they cover different periods.
SOURCE · NOAA CPC RONI Outlook ↗What ‘very strong’ means
NOAA calls an event “very strong” when the three-month RONI reaches at least +2.0°C. The forecast gives the chance of crossing that line. It is not a current reading and does not guarantee severe effects in a particular place.
SOURCE · NOAA CPC ENSO Strength Probabilities ↗What ‘historic’ means
El Neenyo shows a historic-threshold watch only when NOAA publishes the season, threshold, and probability. It means an unusual level is possible. It does not mean a record has already happened.
SOURCE · NOAA CPC ENSO Diagnostic Discussion ↗How the ocean and atmosphere reinforce each other
When the trade winds weaken, warm surface water can spread east. Warm water below the surface also shifts east, and tropical storms follow the warmer water. These changes can strengthen one another. The Engine shows each measurement separately instead of combining them into a made-up score.
SOURCE · NOAA GODAS Equatorial Pacific Temperature ↗Why El Niño can affect faraway regions
Past El Niño events have repeatedly shifted the odds of rain, heat, drought, fire, and storms in distant regions. A past pattern is not a local forecast. A measured change does not prove El Niño caused it, and a stronger event does not guarantee a worse local outcome.
SOURCE · NOAA CPC global patterns ↗Data freshness
“Data updated” means a scientific source published a meaningful change. “Last checked” only means the site reached the source successfully. “Newest observation” is the date of the latest measurement. News never changes the scientific update time.
Revision policy
El Neenyo keeps the source response, reading date, code version, and revision history. Recent RONI values are marked provisional. If a source cannot be read, the site shows an error or stale label and keeps the last valid value; it never replaces the value with zero.
Data sources
These are the agencies and datasets behind the site. News has its own clock and does not change the scientific update time.
Independent project
El Neenyo is an independent visualization project and is not affiliated with NOAA or any national meteorological agency. It is not an emergency-warning service. Use official local authorities for safety-critical decisions.