Issued: 26 August 2026
First forecast week: 31 August – 6 September 2026
Second forecast week: 7 – 13 Septmeber 2026

The post Subseasonal Weather Outlook (31 August – 13 September 2026) appeared first on ASMC.

In recent days, the hotspot and smoke haze situation over the southern ASEAN region has deteriorated further under the prolonged dry conditions. Based on satellite surveillance, widespread moderate to dense smoke haze was observed to emanate from clusters of hotspots detected in Kalimantan, with moderate to dense transboundary haze observed to drift northwards from the hotspot clusters in West Kalimantan. Moderate to dense smoke haze was also observed across large parts of southern and central Sumatra. 287 and 190 hotspots were detected in Kalimantan, and 65 and 81 hotspots were detected in Sumatra, on 24 and 25 August 2026 respectively from the NOAA-20 satellite.

Dry conditions are forecast to persist over most of the southern ASEAN region. Coupled with El Niño conditions that are predicted to strengthen over the coming months, the hotspot and smoke haze situation could escalate further, thereby increasing the risk of severe transboundary haze occurrence in the southern ASEAN region.

The post Alert20260826 – Activation of Alert Level 3 for the Southern ASEAN Region appeared first on ASMC.

1. Overview

1.1 During July 2026, a mix of near- to above-average rainfall was recorded over the ASEAN region (Figure 1). Parts of western and eastern Mainland Southeast Asia recorded above-average rainfall while central parts of Mainland Southeast Asia recorded below-average rainfall based on the two datasets (GSMaP-NRT and CMORPH-Blended). Elsewhere, the northwestern Maritime Continent recorded mostly above-average rainfall, with most of the northwestern Maritime Continent and equatorial region recording below-average rainfall. The largest positive (wetter) anomalies were recorded over western Myanmar and southern Malay Peninsula, with the largest negative (drier) anomalies over Sulawesi and the Maluku Islands.

1.2 The observed rainfall anomaly pattern of above-average rainfall over western Mainland Southeast Asia and the below-average rainfall over the southern and eastern Maritime Continent are consistent with the predictions from the subseasonal weather outlooks for July 2026 (6 – 19 July 2026 and 20 July – 2 August 2026). The wet anomalies over western Mainland Southeast Asia and the dry anomalies over the eastern Maritime Continent are consistent with the seasonal outlook for July 2026.

Figure 1: Rainfall anomalies for July 2026 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 For Mainland Southeast Asia, below-average temperature was recorded over parts of northern region, with above-average temperature over the southeastern parts and near-average temperature elsewhere (Figure 2). For much of the Maritime Continent, above-average temperature was recorded. The warmest anomalies (1°C – 2°C above average) were recorded over southern Sumatra. The coolest anomalies (-0.25°C – -0.5°C below average) were recorded over parts of northern Lao PDR.

Figure 2: Temperature anomalies for June 2026 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 The Madden-Julian Oscillation (MJO) was active over the Western Pacific and Western Hemisphere during much of July 2026. In Week 1, an MJO signal was present in the Western Pacific (Phase 7). In Week 2, the MJO signal propagated eastwards to the Western Hemisphere (Phase 8), staying in the Western Hemisphere (Phases 8) in Week 3, before decaying in Week 4 and becoming inactive by the end of the month. Phases 7 and 8 tend to bring drier conditions to much of the ASEAN region. This is somewhat in line with the drier conditions over the eastern Maritime Continent in Figure 1.

 

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 The El Niño conditions are now present in July 2026, with the Indian Ocean Dipole (IOD) in the neutral state. El Niño conditions can bring drier conditions to the Maritime Continent at this time of the year.

The post Review of Regional Weather for July 2026 appeared first on ASMC.

Issued: 12 August 2026
First forecast week: 17 – 23 August 2026
Second forecast week: 24 – 30 August 2026

The post Subseasonal Weather Outlook (17 – 30 August 2026) appeared first on ASMC.

1.1 Southwest Monsoon conditions continued over the ASEAN region throughout July 2026. The prevailing winds across the southern ASEAN region blew mainly from the southeast to south, while winds over the northern ASEAN region blew mostly from the southwest to west (Figure 1).

1.2 Showers were observed over many parts of the ASEAN region during the review period, except over Java and the Lesser Sunda Islands, where persistent dry conditions were observed (Figure 1). The southern parts of Sumatra, and the southern and central parts of Borneo also experienced periods of dry weather. On 10 July 2026, the Alert Level 1 for the southern ASEAN region was activated, signalling the start of the dry season. Over the northern ASEAN region, relatively higher rainfall was recorded over the northern parts of Viet Nam and the Philippines due to Typhoon Maysak, Bavi and Noul.

1.3 The hotspot counts for July 2026 over the ASEAN region were generally comparable to previous years (Figure 2 and 3), except in Cambodia, where hotspot counts were slightly higher relative to the past four years (Figure 3).

1.4 Hotspot activities were more persistent in West Kalimantan and parts of the Lesser Sunda Islands towards the latter half of the review period (Figure 4), with more intense fires detected in West Kalimantan as well (Figure 5). Slight to moderate smoke plumes were observed mainly over Java, parts of Borneo, and the northern and southern parts of Sumatra, with transboundary smoke haze observed to drift from West Kalimantan into the western parts of Sarawak on a few days (Figures 6 – 10). Slight to moderate smoke plumes were also observed over the central parts of Cambodia and Viet Nam on a few days.

The post Review of Regional Haze Situation for July 2026 appeared first on ASMC.

