Rainfall
Seasonal Rainfall Outlook: July-September 2021 (JAS)
Issued: 30 Jun 2021
For JAS 2021, there is an increased chance of above-normal rainfall for most of the equatorial ASEAN region from 8°N to 10°S.
For JAS 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 region over the equatorial ASEAN region from 8°N to 10°S (except for northern Sumatra and parts of Peninsular Malaysia where there is disagreement between the models). The model skill for the above-normal tercile category is moderate to relatively high for most of the equatorial region from 8°N to 10°S, apart from northern Sumatra and parts of Peninsular Malaysia where the model skill is low to moderate.
The three models also predict a small increase in chance of below-normal rainfall for the southern coastal parts of Mainland Southeast Asia. However, the model skill is low for these regions. Elsewhere, there is either no dominant terciles between the models or the model skill is low for this season.
Figure 1: Rainfall tercile summary predictions of NCEP model for JAS 2021.
Figure 2: Rainfall tercile summary predictions of ECMWF model for JAS 2021 (contains modified Copernicus C3S information).
Figure 5: Average climatological rainfall's lower tercile boundary for JAS based on CHIRPS (Reference period: 1991-2020).
Figure 6: Average climatological rainfall's upper tercile boundary for JAS 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.