Rainfall

For September 2021, based on the multi-model ensemble (Figure 4), there is an increase in chance of above-normal rainfall over much of the Maritime Continent, apart from northern Sumatra and the Malay Peninsula with below-normal rainfall and northern Philippines with no dominant terciles predicted. The ECMWF and UK Met Office models (Figures 2 and 3) have the highest likelihood of above-normal rainfall over central and southern parts of the Maritime Continent, while the NCEP model predicts the highest likelihood over southern Sumatra, Java and the Philippines with no dominant terciles over central Maritime Continent (Figure 1). The models’ skill is relatively high for much of the Maritime Continent, apart from northern Sumatra, the Malay Peninsula, and northern Philippines where the skill is only low to moderate.

For Mainland Southeast Asia, there is disagreement between NCEP model and the other two models, with NCEP model predicting below-normal rainfall over much of the region while ECMWF and UK Met Office models predicting a small increase in chance of above-normal rainfall or no dominant rainfall for much of the region. The models’ skill is low for Mainland Southeast Asia.