The Relative Oceanic Niño Index (RONI) is now NOAA’s official ENSO classification index for tracking El Niño (warm) and La Niña (cool) events in the eastern tropical Pacific. RONI is defined as the running 3-month mean of ERSST.v5 sea surface temperature (SST) anomalies in the Niño 3.4 region (5°N–5°S, 120°–170°W), with the average tropical mean (20°N–20°S) SST anomaly subtracted. The resulting difference is then adjusted so that its variance matches that of the original Niño 3.4 index. Events are classified when anomalies persist for at least five consecutive overlapping 3-month periods, exceeding +0.5°C for El Niño and falling below −0.5°C for La Niña.
Why RONI Was Introduced
The introduction of the Relative Oceanic Niño Index (RONI) addresses a fundamental limitation in traditional ENSO indices such as the Oceanic Niño Index (ONI): their inability to fully account for long-term warming of the tropical oceans. ONI is based solely on sea surface temperature (SST) anomalies in the Niño 3.4 region relative to a fixed or stepwise-updated climatology. As global temperatures rise, the background state of the oceans also warms, which can artificially enhance or suppress ENSO signals when viewed in isolation.
RONI resolves this issue by expressing Niño 3.4 anomalies relative to the broader tropical mean (20°N–20°S). By subtracting the average tropical SST anomaly, RONI effectively removes the global warming signal and isolates the relative temperature contrast that drives atmospheric circulation changes associated with ENSO. This makes RONI a more dynamically consistent measure of ENSO, focusing on the gradient between the eastern-central Pacific and the surrounding tropics rather than absolute temperatures alone.
As a result, RONI provides a more stable and physically meaningful framework for identifying El Niño and La Niña events in a warming climate, reducing the risk of misclassification and improving consistency across decades.
ENSO Alert System Status: La Niña Advisory / El Niño Watch
La Niña is present.*
Equatorial sea surface temperatures (SSTs) are near-to-below-average in the east-central Pacific Ocean. Atmospheric anomalies over the tropical Pacific Ocean are consistent with La Niña.
A transition from La Niña to ENSO-neutral is expected in the next month, with ENSO-neutral favored through May-July 2026 (55% chance). In June-August 2026, El Niño is likely to emerge (62% chance) and persist through at least the end of 2026.*
Note: Statements are updated once a month (2nd Thursday of each month) in association with the ENSO Diagnostics Discussion, which can be found by clicking here.
