NOAA Criteria Suggest Full-Fledged La Niña Unlikely in 2024 – Even A Single La Niña Threshold Unlikely During the Indian Southwest Monsoon

From Gujarart Weather

Ashok Patel

NOAA Criteria Suggest Full-Fledged La Niña Unlikely in 2024 – Even A Single La Niña Threshold Unlikely During the Indian Southwest Monsoon

Enso Status on 8th August 2024

Ashok Patel’s Analysis & Commentary :

ONI Data has been obtained from CPC – NWS – NOAA available here
The current data indicates that the Second ENSO Neutral thresh hold has been established at the end of July 2024, thereby Enso Neutral conditions continues. The ONI has dropped to +0.2°C for MJJ2024 season. Nino3.4 SST for June 2024 is 0.18°C and for July 2024 is 0.10°C and so for ONI of JJA2024, the combined total of three months Nino3.4 SST for June, July & August 2024 should at least go down to -1.36°C, so as to get ONI for JJA2024 as -0.5°C by rounding to one decimal.

Since Nino3.4 SST for June is 0.18°C and July is 0.10°C, it would mean that the Nino3.4 SST for August should theoretically go down to -1.64°C, so that the three months total reaches -1.36°C to make JJA2024 ONI -0.5°C to achieve La Nina thresh hold. Observing the Weekly Nino3.4 data, it is highly unlikely that Nino3.4 SST for August 2024 can go down to -1.64°C. Hence, ENSO Neutral condition is expected to continue for JJA2024 season.

Concluding from the above analysis, Enso Neutral conditions will prevail for JJA2024 and at the end of August, since only four months will be left in the current year 2024 full-fledged La Nina cannot be established, even if La Nina thresh hold is achieved in any of the four months remaining.

First conclusion is that La Nina thresh hold will not be achieved during the Indian Southwest Monsoon and Second conclusion is that a Full Fledged La Nina will not materialize during 2024, using the NOAA criteria.

The second conclusion as discussed is that since a La Nina thresh hold for JJA 2024 is not going to be achieved, the earliest La Nina thresh hold if at all it can be achieved is JAS2024, which is when the Indian Summer Monsoon ends.

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 July 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   27.39    27.29     0.10

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

Summary by: Climate Prediction Center / NCEP  Dated 8th August 2024

ENSO Alert System Status: La Niña Watch

Synopsis: ENSO-neutral is expected to continue for the next several months, with La Niña favored to emerge during September-November (66% chance) and persist through the Northern Hemisphere winter 2024-25 (74% chance during November-January).
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 -5.83 at the end of July 2024 and was -8.85 on 6th August 2024 as per The Long Paddock – Queensland Government and 90 Days average SOI was -3.06 on 6th August 2024.

As per BOM – Australia 6th August 2024

ENSO is neutral; a possibility of La Niña development during spring (Southern Hemisphere)

The ENSO Outlook is currently at La Niña Watch, meaning there are some signs that a La Niña may form in the Pacific Ocean later in 2024. A La Niña Watch does not guarantee that a La Niña will develop. The La Niña Watch is based on climate model forecasts and current atmospheric and oceanic conditions in the Pacific. Atmospheric and oceanic indicators are currently within ENSO-neutral thresh holds. While ENSO is likely to remain neutral until at least early spring. From October, 3 of 7 climate models suggest the
possibility of SSTs cooling to the La Niña threshold (below −0.8 °C). The remaining models suggest a continuation of ENSO-neutral conditions throughout the forecast period.

Note: All Seasons mentioned by BOM are with respect to Southern Hemisphere.