In recent days, prevailing dry weather conditions over the southern ASEAN region have resulted in an escalation in hotspot and smoke haze activities. Based on satellite surveillance, moderate smoke haze was observed to emanate from clusters of hotspots detected in the western and southern parts of Kalimantan. A few smoke plumes were also observed from hotspots detected in the southern parts of Sumatra. 185 and 371 hotspots were detected in Kalimantan, and 26 and 11 hotspots were detected in Sumatra, on 1 and 2 August 2026 respectively from the NOAA-20 satellite.

The hotspot and smoke haze situation over the region is expected to deteriorate as dry weather is expected to persist across the southern ASEAN region, coupled with El Niño conditions that are predicted to continue strengthening over the coming months. This could increase the risk of transboundary haze over the region.

The post Alert20260803 – Activation of Alert Level 2 for the Southern ASEAN Region appeared first on ASMC.

Issued: 29 July 2026
First forecast week: 3 – 9 August 2026
Second forecast week: 10 – 16 August 2026

The post Subseasonal Weather Outlook (3 – 16 August 2026) appeared first on ASMC.

Issued: 16 July 2026
First forecast week: 20 – 26 July 2026
Second forecast week: 27 July – 2 August 2026

The post Subseasonal Weather Outlook (20 July – 2 August 2026) appeared first on ASMC.

1. Overview

1.1 During June 2026, a mix of near- to above-average rainfall was recorded over the ASEAN region (Figure 1). Parts of southwestern Mainland Southeast Asia recorded above-average rainfall while eastern parts of Mainland Southeast Asia recorded below-average rainfall based on the two datasets (GSMaP-NRT and CMORPH-Blended). The western Maritime Continent recorded mostly above-average rainfall, with most of the southern and eastern region recording below-average rainfall, with a mix of below- to above-average rainfall over the central Maritime Continent. The largest positive (wetter) anomalies were recorded over the southern Malay Peninsula and southern and northern Myanmar, with the largest negative (drier) anomalies over Sulawesi and the Maluku Islands.

1.2 The observed rainfall anomaly pattern of above-average rainfall over southwestern Mainland Southeast Asia and the below-average rainfall over the southern and eastern Maritime Continent are consistent with the predictions from the subseasonal weather outlooks for June 2026 (25 May – 7 June 2026, 8 – 21 June 2026 and 22 June – 5 July 2026). The wet anomalies over southwestern Mainland Southeast Asia and the dry anomalies over the southern and eastern Maritime Continent are consistent with the seasonal outlook for June 2026. However, the seasonal outlook predicted below-normal rainfall as the dominant tercile for the western Maritime Continent for June 2026.

Figure 1: Rainfall anomalies for June 2026 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 Above-average temperature was recorded over the eastern half of Mainland Southeast Asia, with near-average temperature elsewhere (Figure 2). Above-average temperature was recorded for much of the Maritime Continent. The warmest anomalies (1°C – 2°C above average) were recorded over parts of central Viet Nam. The coolest anomalies (-0.25°C – -0.5°C below average) were recorded over parts of central Myanmar and Papua.

Figure 2: Temperature anomalies for June 2026 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 The Madden-Julian Oscillation (MJO) was active over the Western Hemisphere during much of June 2026. In Week 1, an MJO signal propagated eastwards from the Western Pacific (Phase 7) to the Western Hemisphere (Phase 8). The MJO signal continued propagating eastwards in the western Hemisphere (Phases 8 and 1) in Week 2, before decaying in Week 3 and becoming inactive by the end of the third week of the month. An MJO signal then emerged over the Western Pacific (Phase 6) at the end of June. Phase 8 tends to bring drier conditions to much of the ASEAN region, with Phase 1 can increase rainfall over parts of the western and central equatorial region, while reducing the likelihood of rainfall over much of the rest of the ASEAN region. This is somewhat in drier conditions over the eastern Maritime Continent and wetter conditions in western Maritime Continent in Figure 1.

 

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 The El Niño conditions are now present in June 2026, with the Indian Ocean Dipole (IOD) in the neutral state. El Niño conditions can bring drier conditions to the Maritime Continent at this time of the year.

The post Review of Regional Weather for June 2026 appeared first on ASMC.

1.1 Southwest Monsoon conditions became fully established in early June 2026. The prevailing winds across the southern ASEAN region blew mainly from the southeast to south, while the prevailing winds over the northern ASEAN region blew mostly from the south to west (Figure 1).

1.2 Rainfall prevailed over most parts of the ASEAN region during the review period, except over the southern parts of Sumatra and Borneo, as well as Java and the Lesser Sunda Islands where drier conditions were observed (Figure 1).

1.3 Over the southern ASEAN region, the hotspot counts for June 2026 were generally lower than or comparable to previous years (Figure 2). Over the northern ASEAN region, the hotspot counts for June 2026 were generally comparable to previous years, except in Thailand and the Philippines, where hotspot counts were slightly higher compared to the past 5 years (Figure 3).

1.4 During the review period, few to isolated hotspots were detected in the ASEAN region, with more persistent and intense fires in the southern parts of Sumatra, West Kalimantan, Java and the Lesser Sunda Islands, as well as parts of Viet Nam (Figure 4). During periods of dry weather over the southern ASEAN region, slight to moderate smoke plumes were observed emitting from hotspots detected mainly in the northern and central parts of Sumatra, Java and parts of Borneo (Figures 6, 7, 8 and 9).

The post Review of Regional Haze Situation for June 2026 appeared first on ASMC.