RNino3.4 SST Anomaly YR MTH ANOM 2025 1 -1.29 2025 2 -0.98 2025 3 -0.44 2025 4 -0.59 2025 5 -0.54 2025 6 -0.33 2025 7 -0.41 2025 8 -0.69 2025 9 -0.81 2025 10 -0.81 2025 11 -0.99 2025 12 -0.99 2026 1 -0.93 2026 2 -0.72 2026 3 -0.51
| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1950 | -1.5 | -1.3 | -1.1 | -1.1 | -1.0 | -0.7 | -0.4 | -0.2 | -0.2 | -0.3 | -0.4 | -0.6 |
| 1951 | -0.5 | -0.2 | 0.3 | 0.6 | 0.6 | 0.7 | 0.7 | 0.8 | 0.9 | 1.0 | 0.9 | 0.8 |
| 1952 | 0.6 | 0.4 | 0.4 | 0.4 | 0.3 | 0.1 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.2 |
| 1953 | 0.5 | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 | 0.7 | 0.7 | 0.7 | 0.8 | 0.8 | 0.9 |
| 1954 | 1.0 | 0.7 | 0.1 | -0.2 | -0.3 | -0.3 | -0.5 | -0.7 | -0.8 | -0.7 | -0.6 | -0.4 |
| 1955 | -0.4 | -0.3 | -0.3 | -0.4 | -0.4 | -0.4 | -0.4 | -0.6 | -1.0 | -1.4 | -1.6 | -1.3 |
| 1956 | -0.7 | -0.3 | -0.2 | -0.1 | 0.0 | -0.1 | -0.3 | -0.3 | -0.3 | -0.3 | -0.4 | -0.2 |
| 1957 | 0.0 | 0.4 | 0.7 | 1.0 | 1.1 | 1.2 | 1.2 | 1.3 | 1.2 | 1.3 | 1.5 | 1.9 |
| 1958 | 2.0 | 1.9 | 1.4 | 1.1 | 0.8 | 0.7 | 0.5 | 0.3 | 0.2 | 0.3 | 0.4 | 0.7 |
| 1959 | 0.8 | 0.8 | 0.7 | 0.4 | 0.3 | -0.1 | -0.2 | -0.4 | -0.3 | -0.3 | -0.1 | 0.0 |
| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| 1960 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.0 | 0.1 | 0.2 | 0.2 | 0.1 | 0.0 | 0.0 |
| 1961 | 0.1 | 0.1 | 0.0 | 0.1 | 0.3 | 0.3 | 0.2 | -0.1 | -0.3 | -0.3 | -0.2 | -0.1 |
| 1962 | -0.1 | -0.1 | -0.1 | -0.2 | -0.3 | -0.2 | -0.1 | -0.2 | -0.2 | -0.4 | -0.5 | -0.5 |
| 1963 | -0.4 | -0.1 | 0.2 | 0.2 | 0.2 | 0.4 | 0.7 | 1.0 | 1.0 | 1.1 | 1.2 | 1.3 |
| 1964 | 1.1 | 0.7 | 0.1 | -0.4 | -0.6 | -0.6 | -0.6 | -0.6 | -0.7 | -0.8 | -0.7 | -0.5 |
| 1965 | -0.2 | 0.1 | 0.2 | 0.4 | 0.6 | 1.0 | 1.4 | 1.7 | 1.9 | 2.0 | 2.0 | 1.9 |
| 1966 | 1.7 | 1.5 | 1.3 | 0.9 | 0.5 | 0.3 | 0.3 | 0.1 | 0.0 | -0.1 | -0.1 | -0.2 |
| 1967 | -0.2 | -0.2 | -0.4 | -0.4 | -0.2 | 0.2 | 0.3 | 0.1 | 0.0 | -0.1 | 0.0 | 0.0 |
| 1968 | -0.2 | -0.3 | -0.3 | -0.2 | 0.2 | 0.5 | 0.7 | 0.6 | 0.5 | 0.6 | 0.8 | 1.1 |
| 1969 | 1.2 | 1.1 | 0.9 | 0.5 | 0.4 | 0.2 | 0.2 | 0.4 | 0.7 | 0.8 | 0.7 | 0.6 |
| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| 1970 | 0.5 | 0.3 | 0.3 | 0.1 | 0.0 | -0.3 | -0.6 | -0.7 | -0.7 | -0.6 | -0.7 | -0.9 |
| 1971 | -1.0 | -1.0 | -0.8 | -0.6 | -0.5 | -0.4 | -0.4 | -0.4 | -0.5 | -0.5 | -0.5 | -0.5 |
| 1972 | -0.3 | 0.0 | 0.4 | 0.8 | 0.9 | 1.1 | 1.3 | 1.5 | 1.7 | 2.0 | 2.2 | 2.3 |
| 1973 | 2.0 | 1.4 | 0.6 | -0.2 | -0.8 | -1.1 | -1.2 | -1.4 | -1.5 | -1.8 | -1.9 | -1.9 |
| 1974 | -1.5 | -1.2 | -0.9 | -0.9 | -0.8 | -0.6 | -0.4 | -0.2 | -0.2 | -0.4 | -0.4 | -0.2 |
| 1975 | -0.1 | -0.1 | -0.3 | -0.5 | -0.6 | -0.8 | -0.9 | -0.9 | -1.0 | -1.0 | -1.1 | -1.1 |
| 1976 | -1.0 | -0.6 | -0.3 | -0.1 | 0.0 | 0.2 | 0.5 | 0.7 | 0.9 | 1.1 | 1.1 | 1.1 |
