Rainfall
Seasonal Rainfall Outlook: June-August 2025 (JJA)
Issued: 23 May 2025
For JJA 2025, above-normal rainfall is predicted for much of the southern ASEAN region.
For JJA 2025, above-normal rainfall is predicted for much of the southern ASEAN region, based on the multi-model ensemble (Figure 1). The highest probability of above-normal rainfall is over the southeastern portion (more than 60% chance), with 40 – 60% chance for the rest of the region apart from the northwestern portion where there is no dominant tercile. Some (4-5) or most (6 or more) models agree on above-normal rainfall as the most likely tercile for the southern ASEAN region, apart from the northwestern portion. Model skill for predicting above-normal rainfall is moderate to good for the Maritime Continent.
For the northern ASEAN Region, there is little to no agreement on the dominant tercile over most parts of the region (less than four models in agreement, Figure 2). The exception is over the Philippines where there is some model agreement (4 – 5 models) on above-normal as the most likely tercile. Model skill is low to moderate for the northern ASEAN region.
Figure 1: Rainfall tercile summary predictions of the multi model ensemble for JJA 2025 (contains modified Copernicus C3S information).
Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for JJA 2025. Where there no dominant tercile, it refers to the number of models with near-normal tercile (contains modified Copernicus C3S information).
Figure 5: Average climatological rainfall's lower tercile boundary for JJA based on CHIRPS (Reference period: 1991-2020).
Figure 6: Average climatological rainfall's upper tercile boundary for JJA 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.