Category Archives: Regional Weather Review for Year 2025

Regional Weather Review for Year 2025

September 15, 2025

Review of Regional Weather for August 2025

1. Overview

1.1 During August 2025, many parts of Southeast Asia experienced above-average rainfall (Figure 1). Most of the Maritime Continent recorded positive (wetter) anomalies in both datasets (GSMaP-NRT and CMORPH-Blended), although CMORH-Blended (Figure 1, right) recorded negative (drier) anomalies over much of the western Maritime Continent, and parts of Borneo, the southeastern Maritime Continent and northern Philippines. Over Mainland Southeast Asia, positive anomalies were recorded over the east , with a mix of below- to above-average rainfall elsewhere. The largest positive (wetter) anomalies over Southeast Asia were recorded over eastern Mainland Southeast Asia and the southeastern Maritime Continent.

1.2 The observed rainfall anomaly pattern of above-average rainfall over much of the Maritime Continent is consistent with the predictions from the subseasonal weather outlooks for August 2025 (4 – 17 Aug 2025 and 18 – 31 Aug 2025). The subseasonal weather outlooks also predicted a mix of below-and above-average rainfall over parts of Mainland Southeast Asia, in line with the observations. The observations are also somewhat consistent with the seasonal outlook for August 2025, which predicted an increase in chance of above-normal rainfall in the southern and eastern Maritime Continent.

Figure 1: Rainfall anomalies for August 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 Near- to above-average temperatures were recorded over Mainland Southeast Asia in August 2025, while below- to near-average temperatures were recorded over most of the Maritime Continent (Figure 2). The coldest anomalies (0.25°C – 1°C below average) were recorded over Borneo and the southeastern Maritime Continent, in line with the above-average rainfall anomalies. The warmest anomalies (0.5°C – 2°C above average) were recorded over parts of central Mainland Southeast Asia, Sumatra, and Java.

Figure 2: Temperature anomalies for August 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 start of August, a Madden-Julian Oscillation (MJO) signal was present in the Western Hemisphere (Phase 8) based on the RMM diagram (Figure 3). This signal propagated eastwards, reaching the Indian Ocean (Phases 2 and 3) by the second week of August. However, as the signal approached the Maritime Continent (Phase 4) in the last week of August, the signal rapidly weakened and became indiscernible. At this time of the year, Phases 8 and 1 tend to bring drier conditions to southern Mainland Southeast Asia and the Philippines, and to a lesser extent, Phases 2 and 3 can bring wetter conditions to the western Maritime Continent. However, these patterns are not visible in Figure 1, indicating other drivers 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 There were signs of a negative Indian Ocean Dipole (IOD) developing in August 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.

August 21, 2025

Review of Regional Weather for July 2025

1. Overview

1.1 During July 2025, Southeast Asia experienced a mixed of below- to above-average rainfall, with the northwestern and parts of the central Maritime Continent as well as southern Mainland Southeast Asia experiencing below- to near-average rainfall while western and northern Mainland Southeast Asia and northern Philippines experienced above-average rainfall (Figure 1). The largest positive (wetter) anomalies were recorded over northern Philippines. However, there were some disagreements between GSMaP-NRT and CPC Unified Gauge datasets, with CPC Unified Gauge recording more intense below-average rainfall over Borneo and southern Mainland Southeast Asia.

1.2 The observed rainfall anomaly pattern of below-average rainfall over the Maritime Continent and southern Mainland Southeast Asia is mostly consistent with the predictions from the subseasonal weather outlooks for July 2025 (7 – 20 July 2025 and 21 July – 3 August 2025). The subseasonal weather outlooks also predicted the above-average rainfall over parts of Mainland Southeast Asia. The observations are also somewhat consistent with the seasonal outlook for July 2025, although the extent of the predicted region for below-normal rainfall is much smaller than the observed rainfall.

Figure 1: Rainfall anomalies for July 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 and near-average temperatures were recorded over much of northern Mainland Southeast Asia in July 2025, while above-average temperatures were recorded over most of the Maritime Continent and southern Mainland Southeast Asia (Figure 2). The coldest anomalies (-1°C – -2°C below average) were recorded over central Myanmar while the warmest anomalies (2°C – 3°C above average) were recorded over central Sumatra.

