Global Seasonal Climate Update for December-January-February 2024-25

Sea-surface temperature anomalies in the Niño 3.4 and Niño 3 regions are predicted to decline during December- February 2024-25 and are predicted to reflect weak La Niña conditions. Farther west in the Niño 4 region, the seasurface temperature anomaly is also predicted to decline and become negative. The strength of the IOD index is predicted to be near-average. In the equatorial Atlantic, SSTs are predicted to be above-normal in both the northern (NTA) and the southern (STA) regions during the season with a prediction for larger positive anomalies for NTA.

Figure 1. Probabilistic forecasts of surface air temperature and precipitation for the season December-February 2024-25. 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.

Consistent with the anticipated continuation of widespread above-normal sea-surface temperatures in all oceans except for the near-equatorial eastern Pacific Ocean, there is prediction of above-normal temperatures over almost all land areas. A few exceptions to this widespread warmth include land areas in the vicinity of the Bering Sea and the Gulf of Alaska, and Baja California. Extensive areas of large increases in probabilities for above-normal temperatures include South America (and particularly north of 15^o S), the Caribbean, Central America, southern,
eastern, and extreme northeast parts of North America, northern Europe. between 15^o S – 10^o N over Africa, western coastal and northeast regions of the Indian subcontinent, northern parts of eastern Asia, the Maritime continent, and New Zealand. Regions with moderate to weaker increase in probabilities for above-normal temperatures include northwestern North America, Greenland, southern Europe and northern Africa, Central Asia, southeast Asia, and Australia. In coastal areas of southern South America and extending north along the west coast to just north of the equator and into the eastern Pacific, consistent with the predicted emergence of weak La Niña, below- or nearnormal temperatures are expected.

Predictions for rainfall for December-February 2024-25 are consistent with the enhanced positive east to west sea surface temperature gradient typically observed during La Niña. Enhanced probabilities for near- or below-normal rainfall are predicted over a narrow band along or just north and south of the equator extending eastward from 150^o E to the western coast of South America. Below the equator, there is a band of enhanced probabilities for belownormal rainfall starting from 150^o W and extending south-eastwards to reach the western coast of South America and crossing into the southern Atlantic. Enhanced probabilities for below-normal rainfall are also predicted over the northeast South America extending into the Atlantic, North America below 45^o N, the Arabian Peninsula extending eastward into Central Asia, and over the Greater Horn of Africa extending into the Indian Ocean to 90^o E. Enhanced probabilities for above-normal rainfall are anticipated over the region centred over the Maritime Continent extending to cover the entire Australia and extending further eastward into the western Pacific to 150^o W, southern regions of Central America and the Caribbean, Arctic circle north of 60o N, and regions below 60^oS in the Southern Hemisphere. Other regions of enhanced probabilities for above-normal rainfall include a band off the coast of eastern Asia extending north-eastward to the Bering Sea and the Gulf of Alaska.