Rainfall

For August 2023, below-normal rainfall is predicted over much of the southern ASEAN region, with highest likelihood over the southwestern Maritime Continent based on the multi-model ensemble (Figure 4). The UK Met Office model (Figure 3) shows the highest confidence for below-normal rainfall over the southwestern Maritime Continent. The UK Met Office model also predicts below-normal rainfall over a larger spatial area over much of the southern ASEAN region, followed by the NCEP model (Figure 1). The ECMWF model (Figure 2) predicts below-normal rainfall over southern Sumatra, with near-normal rainfall elsewhere in the southern ASEAN region. Models’ skill is moderate to good for predicting below-normal rainfall and low to moderate for predicting near-normal rainfall for the southern ASEAN region.

For the northern ASEAN region, either no dominant tercile or above-normal rainfall is predicted, based on the multi-model ensemble (Figure 4). Above-normal rainfall is predicted over southwestern and southeastern Mainland Southeast Asia and parts of the Philippines. Elsewhere over Mainland Southeast Asia, the three models show a mix of below- to above-normal rainfall (Figures 1-3), with some disagreement between the models. The models’ skill is low to moderate for southern Mainland Southeast Asia and the Philippines, and generally low for rest of the northern ASEAN region.