Niño 3.4 anomaly
A sea surface temperature anomaly for 5°N–5°S, 170°W–120°W. The weekly CPC series uses the 1991–2020 reference climatology. A weekly reading does not establish an official ENSO phase.
TRANSPARENT BY DESIGN
Know what you're looking at.
The sources, the distinctions, and the limits behind the numbers.
Different numbers answer different questions.
RONI
The Relative Oceanic Niño Index adjusts for tropical ocean background warming and uses a three-month window. CPC currently publishes ERSSTv6 RONI values against a 1991–2020 reference. Points appear at the end of each season; they are not weekly observations.
ONI
The Oceanic Niño Index is a conventional three-month Niño 3.4 anomaly. It is not the weekly anomaly or RONI. ENSOLens charts RONI, and its probability table follows CPC's RONI-based framework.
Go back to the source.
CPC ENSO Diagnostics DiscussionOfficial phase, alert, synopsis, and release dates
CPC weekly Niño-region SSTWeekly Niño 3.4 anomaly · 1991–2020 reference climatology
CPC Relative Oceanic Niño IndexThree-month RONI · ERSSTv6 and 1991–2020 reference
CPC ENSO probabilitiesMonthly issue · three-month RONI-based target seasons
CPC sea surface temperature figureOriginal NOAA image · dates and scale retained
Keep the dates and uncertainty visible.
Scheduled checks, dated observations.
Sources are checked every six hours. This is a retrieval schedule, not the publication frequency of NOAA data. Each feed retains its own issue or observation date and retrieval time. Weekly anomalies and seasonal RONI are plotted on their own dates.
Validation checks source formats, dates, value ranges, and probability totals. If a source fails, its last validated data remains available and a notice appears. Checks delayed more than two days, overdue publications, and source failures are reported on the data status endpoint.
Compare identical target seasons.
Forecast comparison matches the same three-month season and year across issues. Missing target seasons remain blank. Monthly forecast revisions and map versions are retained, and CSV downloads identify the source series or forecast issue.
Probability is not impact severity. An ENSO phase probability is not a probability of flooding, snow, crop damage, or hurricane landfall. Regional pages describe historical tendencies, not current local forecasts.
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ENSOLens republishes official data with independent presentation and context. It is not affiliated with NOAA, CPC, or the U.S. government. See publisher information and privacy.