ENSO Alert System Status: Final La Niña Advisory/El Niño Watch

Key Takeaways:

• CPC has issued a Final La Niña Advisory, indicating La Niña conditions have ended.
• The ENSO Alert System has shifted to El Niño Watch with possible development in 6 months.
• Pacific Ocean SST anomalies are warming, supporting a neutral to El Niño transition.
• Positive IOD and active MJO may influence India’s monsoon and cyclone activity.

El Niño impacts global weather patterns, and a lot of international agencies closely follow its development and progress. Climate Prediction Center is one such agency which monitors El Niño right from initial indications to its end and issues the various advisories. In its current bulletin, the CPC has changed the status of the ENSO Alert System. The CPC bulletin has issued Final La Nina Advisory. It means that La Nina conditions have ended. Also, the current status goes on to El Nino Watch. And it means conditions are favourable for development of El Nino with a notice period of 6 months.

Under the Tropical Ocean Global Atmosphere program (TOGA), a number of buoys or equipment is deployed between 7°N and 7°S latitudes in the Pacific Ocean. These buoys, placed in an array fashion, constantly record temperatures, which are further verified with satellite-derived temperatures. Ocean covers 71% of Earth’s surface, and scientists record sea surface temperatures (SSTs) to understand how the ocean communicates with Earth’s atmosphere. SSTs provide fundamental information on the global climate systems. SSTs are an essential parameter in atmospheric model simulation and weather prediction.

El Nino and La Nina are ocean-atmosphere coupled phenomena. SST data are especially useful for identifying the onset of El Nino and La Nina cycles. To measure SST, the scientists deploy temperature sensors on satellites, buoys, ships, ocean reference stations, and through marine telemetry. The NOAA-led U.S. Integrated Ocean Observing System (IOOS) and NOAA’s Center for Satellite Applications and Research (STAR) merge their data to provide SSTs worldwide.

ENSO: During El Nino, unusually warm sea surface temperatures in the central/eastern tropical Pacific lead to increased evaporation and resultant cooling of the ocean. Heat-generated evaporation increases the cloud cover, which in turn blocks the sunlight from entering the ocean. Also, when water vapour condenses and forms clouds, latent heat is released into the atmosphere. So, during El Nino, there is less heating of the ocean and more heating of atmosphere than normal. During La Nina, the opposite happens. With colder La Nina sea surface temperatures, there is less evaporative cooling of the ocean, less convective cloudiness blocking the Sun from heating the ocean, and less convective heating of the atmosphere.

During the last four weeks, below-average equatorial SSTs weakened in the east-central Pacific Ocean. Above-average SSTs persisted in the far-eastern equatorial Pacific Ocean. All the four Nino indices have warmed together, for the first time after 10 weeks. Nino 3.4 index, the marker for RONI, has turned positive after nearly eight months, since July 2025. The average value of Nino 3.4 index over the last four weeks was -0.17°C. This is supportive of cessation of La Nina and commencement of neutral conditions.

IOD: The Indian Ocean Dipole continues to hold very close to zero-zero mark. The IOD index value for the week ending 19 April 2026 was 0.01°C. April and May 2026 favour neutral IOD conditions, with a rising probability of positive IOD during the monsoon period.

MJO: The Madden-Julian Oscillation is likely to propagate eastward from Western Hemisphere and Africa to Indian Ocean in Phase 2. The amplitude is likely to reduce and the pulse may enter the inner circle. The continued eastward propagation of the MJO over the Indian Ocean and the Maritime Continent favours chances of development of tropical cyclone in early May over the Indian Seas.

The North American Multi-Model Ensemble (NMME) average, including the CFSv2, favours ENSO-neutral conditions through April-June 2026, with a transition to El Nino thereafter. El Nino is likely because of increasing sub-surface temperature anomalies and recent westerly wind anomalies over the western Pacific Ocean. The possible outcome continues to range from ENSO-neutral to very strong El Nino during the upcoming Northern Hemisphere winters.