Monthly Archives: December 2023

1.1 During November 2023, a mix of below- to above-average rainfall was recorded over Southeast Asia (Figure 1). Near- to above-average rainfall was recorded over much of Mainland Southeast Asia, and a mix of below- and above-average rainfall was recorded over much of the Maritime Continent. The largest positive (wetter) anomalies were recorded over central Philippines and eastern coast of the Malay Peninsula based on GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates. In contrast, the largest negative (drier) anomalies were recorded over southern Java and Papua (in both GSMaP-NRT and CMORPH-Blended).

1.2 The observed rainfall anomaly pattern of above-average rainfall over parts of Mainland Southeast Asia and the mix below- and above-average rainfall over the Maritime Continent are broadly consistent with the predictions from the subseasonal weather outlooks for November 2023 (30 October – 12 November 2023 and 13 – 26 November 2023).

Figure 1: Rainfall anomalies for November 2023 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2022. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Above-average temperatures were recorded over the Maritime continent and much of Mainland Southeast Asia (Figure 2). The warmest anomalies (more than 1°C above average) were recorded over southern Myanmar, southern Sumatra, Java, Sulawesi, and Papua.

 

Figure 2: Temperature anomalies for November 2023 based on ERA-5 reanalysis. The climatological reference period is 2001-2022. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 No active Madden-Julian Oscillation (MJO) was observed during the first week of November 2023, based on the RMM index (Figure 3). In the second week of November, an MJO signal emerged over the Western Pacific (Phase 6), propagated eastward and maintained its strength in Phase 7. The MJO signal continued propagating eastwards through the Western Hemisphere and Africa (Phases 8 and 1) in Week 3, before decaying over the Indian Ocean (Phase 2) in the last week of the November. Typically for November, Phase 6 tends to bring wetter conditions for eastern Maritime Continent while Phase 7 tends to bring drier conditions for the western Maritime Continent. Phases 8 and 1 typically bring drier conditions for much of Southeast Asia during this time of the year, while Phase 2 tend to bring wetter conditions to parts of the western Maritime continent and drier conditions to eastern parts.

 

Figure 3: The MJO phase diagram. The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator (denoted in the text with the first day of the month in blue and the last day of the month in red). The distance of the index from the centre of the diagram is related to the strength of the MJO. Values within the grey circle are considered weak or indiscernible (data from the Bureau of Meteorology, Australia).

 

2.2 El Niño conditions persisted over the equatorial Pacific during November 2023. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) continue to show El Niño conditions, with key atmospheric indicators (cloudiness and trade winds) also supporting these conditions. A positive Indian Ocean Dipole is also present. El Niño events tend to bring drier and warmer-than-average conditions to much of the Maritime Continent during September to November. Positive Indian Ocean Dipole events also tend to bring drier conditions to most of the southern half of the Maritime Continent during this period.