Rainfall
Monthly Rainfall Outlook: September 2025
Issued: 2 Sep 2025
For September 2025, above-normal rainfall is predicted over most of the Maritime Continent, apart from the northwestern and northeastern regions.
For September 2025, above-normal rainfall is predicted over most of the Maritime Continent based on the multi-model ensemble (Figure 1), with most models (more than six models, Figure 2) predicting above-normal rainfall as the dominant tercile for the southern region. Some models (4 – 6) predict below-normal rainfall over the northwestern Maritime Continent, while there is little to no model agreement over the northeastern Maritime Continent.
For Mainland Southeast Asia, above-normal rainfall is predicted over much of the central region by some models (4 – 6 models in agreement), with most models (more than six models) predicting above-normal rainfall over the northeastern part.
Model skill is good for predicting above-normal rainfall over the southern Maritime Continent, low to moderate for predicting above-normal rainfall elsewhere in Southeast Asia, and low to moderate for predicting below-normal rainfall over the western Maritime Continent.
Figure 1: Rainfall tercile summary predictions of the multi model ensemble for September 2025 (contains modified Copernicus C3S information).
Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for September 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 September based on CHIRPS (Reference period: 1991-2020).
Figure 4: Average climatological rainfall's upper tercile boundary for September 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.