Rainfall

Seasonal Rainfall Outlook: October-December 2023 (OND)

Issued: 29 Sep 2023

For OND 2023, models predict an increased chance of below-normal rainfall for most of the Maritime Continent and above-normal rainfall over parts of Mainland Southeast Asia.

For OND 2023, below-normal rainfall is predicted for most of the Maritime Continent, based on the multi-model ensemble (Figure 4). The ECMWF model (Figure 2) shows the highest confidence for below-normal rainfall for regions south of the equator, while the NCEP and the UKMO (Figures 1 and 3) models show high confidence over relatively smaller parts in the Maritime Continent. However, all three models predict an increase in chance of above-normal rainfall over the northwestern Maritime Continent. Models’ skill is moderate to good skill for below-normal rainfall over the Maritime Continent, and low to moderate for above-normal rainfall over the northwestern Maritime Continent.

For Mainland Southeast Asia, there is a small increase in chance of above-normal rainfall over much of the region, apart from over the where no dominant tercile is predicted, based on the multi-model ensemble (Figure 4). The NCEP model (Figure 1) predicts above-normal rainfall over much of Myanmar, much of Thailand and northern parts of Lao PDR and Viet Nam, while the ECMWF and UKMO models (Figures 2 and 3) predict a mix of near- to above-normal rainfall over these regions. The models’ skill is generally low to moderate over Mainland Southeast Asia for all three tercile categories.

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Figure 1: Rainfall tercile summary predictions of NCEP model for OND 2023 (contains modified Copernicus C3S information).
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Figure 2: Rainfall tercile summary predictions of ECMWF model for OND 2023 (contains modified Copernicus C3S information).
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Figure 3: Rainfall tercile summary predictions of UK Met Office model for OND 2023 (contains modified Copernicus C3S information).
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Figure 4: Rainfall tercile summary predictions of the multi-model ensemble for OND 2023 (contains modified Copernicus C3S information).
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Figure 5: Average climatological rainfall's lower tercile boundary for OND based on CHIRPS (Reference period: 1991-2020).
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Figure 6: Average climatological rainfall's upper tercile boundary for OND 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.