Rainfall
Monthly Rainfall Outlook: May 2021
Issued: 30 Apr 2021
For May 2021, there is a small increase in chance of below-normal rainfall for the western Maritime Continent and a small increase in chance of above-normal rainfall for much of the northern ASEAN region.
For May 2021, based on the multi-model ensemble there is an increased chance of above-normal rainfall over the Philippines and much of Mainland Southeast Asia (Figure 4). Based on the individual models: the UK Met Office model (Figure 3) predicts above-normal rainfall over most Mainland Southeast Asia and the Philippines, the ECMWF model (Figure 2) predicts above-normal rainfall for western and central parts of Mainland Southeast Asia and the Philippines, while the NCEP model (Figure 1) only predicts small parts of Mainland Southeast Asia to receive above-normal rainfall with the Philippines and Myanmar predicted to experience below-normal rainfall. The models’ skill is moderate to relatively good for the Philippines, with low to moderate skill for Mainland Southeast Asia.
All three models predict below-normal rainfall for much of the western Maritime Continent, although the model skill is only low to moderate for this region.
Elsewhere (Java region and eastern Indonesia), there is either disagreement between the models or no dominant tercile predicted.
Figure 1: Rainfall tercile summary predictions of NCEP model for May 2021.
Figure 2: Rainfall tercile summary predictions of ECMWF model for May 2021 (contains modified Copernicus C3S information).
Figure 3: Rainfall tercile summary predictions of UK Met Office model for May 2021 (contains modified Copernicus C3S information).
Figure 4: Rainfall tercile summary predictions of the multi-model ensemble for May 2021 (contains modified Copernicus C3S information).
Figure 5: Average climatological rainfall's lower tercile boundary for May based on CHIRPS (Reference period: 1981-2010).
Figure 6: Average climatological rainfall's upper tercile boundary for May based on CHIRPS (Reference period: 1981-2010).
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.