October Global Seasonal Climate Update

Observed Oceanic Drivers for the Previous Season

During June-July-August (JJA) 2025, global sea-surface temperature (SST) anomalies remained generally above average, with particularly strong warmth across the extratropical latitudes.¹ In the equatorial Pacific, SSTs near the Date Line were close to normal, and all Niño indices hovered near-average-except for Niño 1+2, which showed a slight positive anomaly. Despite these near-neutral SST anomalies, coupled ocean-atmosphere signals in the central and eastern Pacific retained features consistent with a weak La Niña, particularly evident in observed rainfall anomalies (Figure 3, top). The Indian Ocean Dipole (IOD) index remained near average for the season, though it trended toward negative values later in the season. SST anomalies in both the North Tropical Atlantic (NTA) and South Tropical Atlantic (STA) were also close to normal, while above-normal SSTs persisted across the extratropical Atlantic.

Outlook for Oceanic Drivers for the Next Season

For October-November-December (OND) 2025, SST anomalies in the Niño 3.4 and Niño 3 regions are forecast to decline, with the potential emergence of a weak La Niña. Continued above-average SSTs in the western Pacific are expected to sustain a strong east-west SST gradient, reinforcing La Niña-like conditions across the equatorial Pacific. The IOD index is projected to shift into a negative phase. In the equatorial Atlantic, SSTs in the northern tropical region are forecast to remain slightly above average, while the southern tropical Atlantic is expected to stay near average.

Surface Temperature Outlook for the Next Season

For OND 2025, the multi-model ensemble forecast indicates a strong global signal for enhanced probabilities of above-normal surface temperatures, with generally high model agreement across much of the Northern Hemisphere. Southern and northeastern regions of North America, western Europe, northwest Africa, northern Asia, eastern Asia, and the Arctic Circle all show elevated probabilities for above-normal conditions, supported by robust model consistency.

In the Southern Hemisphere, enhanced probabilities for above-normal temperatures are predicted over New Zealand and southern regions of South America; most of Australia shows a lack of consistent signal.

In the tropics, strong enhancement in the probability of above-normal temperatures is forecast across equatorial Africa, Southeast Asia, and the Maritime Continent. These regions also exhibit moderate to strong model agreement, reinforcing the likelihood of persistent warmth.

Over the oceans, widespread above-normal temperatures are projected across the North Pacific, western Atlantic, and eastern Indian Ocean, with strong model agreement.

Elsewhere, below-normal conditions are limited but appear in a coherent patch in the South Pacific near 60°S, 120°W. Over the equatorial Pacific east of the Date Line, probabilities for below-normal temperatures are enhanced, while the region from 120°W to the coastal waters of South America shows increased probabilities for near-normal conditions.

Rainfall Outlook for the Next Season

Rainfall outlook for OND 2025 aligns with an enhanced positive east-west sea-surface temperature gradient across the equatorial Pacific, resembling conditions typically observed during a moderate La Niña-even though SST forecasts suggest only a weak La Niña may emerge. Enhanced probabilities for below-normal rainfall are expected to extend eastward from 150°E to near the Date Line. To the north of the equator, this dry signal branches eastward toward the western coast of South America, and to the south of the equator, it extends south-eastward toward the western coastal regions of South America near 35°S. Along the equator, probabilities for near-normal rainfall are forecast from 160°W to the South American coast.

Overall, the OND 2025 rainfall outlook reflects a La Niña-influenced pattern, with suppressed rainfall over the central and eastern Pacific and enhanced rainfall over the western Pacific and adjacent land regions.

Beyond the Pacific basin, enhanced probabilities for below-normal rainfall are predicted over southern Europe extending into Central Asia, coastal areas near the Gulf of Guinea, the Greater Horn of Africa extending into western Indian Ocean, and southern parts of North America. Probabilities for above-normal rainfall are increased over the Indian subcontinent, northern Asia and the Arctic Circle, Southeast Asia, the Maritime Continent, regions around the Philippines, the eastern half of Australia, northern parts of North America, and a zonal band near 60°S in the southern Pacific Ocean.

Figure 1. Probabilistic forecasts of surface air temperature and precipitation for the season October-November-December 2025. The tercile category with the highest forecast probability is indicated by shaded areas. The most likely category for below-normal, above-normal, and near-normal is depicted in blue, red, and grey shadings respectively for temperature, and orange, green and grey shadings respectively for precipitation. White areas indicate equal chances for all categories in both cases. The baseline period is 1993-2009.

¹ https://www.cpc.ncep.noaa.gov/products/people/mchen/AttributionAnalysis… ;