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Subseasonal Weather Outlook and Review

Review of Regional Weather for February 2025

 

1. Overview

1.1 During February 2025, the Maritime Continent experienced a mix of below- to above-average rainfall, with generally below-average rainfall over parts of the central and southern regions, and above-average rainfall for the northeastern region (Figure 1). Over Mainland Southeast Asia, there were no notable anomalies, typical of the dry season for this region. The largest positive (wetter) anomalies were recorded over the central Philippines, while the largest negative (drier) anomalies were recorded over Java. There were disagreements between GSMaP-NRT and CMORPH-Blended datasets, with GSMaP-NRT showing stronger and more extensive dry anomalies as compared to CMORPH-Blended. More disagreements between the datasets are also evident across the Maritime Continent, including over the Malay Peninsula, Sumatra, southern Borneo, and Papua, with CMORPH-Blended tending to show drier conditions over these regions as compared to GSMaP-NRT.

1.2 The observed rainfall anomaly pattern of above-average rainfall over the northeastern Maritime Continent and below-average rainfall over the central and southern Maritime Continent isare consistent with the predictions from the subseasonal weather outlooks for February 2025 (3 – 16 February 2025, and 20 January – 2 February 2025). The observed pattern of above-average rainfall over northeastern Maritime is also consistent with the February 2025 seasonal outlook, although the below-normal rainfall over parts of the Maritime Continent is not well represented.

era5_rainfall_anomalies
cmorph_bld_rainfall_anomalies
Figure 1: Rainfall anomalies for February 2025 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 Below- to near-average temperatures were recorded over central and eastern Mainland Southeast Asia and parts of the western Maritime Continent in February 2025 (Figure 2). Elsewhere, above-average temperatures were recorded over western Mainland Southeast Asia and the central and eastern Maritime Continent. The coldest anomalies (-1°C – -2°C below average) were recorded over northern Viet Nam, while the warmest anomalies (1°C – 2°C above average) were recorded over central Myanmar.

era5_temperature_anomalies
Figure 2: Temperature anomalies for February 2025 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 In the first week of the February, a Madden-Julian Oscillation (MJO) signal was observed over the Maritime Continent (Phase 5). The MJO propagated eastwards through the Western Pacific (Phases 6 and 7) in the first two weeks of February, reaching the Western Hemisphere (Phase 8) at the start of the third week. The MJO signal weakened during the third week, becoming inactive shortly before emerging at the end of the month in the Western Hemisphere (Phase 1). For February, Phase 5 typically brings wetter conditions over much of the Maritime Continent and Phase 6 tends to bring wetter conditions over the eastern Maritime Continent. Phase 7 tends to bring drier conditions for the western Maritime Continent, and Phases 8 and 1 typically bring drier conditions to much of the Maritime Continent. This observed MJO signal is in line with the mix of below- to above-normal rainfall anomalies in Figure 1.

mjo_phase_diagram

 

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 In February 2025, La Niña conditions were present. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) indicated La Niña conditions and atmospheric indicators (cloudiness and trade winds) also showed signs of La Niña. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during this time of the year.