CPC Declares La Nina Conditions: BoM Differs Opinion

The Climate Prediction Center (CPC), the forecasting wing of the National Oceanic Atmosphere Administration (NOAA) has finally announced the commencement of La Nina conditions. The ENSO Alert System for the agency has changed the status from La Nina ‘Watch’ to La Nina ‘Advisory’. La Nina watch indicates favourable conditions for the development of La Nina with a notice period of 6 months. La Nina advisory is issued when La Nina is observed and expected to continue. The final La Nina advisory is issued when the La Nina conditions have ended.

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CPC states that equatorial sea surface temperatures (SSTs) are below average in the central and east-central Pacific Ocean. The agency adds that La Nina conditions are present and are expected to persist through Feb-Apr 2025 (59% chance) and a transition to ENSO-Neutral is likely during Mar-May 2025(60% chance). However, there is a little disagreement with the Bureau of Meteorology (BoM), Australia on the evolution of the La Nina event. The Bureau considers that the ENSO in the tropical Pacific remains neutral. BoM opines that while many of the indicators have recently met the threshold for La Nina, they have not been sustained for the levels or duration sufficient to warrant La Nina status.

यह भी पढ़ें: उत्तर-पश्चिम भारत में बारिश के आसार, जानें किस दिन होगी शुरुआत

Notwithstanding, the difference of opinion CPC and BoM have different threshold markers for La Nina and El Nino. While CPC considers the temperature anomaly of -0.5°C or more for the initiation of La Nina, the Bureau has the threshold value at -0.8°C. Also, there is a variation between the latest Nino 3.4 index of BoM and CPC. As per BoM, the most recent value of the Nino 3.4 SST index in the central Pacific Ocean to 05th Jan 2025 was -0.83°C, which meets the La Nina threshold of -0.8°C. The CPC Nino 3.4 index as of 06thJan 2025 was -0.7°C and repeated the same on 13thJan 2025. This also meets the CPC La Nina threshold of -0.5°C.

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ENSO: The Nino 3.4 index, the marker for the Oceanic Nino Index (ONI) has breached or exceeded the threshold mark of -0.5°C, for the fourth successive week. The mean value of the index for the last 4 weeks is -0.82°C, much above the threshold mark. However, the index needs to have a quarterly average mark of -0.5°C or more, for the start of the La Nina event. The CPC ONI value for the last 12 weeks from 28th Oct 2024 to 13th Jan 2025 works out to be -0.47°C, a shade lower than the specified threshold of -0.5°C.

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For the continuation of La Nina conditions, it is essential that the Nino 3.4 value gets sustained or grows to establish the La Nina event. In the recent observation, both ocean and atmospheric indicators are now showing signs of stronger coupling, which is more consistent with the La Nina event.

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IOD: As per BoM, the Indian Ocean Dipole is neutral as on 12thJan 2025. The model indicates that the IOD will remain neutral throughout the forecast period to May 2025. It is aligned with the typical IOD behaviour at this time of the year.

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MJO: The Madden-Julian Oscillation will propagate eastward from Phase 1 to Phase 3 over the next 2 weeks, sailing across the Indian Ocean. MJO pulse has been maintaining a very active phase. Tied with the developing La Nina conditions and a negative Indian Ocean Dipole, the tropical convection will become stronger. The equatorial belt across the South Andaman Sea, South Bay of Bengal, Sri Lanka, Comorin and Maldives region will witness enhanced convective activity. The La Nina event is likely to be brief and weak, too. Historically, it is very late in the typical ENSO cycle for La Nina events to get established. The event will have to battle against the ‘spring barrier’ for sustenance. Under such circumstances, the event may go on record to be the shortest in history.