Global Climate Outlook: Weak La Niña Emerging, Warmer Conditions Ahead in SON 2025

The latest climate monitoring report shows that global sea-surface temperature (SST) anomalies remained broadly above average during May–July (MJJ) 2025, with especially strong warming in the extratropical latitudes. While much of the equatorial Pacific hovered near neutral, coupled ocean–atmosphere signals suggest the potential onset of a weak La Niña, which could influence rainfall and temperature patterns worldwide during the coming season.

Recent Oceanic Conditions: MJJ 2025

During the May–July period:

• Equatorial Pacific: SSTs near the Date Line were close to normal, and most Niño indices remained near average, with the exception of Niño 1+2, which showed slight warming. Despite near-neutral SSTs, rainfall anomalies and atmospheric coupling retained La Niña-like features.

• Indian Ocean Dipole (IOD): The IOD index stayed near neutral, showing no sustained positive or negative phase.

• Atlantic: SST anomalies in both the North Tropical Atlantic (NTA) and South Tropical Atlantic (STA) were close to normal, while above-average SSTs dominated the extratropical Atlantic.

Outlook for Oceanic Drivers: SON 2025

Looking ahead to September–November (SON) 2025, models project key oceanic shifts:

• Equatorial Pacific: Niño 3.4 and Niño 3 SST anomalies are forecast to decline, with the potential emergence of a weak La Niña. Strengthened warming in the western Pacific will likely intensify the east–west SST gradient, reinforcing La Niña-like conditions.

• Indian Ocean Dipole: The IOD index is projected to weaken and move into a negative phase, which typically enhances rainfall across parts of East Africa and Australia while reducing it over East Africa’s northern tier.

• Atlantic: Northern tropical Atlantic SSTs are forecast to remain above normal, while the southern tropical Atlantic stays near average.

Surface Temperature Outlook: SON 2025

A multi-model ensemble forecast indicates a strong global signal for above-normal surface temperatures, particularly across the Northern Hemisphere. Key regions include:

• Northern Hemisphere: Southern North America, western Europe, northwest Africa, northern Asia, eastern Asia, and the Arctic Circle all show elevated probabilities of warmer-than-normal conditions.

• Southern Hemisphere: New Zealand and western South America are projected to experience above-normal warmth, while Australia shows no clear temperature signal.

• Tropics: Equatorial Africa, Southeast Asia, and the Maritime Continent are forecast to experience persistent above-average temperatures, with strong model agreement.

• Oceans: Widespread warming is projected across the North Pacific, North Atlantic, and Indian Ocean basins, while cooler anomalies appear in the South Pacific near 120°W.

Rainfall Outlook: SON 2025

Rainfall predictions show a clear La Niña-like pattern, even though only a weak La Niña may develop:

• Pacific Basin:

  • Below-normal rainfall is expected from 150°E to the Date Line, extending eastward towards Central America and southeastward toward western South America near 35°S.

  • Along the equator, near-normal rainfall is projected from the Date Line to the South American coast.

• Enhanced Rainfall: Predicted over the Indian subcontinent, Southeast Asia, the Maritime Continent, the Philippines, eastern Australia, northern North America, and a band near 60°S in the southern Pacific.

• Suppressed Rainfall: Forecast for the equatorial Atlantic, southern Europe into central Asia, the Gulf of Guinea coast, the Greater Horn of Africa, and western parts of North America.

Broader Implications

The forecasted weak La Niña conditions, coupled with a negative IOD and persistent global warmth, suggest a season marked by regional climate extremes. While some areas may benefit from enhanced rainfall for agriculture, others risk drought stress, flooding, or heatwaves.

Scientists note that continued monitoring is crucial as even a weak La Niña can have outsized impacts on global weather, from influencing hurricane activity in the Atlantic to altering monsoon patterns in Asia.