La Niña Threshold Not Yet Reached: Full-fledged La Niña Unlikely During  Indian Winter 2024-25

Enso Status on 21st October 2024

Ashok Patel’s Analysis & Commentary :

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

The Oceanic Niño Index (ONI) has further decreased to -0.1°C for the JAS 2024 season, maintaining the ENSO Neutral threshold through the end of September 2024. This marks the establishment of the Fourth ENSO Neutral condition. To transition into a La Niña state, the ONI must drop to at least -0.5°C for the ASO 2024 season. This would require the combined Niño3.4 sea surface temperature (SST) for August, September, and October 2024 to total at least -1.36°C.

As of now, the Niño3.4 SST was recorded at -0.11°C for August 2024 and -0.28°C for September 2024. Therefore, for October, the SST would need to drop to -0.97°C to achieve the necessary three-month total. If the SST drops to -0.97°C in Nino3.4 region for October 2024, the First La Nina thresh hold can be achieved for October 2024. Consequently, the earliest a full-fledged La Niña could potentially develop would be in February 2025, provided the La Niña thresh holds are sustained for the following four consecutive overlapping three-month periods.

If the SST does not reach -0.97°C in the Niño3.4 region for October 2024, ENSO neutral conditions would persist. In that case, the earliest a fully developed La Niña could establish would be March 2025, contingent on meeting the First La Niña threshold in November 2024 and maintaining it for four subsequent overlapping three-month periods.

Based on this analysis and NOAA criteria, it is expected that the Indian Winter of 2024-25 (ending February 2025) will conclude without a fully developed La Niña, even if the threshold is eventually met, due to the insufficient time for the required five consecutive overlapping three-month seasons.

In conclusion, while the potential impacts of La Niña on Indian winters are is not fully known as yet and is a subject of research, specifically with respect to how it affects different parts of the Country.

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 further 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 September 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   26.44   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 10th 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 +0.36 at the end of September 2024 and was +1.33 on 20th October 2024 as per The Long Paddock – Queensland Government and 90 Days average SOI was +1.96 on 20th October 2024.

 

 

 

As per BOM – Australia 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 exceed the La Niña threshold (below −0.8 °C) throughout November to January, and one forecasting SSTs below the 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.
• The likelihood of a La Niña developing in the coming months has decreased compared to recent updates.
• ENSO forecast skill is high at this time of year for up to 4 months ahead.