| 1977 | 1.0 | 0.9 | 0.5 | 0.3 | 0.2 | 0.4 | 0.4 | 0.6 | 0.8 | 1.0 | 1.1 | 1.1 |
| 1978 | 0.9 | 0.6 | 0.1 | -0.2 | -0.4 | -0.3 | -0.3 | -0.3 | -0.2 | 0.0 | 0.2 | 0.2 |
| 1979 | 0.2 | 0.2 | 0.2 | 0.2 | 0.1 | -0.1 | 0.0 | 0.2 | 0.4 | 0.5 | 0.5 | 0.7 |
| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| 1980 | 0.6 | 0.5 | 0.3 | 0.2 | 0.3 | 0.3 | 0.2 | 0.0 | 0.0 | 0.1 | 0.2 | 0.2 |
| 1981 | 0.0 | -0.3 | -0.3 | -0.3 | -0.3 | -0.3 | -0.3 | -0.2 | -0.1 | -0.2 | -0.2 | 0.0 |
| 1982 | 0.1 | 0.3 | 0.4 | 0.6 | 0.8 | 0.8 | 0.9 | 1.3 | 1.8 | 2.2 | 2.4 | 2.5 |
| 1983 | 2.5 | 2.2 | 1.7 | 1.4 | 1.0 | 0.6 | 0.1 | -0.2 | -0.6 | -0.9 | -1.1 | -1.0 |
| 1984 | -0.5 | -0.3 | -0.3 | -0.5 | -0.6 | -0.4 | -0.2 | -0.1 | -0.1 | -0.5 | -0.8 | -1.0 |
| 1985 | -0.8 | -0.6 | -0.6 | -0.7 | -0.7 | -0.5 | -0.4 | -0.3 | -0.2 | -0.2 | -0.1 | -0.2 |
| 1986 | -0.3 | -0.3 | -0.2 | -0.1 | -0.1 | -0.1 | 0.3 | 0.6 | 0.9 | 1.2 | 1.4 | 1.5 |
| 1987 | 1.6 | 1.5 | 1.3 | 1.0 | 0.9 | 1.1 | 1.3 | 1.6 | 1.5 | 1.3 | 1.0 | 0.9 |
| 1988 | 0.7 | 0.3 | -0.2 | -0.7 | -1.4 | -1.7 | -1.6 | -1.3 | -1.4 | -1.6 | -1.9 | -1.9 |
| 1989 | -1.7 | -1.4 | -1.1 | -0.8 | -0.6 | -0.4 | -0.3 | -0.3 | -0.2 | -0.2 | -0.1 | 0.0 |
| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| 1990 | 0.2 | 0.3 | 0.3 | 0.3 | 0.2 | 0.2 | 0.3 | 0.4 | 0.4 | 0.4 | 0.4 | 0.5 |
| 1991 | 0.6 | 0.5 | 0.4 | 0.4 | 0.5 | 0.7 | 0.8 | 0.8 | 0.9 | 1.2 | 1.7 | 2.1 |
| 1992 | 2.3 | 2.2 | 2.0 | 1.7 | 1.4 | 0.9 | 0.5 | 0.3 | 0.2 | 0.1 | 0.1 | 0.3 |
| 1993 | 0.5 | 0.7 | 0.9 | 1.0 | 0.9 | 0.7 | 0.5 | 0.5 | 0.5 | 0.4 | 0.3 | 0.3 |
| 1994 | 0.3 | 0.3 | 0.4 | 0.5 | 0.6 | 0.6 | 0.7 | 0.8 | 1.0 | 1.1 | 1.3 | 1.4 |
| 1995 | 1.3 | 1.0 | 0.7 | 0.4 | 0.1 | -0.1 | -0.3 | -0.5 | -0.7 | -0.9 | -0.9 | -0.9 |
| 1996 | -0.9 | -0.8 | -0.6 | -0.4 | -0.3 | -0.3 | -0.2 | -0.2 | -0.2 | -0.3 | -0.3 | -0.3 |
| 1997 | -0.2 | -0.1 | 0.2 | 0.5 | 1.0 | 1.3 | 1.7 | 2.0 | 2.3 | 2.4 | 2.4 | 2.3 |
| 1998 | 2.2 | 1.8 | 1.3 | 0.8 | 0.1 | -0.5 | -1.2 | -1.4 | -1.5 | -1.5 | -1.6 | -1.6 |
| 1999 | -1.5 | -1.3 | -1.1 | -1.0 | -1.0 | -1.0 | -1.0 | -1.0 | -1.0 | -1.1 | -1.4 | -1.6 |
| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| 2000 | -1.7 | -1.4 | -1.1 | -0.8 | -0.6 | -0.5 | -0.4 | -0.4 | -0.4 | -0.6 | -0.7 | -0.7 |
| 2001 | -0.6 | -0.5 | -0.5 | -0.5 | -0.3 | -0.1 | 0.0 | 0.0 | 0.0 | -0.2 | -0.2 | -0.3 |
| 2002 | -0.1 | 0.0 | 0.0 | 0.1 | 0.4 | 0.7 | 0.9 | 1.1 | 1.3 | 1.4 | 1.5 | 1.2 |
| 2003 | 0.9 | 0.5 | 0.2 | -0.2 | -0.4 | -0.3 | 0.0 | 0.2 | 0.2 | 0.2 | 0.3 | 0.3 |
| 2004 | 0.3 | 0.1 | 0.1 | 0.2 | 0.3 | 0.5 | 0.7 | 0.8 | 0.9 | 0.8 | 0.7 | 0.7 |
| 2005 | 0.6 | 0.4 | 0.3 | 0.3 | 0.2 | 0.0 | -0.1 | -0.1 | 0.0 | -0.2 | -0.5 | -0.8 |
