Enso Status on 5th March 2025

Analysis & Commentary by Ashok Patel

Several international meteorological agencies including the Indian Meteorological Department and various private organization had anticipated the development of a La Niña event during the Indian Summer Monsoon of 2024. However, till end of February, just two La Niña thresholds have been achieved. Having a contrarian view, I had presented a counter perspective through monthly blog posts from July to February 2025. This March post is the latest take on this matter.

What is a Fully Developed La Niña?

To understand why the anticipated La Niña did not materialize, it’s important to define what constitutes a “fully developed La Niña,” or a “full-fledged La Niña,” based on NOAA’s operational definitions for ENSO (El Niño-Southern Oscillation):

• El Niño is characterized by a positive Oceanic Niño Index (ONI) greater than or equal to +0.5ºC.
• La Niña is defined by a negative ONI less than or equal to -0.5ºC.

For an event to be classified as a full-fledged El Niño or La Niña, the respective ONI threshold must be met or exceeded for at least five consecutive overlapping 3-monthly seasons.

ONI Data has been obtained from CPC – NWS – NOAA available here

The Niño3.4 SST has been recorded at -0.60°C for December 2024 and -0.74°C for January 2025 and -0.59°C for February 2025,. This gives the Oceanic Niño Index (ONI) of -0.6°C for (December-January-February) 2024-25 season, thereby attaining the Second La Nina threshold at the end of February 2025.

This development has potentially set the stage for a fully developed La Niña by May 2025, provided that La Niña thresholds are sustained across all overlapping three-month seasons until then. However, the presence of unusually warm Niño1.2 and Niño3 SST anomalies raises the possibility that the La Niña threshold may only be exceeded for four or fewer consecutive overlapping three-month seasons. If this happens, the developing La Niña could collapse, and historically, such an event would be classified as ENSO-neutral.

If La Niña fails to materialize, a reclassification of ENSO status cannot be ruled out due to potential adjustments in sea surface temperature (SST) norms for the Niño regions, based on the 1996–2025 base period. The CPC updates this 30-year base period every five years, with the next revision scheduled for early 2026.

How ONI is determined:

The ONI is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. Defined as the three-month running-mean SST departures in the Niño 3.4 region. Departures are based on a set of improved homogeneous historical SST analyses (Extended Reconstructed SST – ERSST.v5).

In real-time operations, the past 30-year base period (e.g. 1991–2020) will continue to be used to compute the departure from average. However, CPC will create an additional 30-year base period every 5 years (the next update will be at the beginning of 2026). When these 5 year updates occur, the ONI values over the most recent decade will change slightly because of the inclusion of more recent data. Every five years, this method takes care of climatological changes in the SST of Nino3.4 region and the buzz about the need to adopt Relative Nino Index is not justified.

NOAA Operational Definitions for El Niño and La Niña, El Niño: characterized by a positive ONI greater than or equal to +0.5ºC. La Niña: characterized by a negative ONI less than or equal to -0.5ºC. By historical standards, to be classified as a full-fledged El Niño or La Niña episode, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons.

CPC considers El Niño or La Niña conditions to occur when the monthly Niño3.4 OISST departures meet or exceed +/- 0.5ºC along with consistent atmospheric features. These anomalies must also be forecast to persist for 3 consecutive months.

The Climate Prediction Center (CPC) is a United States Federal Agency that is one of the NECP, which are a part of the NOAA

Latest Oceanic Nino Index Graph Shows Two La Nina Threshold
Achieved  At The End Of February 2025

 

 

 

 

The Table below shows the monthly SST of Nino3.4 Region and the Climate adjusted normal SST and SST anomaly from February 2023 to February 2025. Climate Base 1991-2020. ERSST.v5

Period    Nino3.4 ClimAdjust
YR   MON  Temp.ºC Temp.ºC ANOM ºC


2023   2   26.30   26.76   -0.46
2023   3   27.19   27.29   -0.11
2023   4   27.96   27.83    0.14
2023   5   28.40   27.94    0.46
2023   6   28.57   27.73    0.84
2023   7   28.31   27.29    1.02
2023   8   28.21   26.86    1.35
2023   9   28.32   26.72    1.60
2023  10   28.44   26.72    1.72
2023  11   28.72   26.70    2.02
2023  12   28.63   26.60    2.02
2024   1   28.37   26.55    1.82
2024   2   28.28   26.76    1.52
2024   3   28.42   27.29    1.12
2024   4   28.60   27.83    0.78
2024   5   28.17   27.94    0.24
2024   6   27.91   27.73    0.18
2024   6   27.90   27.73    0.17
2024   7   27.34   27.29    0.05
2024   8   26.74   26.86   -0.12
2024   9   26.46   26.72   -0.26
2024  10   26.45   26.72   -0.27
2024  11   26.46   26.70   -0.25
2024  12   26.00   26.60   -0.60
2025   1   25.81   26.55   -0.74
2025   2   26.17   26.76   -0.59

Indications and analysis of various International Weather/Climate agencies monitoring Enso conditions is depicted hereunder:

Summary by: Climate Prediction Center / NCEP  Dated 3rd February 2025

ENSO Alert System Status: La Niña Advisory

La Niña conditions are present.*
Equatorial sea surface temperatures (SSTs) are near-to-below average in the central and east-central Pacific Ocean. SSTs are above-average in the eastern Pacific Ocean.
La Niña conditions are expected to persist in the near-term, with a transition to ENSO-neutral likely during March-May 2025 (66% chance).

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.

Recent (preliminary) Southern Oscillation Index values as per The Long Paddock – Queensland Government.

The 30 Days average SOI for end of February 2025 was at 7.14, however, on 4th March 2025 it has decreased and is in the neutral zone at +5.7 as per The Long Paddock – Queensland Government. The 90 Days average SOI has decrease to +5.79 on 4th March 2025. Currently, both 30 Days as well as the 90 Days average SOI is on a declining trend.

 

As per BOM – Australia 5th March 2025

• The El Niño–Southern Oscillation (ENSO) remains neutral despite a brief period from December to February when the tropical Pacific shifted towards a La Niña-like state. SSTs in the central tropical Pacific have risen over the past 4 weeks, with the most recent value of Niño3.4 (−0.30 °C for the week ending 2 March) firmly within the neutral range.
• The Bureau’s model predicts neutral ENSO (neither El Niño nor La Niña) until at least July. This is consistent with all surveyed international models.
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