Figure 2: Temperature anomalies for July 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 There was no discernible Madden-Julian Oscillation (MJO) signal at the start of July based on the RMM diagram (Figure 3). In the middle of Week 2, an MJO signal developed over the Maritime Continent (Phase 4) which then propagated eastwards to the Western Pacific (Phases 6 and 7) by the end of Week 3. The MJO signal continued to propagate through the Western Pacific before decaying at the end of the month. At this time of the year, Phases 4 and 5 tend to bring wetter conditions to parts of the Maritime Continent while Phase 7 tends to bring drier conditions.

2.2 ENSO-neutral conditions were present in July 2025.

July 30, 2025

Review of Regional Weather for June 2025

1. Overview

1.1 During June 2025, Southeast Asia experienced a mixed of below- to above-average rainfall, with parts of the western Maritime Continent experiencing below- to near-average rainfall and above-average rainfall over the southeastern Maritime Continent (Figure 1). The largest positive (wetter) anomalies were recorded over central Viet Nam. However, there were notable disagreements between GSMaP-NRT and CPC Unified Gauge datasets. CPC Unified Gauge recorded more regions with below-average rainfall, in particular over parts of southeastern Mainland Southeast Asia and the central Maritime Continent, where GSMaP-NRT recorded near- to above-average rainfall.

1.2 The observed rainfall anomaly pattern of below-average rainfall over parts of western Mainland Southeast Asia is mostly consistent with the predictions from the subseasonal weather outlooks for June 2025 (26 May – 8 June 2025, 9 – 22 June 2025, and 23 June – 6 July 2025). The subseasonal weather outlooks for the other regions were mixed throughout the June 2025 period and is also reflective in the mixed of below- to above-average rainfall recorded. The observations are also somewhat consistent with the seasonal outlook for June 2025, where below-normal rainfall was predicted for parts of the western Maritime Continent and above-normal rainfall for parts of the southern Maritime Continent.

Figure 1: Rainfall anomalies for June 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 and near-average temperatures were recorded over much of Mainland Southeast Asia in June 2025, while near-average and above-average temperatures were recorded over most of the Maritime Continent, except over the Philippines and Papua where below-average temperature were recorded (Figure 2). The coldest anomalies (-0.5°C – -1°C below average) were recorded over parts of Cambodia and Viet Nam while the warmest anomalies (1°C – 2°C above average) were recorded over central Sumatra.

Figure 2: Temperature anomalies for June 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 There was no discernible Madden-Julian Oscillation (MJO) signal for most of June based on the RMM diagram (Figure 3). At the start of the month, the MJO was inactive based on the RMM Index. An MJO signal developed over the Western Pacific in the end of Week 1, propagated eastwards through the Western Pacific (Phases 6 and 7) by the middle of Week 2. The MJO signal decayed over the Western Hemisphere (Phase 8) in Week 3 and remained inactive for the rest of the month. At this time of the year, Phases 7 and 8 tend to bring drier conditions to parts of the Maritime Continent while Phase 4 tends to bring wetter conditions to this region. However, with the MJO being only briefly active during May, the MJO had little effect on the overall recorded rainfall during the month.

2.2 ENSO-neutral conditions were present in June 2025.

June 13, 2025

Review of Regional Weather for May 2025

1. Overview

1.1 During May 2025, much of Southeast Asia experienced above-average rainfall, with parts of the Maritime Continent and southeast Mainland Southeast Asia experiencing below-average rainfall (Figure 1). The largest positive (wetter) anomalies were recorded over western Myanmar, northeastern Borneo, and parts of Papua, with both datasets recording large negative (drier) anomalies over western Borneo. However, there were notable disagreements between GSMaP-NRT and CMORPH-Blended datasets, with CMOPRH. For the northwestern Maritime Continent CMORPH-Blended recorded a mix of above- and below-average rainfall, while GSMaP-NRT recorded below-average rainfall. CMORH-Blended recorded below- to near-average rainfall for Cambodia and northern Lao PDR, while GSMaP-NRT recorded near- to above-average. CMORPH-Blended also has larger negative anomalies over parts of Papua compared to GSMaP-NRT.

