Rainfall
Monthly Rainfall Outlook: September 2023
Issued: 31 Aug 2023
For September 2023, below-normal rainfall is predicted over most of the southern ASEAN region.
For September 2023, below-normal rainfall is predicted over most of the southern ASEAN region, with highest likelihood over the southwestern Maritime Continent based on the multi-model ensemble (Figure 4). The ECWMF model (Figure 2) shows the highest confidence for below-normal rainfall, followed by the NCEP and the UKMO models (Figures 1 and 3). Models’ skill is moderate to good skill for below-normal rainfall over the southern ASEAN region.
For the northern ASEAN region, there is an increased chance of above-normal rainfall over western and southern parts of the region, based on the multi-model ensemble (Figure 4). Above-normal rainfall is predicted over western and southern parts Mainland Southeast Asia and parts of the Philippines in all three models (Figures 1-3). Elsewhere over Mainland Southeast Asia, either there is no dominant tercile or disagreement between the models (central and eastern parts of Mainland Southeast Asia). Models’ skill is low to moderate for southern Mainland Southeast Asia and the Philippines, and generally low for rest of the northern ASEAN region.
Figure 1: Rainfall tercile summary predictions of NCEP model for September 2023 (contains modified Copernicus C3S information).
Figure 2: Rainfall tercile summary predictions of ECMWF model for September 2023 (contains modified Copernicus C3S information).
Figure 3: Rainfall tercile summary predictions of UK Met Office model for September 2023 (contains modified Copernicus C3S information).
Figure 4: Rainfall tercile summary predictions of the multi-model ensemble for September 2023 (contains modified Copernicus C3S information).
Figure 5: Average climatological rainfall's lower tercile boundary for September based on CHIRPS (Reference period: 1991-2020).
Figure 6: Average climatological rainfall's upper tercile boundary for September 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.