Monthly Archives: October 2026

October 29, 2026

Alert20261029 – Downgrade to Alert Level 2 for Southern ASEAN Region

Downgrade to Alert Level 2 for the Southern ASEAN Region

Shower activities over the southern ASEAN region have returned in recent days, which has contributed to a reduction in hotspot counts and some improvement of the smoke haze situation in the region. Nevertheless, elevated hotspots activity and transboundary haze may still be observed over some parts of the southern ASEAN region where drier conditions are expected.

A total of 1 and 0 hotspots were detected in Sumatra, and a total of 64 and 54 hotspots were detected in Kalimantan on 27 and 28 October 2026, respectively. The hotspot and haze situation in the southern ASEAN region is expected to improve further as more rainfall is forecast in the coming weeks.

Review of Regional Haze Situation for September 2026

1.1 Southwest monsoon conditions persisted over the ASEAN region in September 2026, except over the northern parts of Sumatra and Peninsular Malaysia where showers were observed. The prevailing low-level winds blew mainly from the southeast over areas south of the Equator and turned to blow from the southwest or west over areas north of the Equator (Figure 1).

1.2 The southern ASEAN region remained under its traditional dry season throughout September 2026. Dry conditions prevailed over many parts of the region, except for isolated showers over parts of northern Sumatra, Malaysia, and the northern parts of Kalimantan. Meanwhile, showers were prevalent over the northern ASEAN region, with relatively drier conditions over the northern parts of the Mekong sub-region. Heavy rains and strong winds brought by the storms affected several areas in the northern ASEAN region, particularly the northern and central parts of Thailand, where several floods were reported.

Figure 1: Average Daily Rainfall and Mean Winds for September 2026. (Source: JAXA GsMaP and GFS, respectively)

1.3 The hotspot counts for the ASEAN region in September 2026 were the higher than or comparable to those recorded in the same month during previous years. Notably, Sumatra, Kalimantan and Viet Nam each recorded their highest September hotspot counts in five years (Figures 2 and 3).

Figure 2: Hotspot counts for the southern ASEAN region for September (2022-2026) based on NOAA-20 satellite surveillance.

Figure 3: Hotspot counts for the northern ASEAN region for September (2022-2026) based on NOAA-20 satellite surveillance.

1.4 During the review period, persistent scattered to widespread hotspots were detected in most of Kalimantan and the central and southern parts of Sumatra while isolated hotspots were detected elsewhere in the southern ASEAN region (Figure 4). Moderate to dense transboundary smoke plumes were seen originating from hotspots in large part of Kalimantan, with plumes drifting into Malaysia, Singapore and the Philippines (Figures 6, 7 and 8). Moderate to dense smoke plumes were also observed emanating from hotspot clusters in southern Sumatra on multiple days. With the exception of isolated hotspots detected in parts of Viet Nam and Thailand, hotspot and smoke haze activity over the northern ASEAN region remained subdued under the prevailing wet weather (Figure 4).

Figure 4: Distribution of hotspots detected in September 2026 based on NOAA-20 satellite surveillance.

Figure 5: Maximum fire intensity in September 2026 based on NOAA-20 satellite surveillance.

Figure 6: Number of days with moderate to dense smoke haze observed in September 2026 based on satellite imagery, ground observations, and air quality reports.

Figure 7: Moderate to dense smoke haze was observed over Borneo drifting into the western parts of Philippines on 2 September 2026. (Source: NOAA-20 satellite surveillance)

Figure 8: Moderate smoke haze was observed in the over Borneo and Sumatra, drifting into the Singapore and parts of Peninsular Malaysia on 5 September 2026. (Source: Himawari-9 satellite surveillance)

October 25, 2026

Subseasonal Weather Outlook (26 October – 8 November 2026)

Issued: 21 October 2026
First forecast week: 26 October – 1 November 2026
Second forecast week: 1 November – 8 November 2026

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier than usual conditions are predicted over much of the southern and eastern Maritime Continent in the next fortnight (26 October – 8 November).

