Monthly Archives: April 2024

1.1 During March 2024, a mix of below-average to above-average was recorded over the southern half of the Maritime Continent, and below-average rainfall over most of the northern half of the Maritime continent (Figure 1). For Mainland Southeast Asia, below- to near-average rainfall was recorded in March over the southern region, with some pockets of above-average rainfall over the eastern and central regions. The largest positive (wetter) anomalies were recorded over central Borneo 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 northeast Borneo and southern Philippines (in both GSMaP-NRT and CMORPH-Blended).

1.2 The observed rainfall anomaly pattern of above-average rainfall over parts of the southern half of the Maritime Continent coupled with below-average rainfall over the northern half of the Maritime Continent are broadly consistent with the predictions from the subseasonal weather outlooks for March 2024 (4 – 17 March 2024 and 18 – 31 March 2024).

Figure 1: Rainfall anomalies for March 2024 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2023. 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 most of Mainland Southeast Asia (Figure 2) in March 2024. The exceptions were over parts of Myanmar and Cambodia, where below-to near-average temperature was recorded. The warmest anomalies (more than 1°C above average) were recorded over much of Thailand, parts of Lao PDR, the Malay Peninsula, central Sumatra, Borneo and Sulawesi.

Figure 2: Temperature anomalies for March 2024 based on ERA-5 reanalysis. The climatological reference period is 2001-2023. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 The Madden-Julian Oscillation (MJO) was active for much of March 2024, based on the RMM index (Figure 3). In the first and second weeks of March, the MJO signal present over the Indian Ocean (Phase 3) propagated eastwards through the Maritime Continent (Phases 4 and 5), with an increase in strength over Phase 4 at the end of Week 1. The active MJO signal continued propagating eastwards through the Western Pacific (Phases 6 and 7) in the third week of the month, before moving to Western Hemisphere (Phases 8 and 1) and weakened in strength in the last week of March. For March, Phases 4 and 5 tend to bring wetter conditions for the southern Maritime Continent, while Phases 6, 7 and 8 tend to bring drier conditions for the Maritime Continent.

 

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 over the equatorial Pacific continued weakening during March 2024. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) show a weakening of El Niño conditions and key atmospheric indicators (cloudiness and trade winds) are consistent with weakening El Niño conditions. Weakening El Niño events tend to ease drier conditions but continue warmer-than-average conditions to much of the Maritime Continent during January – March.