1.2 The observed rainfall anomaly pattern of above-average rainfall over much of western Mainland Southeast Asia and the southern Maritime Continent and drier conditions over parts of the western and central equatorial region is mostly consistent with the predictions from the subseasonal weather outlooks for May 2025 (28 April – 11 May 2025, 12 – 25 May 2025, and 26 May – 8 June 2025). The observations are also somewhat consistent with the seasonal outlook for May, above-normal rainfall was predicted for much of the eastern Maritime Continent and near- to above-normal rainfall for parts of Mainland Southeast Asia

Figure 1: Rainfall anomalies for May 2025 based on GSMaP-NRT data (left) and CMORPH-Blended 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 and near-average temperatures were recorded over much of Mainland Southeast Asia in May 2025, while near-average and above-average temperatures were recorded over most of the Maritime Continent (Figure 2). The coldest anomalies (-1°C – -2°C below average) were recorded over parts of western and central Myanmar, associated with regions of above-average rainfall. The warmest anomalies (0.5°C – 1°C above average) were recorded over southern Sumatra.

Figure 2: Temperature anomalies for May 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 There was no discernible Madden-Julian Oscillation (MJO) signal for most of May based on the RMM diagram (Figure 3). At the start of the month, there were signs of an MJO signal over the Western Hemisphere (Phase 8) but it became inactive by the end of the first week. In the last week of the May, the signal briefly emerged in Phase 4 for two days before staying inactive until the end of the month. At this time of the year, Phase 8 tend to bring drier conditions to parts of the Maritime Continent while Phase 4 tends to bring wetter conditions to this region. However, with the MJO being only briefly active during May, the MJO had little effect on the overall recorded rainfall during the month.

2.2 ENSO-neutral conditions were present in May 2025.

May 16, 2025

Review of Regional Weather for April 2025

1. Overview

1.1 During April 2025, much of the western Maritime Continent and western Mainland Southeast Asia experienced above-average rainfall, while much of the southern and northeastern Maritime Continent experienced below-average rainfall (Figure 1). The largest positive (wetter) anomalies were recorded over the Malay Peninsula. Outside of the regions mentioned above, there was either disagreements between GSMaP-NRT and CMORPH-Blended datasets or no notable anomalies. For much of the central and eastern equatorial region CMORPH-Blended recorded below-average rainfall, while GSMaP-NRT recorded above-average rainfall. CMORH-Blended also recorded below-average rainfall for Cambodia, while GSMaP-NRT was near-average.

1.2 The observed rainfall anomaly pattern of above-average rainfall over much of western Mainland Southeast Asia and the western Maritime Continent and drier conditions over the northeastern Maritime continent is consistent with the predictions from the subseasonal weather outlooks for April 2025 (31 March – 13 April 2025, and 14 – 27 April 2025). The observed pattern is also partly consistent with the April 2025 seasonal outlook of above-normal rainfall over western Mainland Southeast Asia, although the northwestern Maritime Continent was predicted to have a higher chance of above-normal rainfall.

Figure 1: Rainfall anomalies for April 2025 based on GSMaP-NRT data (left) and CMORPH-Blended 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 and near-average temperatures were recorded over most of Southeast Asia in April 2025, apart from over northern Myanmar and the Philippines (Figure 2). The coldest anomalies (-1°C – -2°C below average) were recorded over parts of western and southern Myanmar, associated with regions of above-average rainfall. The warmest anomalies (1°C – 2°C above average) were recorded over northern Myanmar.

Figure 2: Temperature anomalies for April 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 There was no discernible Madden-Julian Oscillation (MJO) signal for most of April based on the RMM diagram (Figure 3). During the last week of April, there were signs of an MJO signal over the Western Pacific (Phases 6 and 7) and the Western Hemisphere (Phase 8). Phases 6 and 8 tend to bring drier conditions to parts of the Maritime Continent at this time of the year, although this is not noticeable in the April rainfall anomalies, particularly for GSMaP-NRT.

2.2 ENSO-neutral conditions were present in April 2025. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) indicated a return to ENSO-neutral. Key atmospheric indicators of La Niña (reduced cloudiness and stronger trade winds in the central Pacific) were present earlier in March, but have since shown signs of weakening, in line with a transition to ENSO-neutral conditions.

April 28, 2025

Review of Regional Weather for March 2025

1. Overview

1.1 During March 2025, much of the Maritime Continent experienced above-average rainfall, except parts of the Philippines, the Malay Peninsula and the eastern Maritime Continent which experienced below-average rainfall (Figure 1). For Mainland Southeast Asia, below-average rainfall was recorded over parts of northeastern and southern region, with near average elsewhere. The largest positive (wetter) anomalies were recorded around the eastern coast of Sumatra to the southern tip of Malay Peninsula, while the largest negative (drier) anomalies were recorded over the northwestern Maritime Continent. There were disagreements between GSMaP-NRT and CMORPH-Blended datasets on the extent and magnitude of the dry anomalies, in particular over northern Lao PDR, northern Vietnam, parts of southern Philippines, southern Sumatra, Java and southeast Borneo, and Papua, with CMORPH-Blended showing stronger and more extensive dry anomalies as compared to GSMaP-NRT.

