Monthly Archives: December 2025

1.1 During November 2025, a mix of below- to above-average rainfall was recorded for Southeast Asia (Figure 1). For the Maritime Continent, most of the northeastern and northwestern regions recorded positive (wetter) anomalies in both datasets (GSMaP-NRT and CMORPH-Blended), with a mix of below- to above-average rainfall recorded over the equatorial region. Over Mainland Southeast Asia, above-average rainfall was recorded mainly over the central and eastern regions. Generally, CMORH-Blended (Figure 1, right) recorded more extensive negative (drier) anomalies over the equatorial region. The largest positive (wetter) anomalies were recorded over the northwestern Maritime Continent , with the largest negative (drier) anomalies over central Borneo.

1.2 The observed rainfall anomaly pattern of above-average rainfall over the Mainland Southeast Asia and below-average rainfall over the central Maritime Continent is consistent with the predictions from the subseasonal weather outlooks for November 2025 (27 October – 9 November 2025, 10– 23 November 2025, and 24 November – 7 December 2025).The observations are also somewhat consistent with the seasonal outlook for November 2025, which predicted an increase in chance of above-normal rainfall over most of Mainland Southeast Asia and the northeastern Maritime continent, with an increase in chance of below-normal rainfall over the central Maritime Continent.

Figure 1: Rainfall anomalies for November 2025 based on GSMaP-NRT data (left) and CPC Global Unified Gauge-based Analysis data (right). The climatological reference period is 2001-2024. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Below-average temperatures were recorded over most of Mainland Southeast Asia in November 2025, while near- to above-average temperatures were recorded over most of Maritime Continent (Figure 2). The warmest anomalies (1°C – 2°C above average) were recorded over east central Sumatra, while the coolest anomalies (0.5°C – 1°C below average) were recorded over central Mainland Southeast Asia.

Figure 2: Temperature anomalies for November 2025 based on ERA-5 reanalysis. The climatological reference period is 2001-2024. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 At the start of November, the Madden-Julian Oscillation (MJO) was present over the Maritime Continent (Phase 5) based on the RMM diagram (Figure 3). It stalled over the Western Pacific (Phase 6) during Week 2 and then weakening in Phase 6 during the third week. The MJO strengthened again in Phase 6 towards the end of Week 3 and resumed its eastward propagation, reaching phase 7 in Week 4. At this time of the year, Phases 1 and 2 tend to bring drier conditions to the eastern Maritime Continent, while Phases 4 and 5 tend to bring wetter conditions to much of the Maritime Continent. However, these patterns are not clear in Figure 1, indicating other drivers and weather systems likely had a stronger influence on the region’s rainfall.

 

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 A negative Indian Ocean Dipole (IOD) was present in November 2025. Negative IOD events tend to bring wetter conditions to parts of the region, particularly the southern Maritime Continent, in line with the positive rainfall anomalies in Figure 1. La Niña conditions were also present. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during this time of the year.