Guide

Relative Oceanic Niño Index (RONI)

The Relative Oceanic Niño Index (RONI) is NOAA’s seasonal ENSO index. It is a three-month average of the Niño 3.4 sea surface temperature anomaly, adjusted for the temperature anomaly of the wider tropics and rescaled. NOAA publishes one new overlapping season each month. The latest published value is +1.4 °C for JJA 2026, covering 1 June 2026 to 31 August 2026.

Latest seasonal RONI value on ENSO Tracker
Season	Period	Central month	Value	Dataset
JJA 2026	1 June 2026 – 31 August 2026	July 2026	+1.4 °C	Relative ERSST v6

1991–2020 baseline. Retrieved 16 September 2026. NOAA may revise the two most recent seasons when later data arrive, so treat the latest value as provisional.

Open the seasonal RONI record →

What RONI measures

RONI starts from the monthly Niño 3.4 sea surface temperature anomaly in NOAA’s Relative ERSST v6 dataset, measured against the 1991–2020 average. The anomaly averaged across the tropical oceans for the same month is subtracted, so that warmth or cooling shared by the whole tropical belt does not count as an ENSO signal. The result is rescaled so its variability stays comparable with the conventional index, then averaged over three consecutive months. The full definition, including the rescaling step, is in NOAA’s RONI information circular ↗. A conceptual description is enough for reading the chart: RONI asks how unusual Niño 3.4 is relative to the rest of the tropics, not relative to a fixed past.

Reading the season labels

Each RONI value carries a three-letter label made from the initials of its three months. The season belongs to the year of its central month. Two seasons cross a calendar year boundary, and their labels are the ones most often misread: DJF 1950 is December 1949 to February 1950, while NDJ 1950 is November 1950 to January 1951. The current season, JJA 2026, runs from 1 June 2026 to 31 August 2026; that interval comes from the published period dates, not from the label alone.

The twelve overlapping RONI seasons
Label	Months	Central month
DJF	December – February	January
JFM	January – March	February
FMA	February – April	March
MAM	March – May	April
AMJ	April – June	May
MJJ	May – July	June
JJA	June – August	July
JAS	July – September	August
ASO	August – October	September
SON	September – November	October
OND	October – December	November
NDJ	November – January	December

DJF begins in the previous calendar year and NDJ ends in the following one. Consecutive seasons share two of their three months, so neighbouring values are not independent observations.

How RONI relates to weekly Niño 3.4

RONI and the weekly Niño 3.4 anomalies describe the same region but are different products. The weekly series comes from a satellite-based daily analysis published every week; RONI comes from a monthly reconstructed dataset published once a month. Averaging this site’s weekly relative anomalies over three months does not reproduce RONI, and the site does not attempt it. There is no weekly RONI. When the weekly chart and the seasonal value point in the same direction, that is useful corroboration; when they do not, the difference usually reflects timing, since the newest season ends weeks before the latest weekly observation.

Thresholds and episode classification

The RONI chart marks reference lines at +0.5 °C and −0.5 °C. A season beyond one of those lines is shaded red or blue, but shading is not a diagnosis. NOAA’s historical table classifies an El Niño or La Niña episode only when the index stays at or beyond the threshold for at least five consecutive overlapping seasons. A single warm season, or two, can occur without an episode being recognised. The current operational phase is separate again: it comes from NOAA’s monthly ENSO Diagnostic Discussion, which weighs the ocean, the atmosphere and expected persistence. That assessment is what the homepage status reports.

Revisions and provenance

NOAA’s monthly dataset is updated as late observations arrive, so the two most recent RONI seasons can change after first publication. ENSO Tracker keeps every retrieved archive with its checksum and records any changed values against the previous archive; the latest value on this page should therefore be read as the value published at the retrieval time shown above. If a new file fails validation, the previously validated dataset stays in use. Missing or unpublished seasons stay blank in the chart rather than being filled with zero. Details are in the methodology.

Exploring the record

The seasonal record runs from DJF 1950 to JJA 2026, 919 values in all. The record view shows the whole series on one time axis, with the shaded seasons making long warm and cool spells easy to spot. The comparison view lines up years by season label so you can compare how this year’s seasons are evolving against selected past years. Hover or tap a point for the full period dates and the value at source precision.