Rainfall
Monthly Rainfall Outlook: May 2026
For May 2026, below- to near-normal rainfall is predicted over much of the ASEAN region, apart from over parts of the western and central equatorial region where near- to above-normal rainfall is predicted.
For May 2026, over the Maritime Continent, a mix of below-normal to near-to above-normal rainfall is predicted, based on the multi-model ensemble (Figure 1). The highest probability of below-normal rainfall is over the southern Maritime Continent, where most of the models (more than six models, Figure 2) predict below-normal rainfall as the dominant tercile. Below-to near-normal rainfall is predicted over the eastern Maritime Continent, with four to nine models agreeing on below-normal rainfall as the dominant tercile. Over the western and central equatorial region, near- to above-normal rainfall (with four to six models in agreement) or no dominant tercile is predicted. Model skill is moderate for above-normal rainfall over the equatorial region and for below-normal rainfall over the southern Maritime Continent, and moderate to good for the eastern Maritime Continent.
Figure 1: Rainfall tercile summary predictions of the multi model ensemble for May 2026 (contains modified Copernicus C3S information).
Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for April 2026. 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 May based on CHIRPS (Reference period: 1991-2020).
Figure 4: Average climatological rainfall's upper tercile boundary for May 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.