1.2 The observed rainfall anomaly pattern of above-average rainfall over much of the Maritime Continent is consistent with the predictions from the subseasonal weather outlooks for March 2025 (3 – 16 March 2025, and 17 – 30 March 2025). The observed pattern of above-average rainfall over the Maritime Continent is also consistent with the March 2025 seasonal outlook, although the below-normal rainfall over parts of the Maritime Continent is not well represented.

Figure 1: Rainfall anomalies for March 2025 based on GSMaP-NRT data (left) and CMORPH-Blended 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 A mix of normal and below-average temperatures were recorded over eastern half of Mainland Southeast Asia whereas above-average temperatures were recorded over the western half of Mainland Southeast Asia in March 2025 (Figure 2). Elsewhere, above-average temperature were recorded over much of the Maritime Continent, except over the northwestern region with below- to near-average temperature. The coldest anomalies (-1°C – -2°C below average) were recorded over parts of central Vietnam and northeastern Thailand, while the warmest anomalies (1°C – 2°C above average) were recorded over western Myanmar.

Figure 2: Temperature anomalies for March 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 In the first week of March, an active Madden-Julian Oscillation (MJO) signal was observed over the Western Hemisphere (Phase 1). In the second week of the month, the signal propagated eastwards through the Indian Ocean (Phases 2 and 3) and continued its eastwards propagation over the Maritime Continent (Phase 4) in the third week. The signal weakened towards the end of third week of March over the Maritime Continent and became indiscernible in the last week of the month. During this time of the year, Phase 1 typically bring drier conditions to the Maritime Continent. Phase 2 and 3 tend to bring wetter conditions over the western Maritime Continent, while Phases 4 and 5 typically bring wetter conditions over much of the Maritime Continent. This observed MJO signal during March is in line with the above-normal rainfall anomalies in Figure 1.

2.2 In March 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.

March 11, 2025

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 17 February – 2 March 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.

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.

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.

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.

February 18, 2025

Review of Regional Weather for January 2025

1. Overview

1.1 During January 2025, much of the Maritime Continent experienced above-average rainfall, with only parts of southern Philippines and the Malay Peninsula experiencing below-average rainfall (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 southern tip of Malay Peninsula, eastern coast of Sumatra, and northwest Borneo, while the largest negative (drier) anomalies were recorded over southern Philippines. There were disagreements between GSMaP-NRT and CMORPH-Blended datasets on the extent and magnitude of the dry anomalies over southern Philippines, with GSMaP-NRT showing stronger and more extensive dry anomalies as compared to CMORPH-Blended. More disagreements between the datasets are also evident over Sumatra and western 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 much of the Maritime Continent is consistent with the predictions from the subseasonal weather outlooks for January 2025 (6 – 19 January 2025, and 20 January – 2 February 2025). The observed pattern is also consistent with the January 2025 seasonal outlook of above-normal rainfall over parts of the Maritime Continent.

Figure 1: Rainfall anomalies for January 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-average temperatures were recorded over much of Mainland Southeast Asia in January 2025 (Figure 2). Elsewhere, positive temperature anomalies were recorded over parts of Myanmar and the eastern and northeastern Maritime Continent. The coldest anomalies (-2°C – -3°C below average) were recorded over parts of northeastern Thailand and northern Cambodia, while the warmest anomalies (1°C – 2°C above average) were recorded over northwestern Myanmar.

Figure 2: Temperature anomalies for January 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 January, no active Madden-Julian Oscillation (MJO) signal was observed. During the second week of the month, an active MJO signal emerged, and was present over the Western Hemisphere (Phases 8 and 1). Then, the signal propagated eastwards through the Indian Ocean (Phases 2 and 3) in the third week of January and continued its eastwards propagation over the Maritime Continent (Phases 4 and 5) in the last week of the month. During this time of the year, Phases 8 and 1 typically bring drier conditions to the Maritime Continent. Phase 2 and 3 and tend to induce wetter conditions over the western Maritime Continent, while Phases 4 and 5 typically bring wetter conditions over much of the Maritime Continent. This observed MJO signal during January is in line with the above-normal rainfall anomalies in Figure 1.

2.2 In January 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.