Monthly Archives: June 2025

June 18, 2025

Subseasonal Weather Outlook (23 June – 6 July 2025)

Issued: 18 June 2025
First forecast week: 23 – 29 June 2025
Second forecast week: 30 June – 6 July 2025

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over much of the western and central Maritime Continent in Week 1 (23 – 29 June). Drier conditions are then predicted over southern Mainland Southeast Asia and the southern half of the Philippines in Week 2 (30 June – 6 July).

Warmer than usual temperatures are predicted over most of the Maritime Continent in Week 1 (23 – 29 June). These warmer temperatures are predicted to persist over most of the Maritime Continent as well as develop over southern Mainland Southeast Asia in Week 2 (30 June – 6 July).

There was no Madden-Julian Oscillation (MJO) signal in the middle of June. Models predict no significant MJO activity during the forecast period.

The outlook is assessed for the region in general, where conditions are relative to the average conditions for the corresponding time of year. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.

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.

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 ENSO-neutral conditions were present in May 2025.

June 12, 2025

Alert20250612 – Activation of Alert Level 1 for the Southern ASEAN Region

Start of Dry Season for the Southern ASEAN Region

Dry weather conditions have developed over many parts of the southern ASEAN region in recent days, with the establishment of the Southwest Monsoon over the region. Prevailing winds are blowing mainly from the southeast or southwest. There was a total of 18 and 5 hotspots detected in the southern ASEAN region, mainly in parts of Sumatra and Kalimantan on 10 June 2025 and 11 June 2025, respectively.

The hotspot and smoke haze situation over the region may worsen as drier conditions over the southern ASEAN region are expected to persist in the coming months.

June 9, 2025

Review of Regional Haze Situation for May 2025

1.1 Inter-monsoon conditions prevailed throughout the ASEAN region during May 2025, characterised by light winds that varied in direction across most parts of the region (Figure 1).

1.2 Wet weather dominated over most parts of the ASEAN region as the monsoon rainband continued to shift northwards from the Equator, with the northern ASEAN region experiencing increased amounts of rainfall compared to previous months. Due to the expected persistent shower activities over the Mekong sub-region, the Alert Level was downgraded from Alert Level 2 to 1 on 13 May 2025, and subsequently from Alert level 1 to 0 on 21 May 2025, signalling the end of the dry season for the sub-region. While showers persisted over most areas in the southern ASEAN region this month, drier conditions were observed over parts of Sumatra and Kalimantan for a few days (Figure 1).

Figure 1: Average Daily Rainfall and Mean Winds for May 2025. (Source: JAXA GsMaP and GFS, respectively)

1.3 The hotspot counts for the ASEAN region for May 2025 were comparable to those recorded in May of previous years (Figure 2 & 3).

Figure 2: Hotspot counts for the northern ASEAN region for May (2021-2025) based on NOAA-20 satellite surveillance.

Figure 3: Hotspot counts for the southern ASEAN region for May (2021-2025) based on NOAA-20 satellite surveillance.

1.4 Isolated to scattered hotspots were detected over most parts of the Mekong sub-region, especially over the northern parts of Lao PDR where intense and persistent hotspot clusters were observed (Figure 4 and 5). Moderate to dense transboundary smoke haze was also observed to drift eastwards from the northern parts of Lao PDR into the northern parts of Viet Nam on a few days (Figure 6 and 7).

1.5 1.5 Over the southern ASEAN region, the hotspot and smoke haze situation remained mostly subdued. However, there were a few days when slight localized smoke plumes were observed emanating from hotspots in the central parts of Sumatra, the western parts of Kalimantan and Sarawak (Figure 4, 5 and 8).

Figure 4: Distribution of hotspots detected in May 2025 based on NOAA-20 satellite surveillance.

Figure 5: Maximum fire intensity in May 2025 based on NOAA-20 satellite surveillance.

Figure 6: Number of days with moderate to dense smoke haze observed in May 2025 based on satellite imagery, ground observations, and air quality reports.

Figure 7: Moderate to dense transboundary smoke haze observed over the northern parts of Lao PDR and Viet Nam on 7 May 2025. (Source: NOAA-20 satellite surveillance)

Figure 8: Localised smoke plume observed to emit from hotspots detected in Sarawak on 6 May 2025. (Source: NOAA-20 satellite surveillance)

June 4, 2025

Subseasonal Weather Outlook (9 – 22 June 2025)

Issued: 4 June 2025
First forecast week: 9 – 15 June 2025
Second forecast week: 16 – 22 June 2025

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over parts of the northern ASEAN region in Week 1 (9 – 15 June), in particular over central and eastern Mainland Southeast Asia and the Philippines. Wetter conditions are also predicted over much of the southern ASEAN region in Week 2 (16 – 22 June).

Warmer than usual temperatures are predicted over most of the southern ASEAN region in Week 1 (9 – 15 June).

There were signs of a Madden-Julian Oscillation (MJO) signal developing over the eastern Maritime Continent (Phase 5) during the beginning of June. Most models predict the MJO signal to propagate eastwards to the Western Pacific (Phases 6 and 7) by the start of the forecast period before decaying by the end of the first week.