Rainfall
Seasonal Rainfall Outlook: June-August 2026 (JJA)
Issued: 29 May 2026
For JJA 2026, models predict below-normal rainfall for the southern ASEAN region, with a mix of below- and above-normal rainfall predicted over much of the northern ASEAN region.
For JJA 2026, an increased chance of below-normal rainfall is predicted for the southern ASEAN region, based on the multi-model ensemble (Figure 1). Most models (more than six models) are in agreement with below-normal as the dominant tercile for much of the region. Model skill is moderate to good over the eastern and central parts of the southern ASEAN region and low to moderate over the western part at this time of the year.
For the northern ASEAN region, a mix of below- and above-normal rainfall is predicted for much of the region, apart from the northwestern parts where no dominant tercile is predicted. Some models (4 – 6 models) are in agreement regarding an increase in chance of below- and above-normal rainfall. Model skill is low for both below- and above-normal rainfall, apart from over southern Mainland Southeast Asia, where skill is low to moderate.
Figure 1: Rainfall tercile summary predictions of the multi model ensemble for JJA 2026 (contains modified Copernicus C3S information).
Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for JJA 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 JJA based on CHIRPS (Reference period: 1991-2020).
Figure 4: 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.