| 2006 | -0.9 | -0.9 | -0.6 | -0.4 | -0.1 | 0.0 | 0.1 | 0.3 | 0.5 | 0.8 | 0.9 | 0.9 |
| 2007 | 0.6 | 0.2 | -0.2 | -0.4 | -0.4 | -0.5 | -0.6 | -0.8 | -1.0 | -1.3 | -1.4 | -1.5 |
| 2008 | -1.6 | -1.5 | -1.3 | -0.9 | -0.8 | -0.5 | -0.3 | -0.2 | -0.3 | -0.4 | -0.6 | -0.8 |
| 2009 | -0.9 | -0.8 | -0.7 | -0.4 | -0.1 | 0.1 | 0.3 | 0.4 | 0.6 | 0.9 | 1.3 | 1.6 |
| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| 2010 | 1.5 | 1.1 | 0.6 | 0.1 | -0.5 | -1.0 | -1.3 | -1.5 | -1.7 | -1.7 | -1.7 | -1.6 |
| 2011 | -1.4 | -1.2 | -0.9 | -0.7 | -0.5 | -0.3 | -0.4 | -0.5 | -0.7 | -0.9 | -1.0 | -1.0 |
| 2012 | -0.8 | -0.6 | -0.6 | -0.5 | -0.3 | 0.0 | 0.3 | 0.4 | 0.4 | 0.2 | -0.1 | -0.4 |
| 2013 | -0.6 | -0.6 | -0.5 | -0.4 | -0.4 | -0.4 | -0.4 | -0.3 | -0.3 | -0.2 | -0.2 | -0.3 |
| 2014 | -0.5 | -0.5 | -0.3 | 0.0 | 0.1 | 0.0 | -0.1 | -0.1 | 0.1 | 0.4 | 0.5 | 0.6 |
| 2015 | 0.5 | 0.4 | 0.5 | 0.6 | 0.8 | 1.0 | 1.3 | 1.6 | 1.9 | 2.2 | 2.3 | 2.4 |
| 2016 | 2.2 | 1.8 | 1.3 | 0.5 | -0.1 | -0.6 | -0.9 | -1.0 | -1.1 | -1.1 | -1.1 | -1.0 |
| 2017 | -0.7 | -0.5 | -0.3 | -0.1 | 0.1 | 0.1 | -0.2 | -0.5 | -0.7 | -1.0 | -1.1 | -1.3 |
| 2018 | -1.1 | -1.0 | -0.9 | -0.7 | -0.3 | 0.0 | 0.1 | 0.2 | 0.4 | 0.7 | 0.8 | 0.7 |
| 2019 | 0.6 | 0.6 | 0.6 | 0.5 | 0.3 | 0.2 | 0.0 | -0.1 | 0.0 | 0.1 | 0.2 | 0.2 |
| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| 2020 | 0.1 | 0.1 | 0.0 | -0.3 | -0.6 | -0.8 | -0.8 | -0.9 | -1.2 | -1.5 | -1.5 | -1.4 |
| 2021 | -1.2 | -1.0 | -1.0 | -0.8 | -0.6 | -0.5 | -0.6 | -0.7 | -0.9 | -1.1 | -1.2 | -1.2 |
| 2022 | -1.2 | -1.2 | -1.3 | -1.3 | -1.2 | -1.0 | -0.9 | -1.0 | -1.1 | -1.1 | -1.0 | -1.0 |
| 2023 | -0.8 | -0.6 | -0.4 | -0.2 | 0.1 | 0.4 | 0.6 | 0.9 | 1.1 | 1.4 | 1.5 | 1.5 |
| 2024 | 1.2 | 0.9 | 0.5 | 0.1 | -0.3 | -0.5 | -0.5 | -0.6 | -0.8 | -0.8 | -0.9 | -1.1 |
| 2025 | -1.1 | -0.9 | -0.7 | -0.5 | -0.5 | -0.4 | -0.5 | -0.6 | -0.8 | -0.9 | -0.9 | -1.0 |
| 2026 | -0.9 | -0.7 |
Author’s Insight: Ashok Patel (2026): On the Dependence of RONI Rescaling on the Base Period
RONI is often described as being “climatology independent,” but this is only partly true. The index does successfully remove dependence on the mean tropical SST state by subtracting the tropical average anomaly from the Niño 3.4 anomaly, thereby minimizing the influence of background warming. However, the subsequent scaling step introduces a different kind of dependence. The monthly scaling factor (kₘ), derived from the ratio of standard deviations, is tied to the variance structure of the chosen base period. As a result, RONI is not fully independent of climatology; rather, it is independent of the mean state, but explicitly dependent on the variability framework imposed by the chosen rescaling base period.
