La Niña Playing Hard Ball: Full-fledged La Niña Unlikely During Indian Winter 2024-25
Enso Status on 6th November 2024
Analysis & Commentary by Ashok Patel
Several international meteorological agencies, including the Indian Meteorological Department and various private meteorological organizations in India, had anticipated the development of a La Niña event during the Indian Summer Monsoon of 2024. However, we took a different stance and published monthly blog posts to provide a counter perspective, as summarized below:
The first post was on 5th July 2024 tittled El Nino Ends & First Enso Neutral Thresh Hold Established End Of June 2024 – Full Fledged La Nina As Per NOAA Criteria Not Expected During Indian South West Monsoon 2024
The second post was on 09-08-2024 tittled NOAA Criteria Suggest Full-Fledged La Niña Unlikely in 2024 – Even A Single La Niña Threshold Unlikely During the Indian Southwest Monsoon
The third post was on 06-09-2024 tittled Much-Awaited La Niña Unlikely in 2024; La Niña Threshold Not Expected During Indian Southwest Monsoon
The fourth post was on 23-10-2024 tittled La Niña Threshold Not Yet Reached: Full-fledged La Niña Unlikely During Indian Winter 2024-25
And now, we present the fifth update regarding La Niña Playing a Hard Ball.
What is a Fully Developed La Niña?
To understand why the anticipated La Niña failed to 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 exceeded for at least five consecutive overlapping 3-month periods (or seasons).
In the case of the 2024 Indian Summer Monsoon, despite extensive monitoring, a La Niña event never materialized. The required threshold for La Niña, a negative ONI of -0.5ºC or lower, was never reached.
ONI Data has been obtained from CPC – NWS – NOAA available here
The Oceanic Niño Index (ONI) has further decreased to -0.2°C for the ASO 2024 season, maintaining the ENSO Neutral threshold through the end of October 2024. This marks the establishment of the fifth consecutive ENSO-neutral condition. To transition into a La Niña state, the ONI would need to drop to at least -0.5°C during the SON 2024 season. Specifically, the combined Niño3.4 sea surface temperature (SST) for September, October, and November 2024 would need to total at least -1.36°C.
As of now, the Niño3.4 SST was recorded at -0.25°C for September 2024 and -0.28°C for October 2024. To achieve the necessary three-month total, the SST in November would need to drop to -0.83°C. If this happens, the first La Niña threshold would be met for the SON 2024 season. This could potentially set the stage for a fully developed La Niña by March 2025, provided the La Niña thresholds are sustained across all consecutive overlapping three-month periods until then.
However, if the SST does not reach -0.83°C in the Niño3.4 region by November 2024, ENSO neutral conditions would continue. In that case, the earliest a fully developed La Niña could form would be in April 2025, again assuming the thresholds are maintained through the necessary overlapping three-month periods.
Based on this analysis and NOAA criteria, it is expected that the Indian Winter of 2024-25 (December 2024- February 2025) will conclude without a fully developed La Niña. Even if the La Niña threshold is met in any month before February 2025, a fully developed La Niña would still be unlikely, as there would not be enough time to maintain the required five consecutive overlapping three-month seasons for classification. There could even be a possibility of the first La Nina thresh hold being attained and if these thresh holds exceed only for a total period of 4 or less consecutive overlapping 3-month seasons, historically this period will be considered as Enso Neutral.
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).
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 Enso Neutral
Conditions Prevail At The End Of October 2024
The Table below shows the monthly SST of Nino3.4 Region and the Climate adjusted normal SST and SST anomaly from February 2023. 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 7 27.34 27.29 0.05 2024 8 26.74 26.86 -0.11 2024 9 26.47 26.72 -0.25 2024 10 26.44 26.72 -0.28
Indications and analysis of various International Weather/Climate agencies monitoring Enso conditions is depicted hereunder:
Summary by: Climate Prediction Center / NCEP Dated 28th October 2024
ENSO Alert System Status: La Niña Watch
ENSO-neutral conditions are present.*
Equatorial sea surface temperatures (SSTs) are near-to-below-average in the central and eastern Pacific Ocean.
La Niña is favored to emerge in September-November (60% chance) and is expected to persist through January-March 2025.*
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.
30 Days average SOI was +4.31 at the end of October 2024 and was +4.38 on 4th November 2024 as per The Long Paddock – Queensland Government and 90 Days average SOI was +3.69 on 4th November 2024. These are in the neutral zone.
As per BOM – Australia 29th October 2024
- ENSO is currently neutral.
- The Bureau’s model suggests SSTs are likely to remain within the ENSO-neutral range (−0.8 °C to +0.8 °C) throughout the forecast period.
- Of the 6 other climate models surveyed, only one suggests SSTs in the tropical Pacific are likely to touch or exceed the La Niña threshold (below −0.8 °C) throughout November to February, with another one forecasting SSTs to exceed the La Niña threshold but for only December and January.
- Should a La Niña develop in the coming months, it is forecast to be relatively weak (in terms of the magnitude of the SST anomaly) and short-lived, with all models indicating neutral-ENSO by February 2025.
- In order for observed conditions to be classified as a La Niña event, the cool waters in the tropical Pacific, and corresponding atmospheric indicators, must be sustained for at least 2 to 3 months.
- ENSO forecast skill is high at this time of year for up to 4 months ahead.
