Rainfall
Seasonal Rainfall Outlook: September-November 2025 (SON)
Issued: 2 Sep 2025
For SON 2025, models predict above-normal rainfall over much of the Maritime Continent and eastern Mainland Southeast Asia
For SON 2025, above-normal rainfall is predicted for much of the Maritime Continent, based on the multi-model ensemble (Figure 1). The highest probability of above-normal rainfall is over the southern Maritime Continent. Most models agree on above-normal rainfall as the most likely tercile for much of the southern and eastern parts of the region (more than six models, Figure 2). Below-normal rainfall is predicted over the northwestern Maritime Continent by most models. Model skill for predicting above-normal rainfall is good for the southern, central and southeastern Maritime Continent and low to moderate elsewhere. Model skill for predicting below-normal rainfall is moderate over the northwestern Maritime Continent.
For Mainland Southeast Asia, above-normal rainfall is predicted apart from over the northwestern region. Most models agree on above-normal rainfall over the eastern portion (more than 6 models) with only some models agreeing for the central portion (4 – 6 models). No dominant tercile is predicted for northwestern Mainland Southeast Asia. Model skill is moderate to good for southeastern Mainland Southeast Asia and low to moderate elsewhere in the region.
Figure 1: Rainfall tercile summary predictions of the multi model ensemble for SON 2025 (contains modified Copernicus C3S information).
Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for SON 2025. Where there is no dominant tercile, it refers to the number of models with near-normal tercile (contains modified Copernicus C3S information).
Figure 3: Average climatological rainfall's lower tercile boundary for SON based on CHIRPS (Reference period: 1991-2020).
Figure 4: Average climatological rainfall's upper tercile boundary for SON based on CHIRPS (Reference period: 1991-2020).
The qualitative outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.