Furthermore, the analysis shows that the scaling factor (k_m) is sensitive to the distribution and intensity of ENSO events within the base period. Changes in ENSO regime—such as periods dominated by La Niña or strong El Niño events—can alter the variance and hence the value of (k_m), leading to measurable differences in RONI. This demonstrates that RONI is a hybrid index: it combines a physically meaningful anomaly difference with a statistically derived normalization. Consequently, while RONI improves upon traditional indices by reducing mean-state bias, its magnitude remains influenced by the evolving variability of the climate system.
Relative Oceanic Niño Index (RONI) હવે El Niño અને La Niña ટ્રેક કરવા માટે NOAAનું સત્તાવાર ENSO સૂચક બન્યું
RONI (Relative Oceanic Niño Index) શું છે?
RONI એ ENSO (El Niño અને La Niña) માપવાનું એક સૂચક છે. તેમાં Niño 3.4 વિસ્તારનું તાપમાન લઈએ છીએ અને તેમાંમાંથી સમગ્ર ઉષ્ણકટિબંધીય (ટ્રોપિકલ) સમુદ્રનું સરેરાશ તાપમાન બાદ કરવા માં આવે છે.
આ રીતે, સમગ્ર વિશ્વના ગરમ થવાના અસરને ઘટાડીને માત્ર વિસ્તારનો તફાવત જોવા મળે છે.
આ મળેલ તફાવતને પછી થોડું “rescale” કરવામાં આવે છે જેથી તેની ફેરફાર (variance) Niño 3.4 જેટલી જ રહે.
- RONI +0.5°Cથી વધુ → El Niño
- RONI −0.5°Cથી ઓછું → La Niña
સારાંશ:
પ્રાથમિક RONI Nino3.4 અને ટ્રૉપિક્સ ના તાપમાનનો “ફરક” બતાવે છે અને તેને Nino3.4ના સમાન સ્તરે લાવવા માટે પ્રાથમિક RONIને rescale (એક ચોક્કસ ગુણાકાર) કરવા માં આવે છે, જેથી ENSO (El Niño અને La Niña) ને વધુ સારી Nino3.4 ની જેમ દર્શાવી શકાય.
ENSO સ્થિતિ: La Niña Advisory / El Niño Watch
હાલમાં La Niña ચાલુ છે.
પૂર્વ-મધ્ય પેસિફિક સમુદ્રમાં તાપમાન સામાન્ય કરતાં ઓછું છે અને વાતાવરણ પણ La Niña જેવી સ્થિતિ બતાવે છે.
આગામી 1 મહિનામાં La Niña ઘટીને ENSO-નોર્મલ સ્થિતિ થવાની શક્યતા છે, અને મે–જુલાઈ 2026 સુધી આ સ્થિતિ ચાલુ રહેવાની સંભાવના (~55%) છે.
જૂન–ઑગસ્ટ 2026 દરમિયાન El Niño વિકસવાની શક્યતા (~62%) છે અને તે 2026ના અંત સુધી ચાલુ રહી શકે છે.