Rainfall
Seasonal Rainfall Outlook: September-November 2021 (SON)
Issued: 31 Aug 2021
For SON 2021, there is an increased chance of above-normal rainfall over much of Southeast Asia.
For SON 2021, all three models – NCEP, ECMWF and UK Met Office (Figures 1-3) predict an increased chance of above-normal rainfall for much of the Maritime Continent, with highest likelihood over central and southern parts of the Maritime Continent. No dominant and below-normal terciles are predicted for parts of Peninsular Malaysia and Sumatra, respectively, by the three models. The model skill for the above-normal tercile category is moderate to relatively high for much of the Maritime Continent, with higher skill where the probability of above-normal rainfall is highest in Figure 4.
For Mainland Southeast Asia, there is slight increase in chance of above-normal rainfall predicted by ECMWF and UKMO models for much of the region, while NCEP model is predicting above-normal rainfall for Cambodia and Viet Nam and below-normal rainfall for northern parts of Mainland Southeast Asia. However, the model skill for Mainland Southeast Asia is only low for this season.
Figure 1: Rainfall tercile summary predictions of NCEP model for SON 2021.
Figure 2: Rainfall tercile summary predictions of ECMWF model for SON 2021 (contains modified Copernicus C3S information).
Figure 5: Average climatological rainfall's lower tercile boundary for SON based on CHIRPS (Reference period: 1991-2020).
Figure 6: 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.