Overview

The Nino 3.4 sea-surface-temperature anomaly expressed relative to the tropical-mean SST anomaly, published monthly by the NOAA Climate Prediction Center as overlapping three-month windows.

#enso #roni #sea surface temperature #climate index #seasonal forecasting

Important note

CPC REVISES PAST VALUES, so a refetch changes history - pin and record the fetch date with any analysis. RONI differs from the Nino 3.4 anomaly by up to 0.567 degC on a time-trending gap (about +0.20 degC in 1981-1995 falling to about -0.30 degC in 2015-2025), so mixing RONI and Nino 3.4 in one analogue-season comparison biases matches toward older years. Values are three-month means labelled by their centre month.

Intended uses

classifying seasons by ENSO phase (El Nino, La Nina, neutral)
selecting analogue years for seasonal outlooks and impact analysis
ENSO driver for rainfall, drought and crop anomaly studies

Not recommended for

Mixing RONI with the raw Nino 3.4 anomaly in one time series or distance metric.

Why: The two differ by up to 0.567 degC and the gap trends over time, so a mixed series biases analogue matching toward older years.

Use instead: One index end to end, RONI throughout.

Access & use

Files, endpoints, and worked examples for each distribution.

Data

roni-ascii

Fixed-width ASCII table, one row per overlapping three-month window.

Format: text/plain

Variables: ANOM

Dimensions: SEAS × YR

Data dictionary →

Access the dataOpen

https://www.cpc.ncep.noaa.gov/data/indices/RONI.ascii.txt

Data dictionary

What each file holds. A layout describes how the data is stored in a file: its variables, the dimensions they vary over, and any keys.

File layouts

Files	Format	Variables	Dimensions
roni-ascii	text/plain	ANOM	SEAS × YR

Variables

Variable	Type	Unit	Description
ANOM	number	degC	Relative Oceanic Nino Index: the Nino 3.4 SST anomaly minus the tropical-mean (20S-20N) SST anomaly, averaged over the three-month window.

Dimensions

SEASseason

Overlapping three-month window named by the initials of its months (DJF = Dec-Feb ... NDJ = Nov-Jan), labelled by its centre month.

Type: string

DJF
JFM
FMA
MAM
AMJ
MJJ
JJA
JAS
ASO
SON
OND
NDJ

YRtemporal

Calendar year of the window's centre month.

Type: integer

Technical metadata

The full spatial, temporal, and modeling detail behind the summaries elsewhere on this page.

Temporal

Start: 1950-01
End: open (present)
Updates: Monthly

How to cite

Please cite the dataset and any associated peer-reviewed publications.

NOAA Climate Prediction Center (2026) Relative Oceanic Nino Index (RONI). Version 1. NOAA National Weather Service, Climate Prediction Center. https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso/roni/. Accessed through the CGIAR Climate Action Data Hub, https://cgiar-climate-data-hub.github.io/catalog/enso-driver-roni_1/.

BibTeX

@misc{enso_driver_roni_2026,
  title     = {Relative Oceanic Nino Index (RONI)},
  author    = {{NOAA Climate Prediction Center}},
  year      = {2026},
  version   = {1},
  publisher = {NOAA National Weather Service, Climate Prediction Center},
  url       = {https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso/roni/},
  note      = {Accessed through the CGIAR Climate Action Data Hub, https://cgiar-climate-data-hub.github.io/catalog/enso-driver-roni_1/}
}

Contacts

Who produced this dataset, and who to reach about it.

Peter StewardMaintainer

Alliance of Bioversity International and CIAT

Point of contact

p.steward@cgiar.org

Brayden YoungbergMaintainer

Alliance of Bioversity International and CIAT

b.youngberg@cgiar.org

NOAA Climate Prediction CenterLicensor

Producer

NOAA CPC Relative Oceanic Nino Index (RONI)