Overview of Current Monsoon and ENSO Events

As India awaits the summer monsoon forecast for 2025, there is an underlying concern regarding whether the year will experience an El Niño or La Niña event. Although these events account for only 60% of deficit and surplus rainfall years, they significantly impact perceptions and expectations regarding monsoon outcomes.

Current Sea Surface Temperature (SST) Patterns

• Since early 2024, SST patterns in the tropical Pacific Ocean have shown unexpected changes.
• Cold SST anomalies initially appeared in the far eastern tropical Pacific, indicating a potential La Niña.
• However, these anomalies shifted westward, with warm SST anomalies appearing in the far east by early summer 2024.
• Unusual anomalies in wind patterns were also observed, with strong easterly anomalies in the central-western tropical Pacific and westerly anomalies in the far east.

El Niño and La Niña Patterns

• Typical La Niña events feature cold SST anomalies in the far eastern to central tropical Pacific.
• El Niño events can present in two "flavours" with warm SST anomalies in either the east or central Pacific.
• The current pattern of warm SST anomalies in the far east and cold SST anomalies in the central Pacific is unusual.

Implications for Climate Predictions

The transition from the El Niño state in winter 2023-2024 to the anticipated La Niña in summer 2024 was complicated by a natural climate variability mode in the southern Pacific. This mode impacts wind anomalies and can determine SST conditions in the tropical Pacific.

Forecast Uncertainties

• Forecasts for 2025 are mixed, with some predicting a La Niña by fall, while others suggest a normal or even an El Niño year.
• The 2023 monsoon was normal despite a strong El Niño, thanks to the Indian Ocean Dipole (IOD), which remains controversial regarding its influence on the monsoon.

Challenges and Future Directions

The relationship between ENSO and the monsoon has evolved, affecting mid-latitude temperature anomalies, the jet stream, and pre-monsoon cyclones. These changes have implications for monsoon onset and intensity.

Climate models continue to struggle with accurately predicting these complex interactions, leading to uncertainty for farmers and policymakers. The India Meteorological Department and climate scientists are working diligently to improve forecast reliability.