For SON 2026, a high probability of below-normal rainfall is predicted over most of the Maritime Continent based on the multi-model ensemble (Figure 1). The exceptions are over the northwestern Maritime Continent, where above-normal rainfall is predicted, and parts of Borneo, where there is less agreement between the models (four to six models in agreement that below-normal rainfall is the most likely tercile). Otherwise, most models agree that below-normal rainfall is the most likely tercile for SON (Figure 2). Model skill for below-normal rainfall is good over the Maritime Continent where a high probability of below-normal rainfall is predicted, and low to moderate elsewhere. Model skill for above-normal rainfall over the northwestern Maritime Continent is low to moderatel.

For much of Mainland Southeast Asia, there is little agreement between the models (Figure 2). The main exceptions are over parts of eastern and coastal western Mainland Southeast Asia, where much of the models (four to six) predict below-normal rainfall as the most likely tercile, and parts of northern Mainland Southeast Asia, where much to most (four or more) models predict above-normal rainfall as the most likely tercile. Model skill is low for above-normal rainfall over northern Mainland Southeast Asia. For below-normal rainfall, model skill is moderate to good over southern and eastern Mainland Southeast Asia, and low elsewhere.

Rainfall

Rainfall

Seasonal Rainfall Outlook: September-November 2026 (SON)