Warmer than usual conditions are predicted over most of the ASEAN region in the next fortnight (26 October – 8 November).

In the middle of October, a Madden-Julian Oscillation (MJO) signal was present over the Western Hemisphere and Africa (Phase 1) based on the RMM Index. There is considerable uncertainty in the MJO outlook during the forecast period. While most models predict an MJO-like signal to develop over the Indian Ocean (Phases 2 and 3) in Week 1 (26 October – 1 November), this is similar to the forecast by some models from two weeks ago that did not transpire.

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.

October 23, 2026

Review of Regional Weather for September 2026

1. Overview

1.1 During September 2026, the Maritime Continent recorded generally below-average rainfall, while Mainland Southeast Asia recorded a mix of below- and above-average rainfall (Figure 1). The largest positive (wettest) anomalies were recorded over southern Thailand and southern Myanmar (both in GSMaP-NRT and CMORPH-Blended datasets). The largest negative (drier) anomalies were recorded over southern Borneo and southern Papua. For Mainland Southeast Asia, the southern and central part recorded predominantly above-normal rainfall, with below-normal rainfall over northern parts. However, there were some differences between the datasets, particularly over the northern parts where GSMaP-NRT recorded drier conditions over most of the region, while CMORPH-Blended recorded drier conditions mostly over northern Viet Nam.

1.2 The observed rainfall anomaly pattern of above-average rainfall over parts of Mainland Southeast Asia and below-average rainfall over most of the Maritime Continent is consistent with the predictions from the subseasonal weather outlooks for September 2026 (31 August – 13 September 2026 and 14 – 27 September 2026). The observations are also partly consistent with the seasonal outlook for September 2026, which predicted below normal rainfall over most of the Maritime Continent, but did not predict wetter conditions for southern Mainland Southeast Asia.

Figure 1: Rainfall anomalies for September 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 Most of the southern ASEAN region experienced above-average temperature, while much of the northern ASEAN region experienced near-average temperature (Figure 2). The warmest anomalies (2°C – 3°C above average) occurred over parts of southeastern Borneo, Sulawesi and southern Sumatra. Small negative (cool) anomalies were only recorded in isolated areas in Mainland Southeast Asia.

Figure 2: Temperature anomalies for September 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) signal was present over the Western Pacific (Phase 7) in the beginning of September 2026 based on the RMM, this signal briefly propagated eastwards before becoming inactive by the end of the week. Another MJO signal emerged during the third week of September over the Western Hemisphere (Phase 8) and then propagated eastward to Phase 1, before stalling in the last week of the month without further coherent eastward propagation. Phases 7 and 8 typically bring drier conditions to most of the Maritime Continent and parts of Mainland Southeast Asia, while Phase 1 brings drier conditions to central Maritime Continent, Mainland Southeast Asia and the Philippines. This is in line with drier conditions over most of the Maritime Continent, although not the wetter conditions over parts of Mainland Southeast Asia. The ongoing El Niño also likely played a more dominant role.

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 were present in September 2026, with the Relative Nino3.4 index supporting the strength of the El Niño to be strong. El Niño conditions typically bring drier conditions to most of the Maritime Continent at this time of the year, in line with the drier conditions observed in Figure 1.

October 7, 2026

Subseasonal Weather Outlook (12 – 25 October 2026)

Issued: 7 October 2026
First forecast week: 12 – 18 October 2026
Second forecast week: 19 – 25 October 2026

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier than usual conditions are predicted over most of the southern ASEAN region in the next fortnight (12 – 25 October). Drier than usual conditions are also predicted for much of northern Mainland Southeast Asia in Week 1 (12 – 18 October).

Warmer than usual conditions are predicted over most of the ASEAN region in the next fortnight (12 – 25 October).

While an active signal was present over the Western Hemisphere (Phases 8 and 1) in the first week of October based on the RMM index, its westward propagation was not characteristic of the Madden-Julian Oscillation (MJO). Most models predict no significant MJO activity by the start of the forecast period. During the forecast period (12 – 25 October), some models predict an MJO to emerge over the Indian Ocean (Phases 2 and 3) in Week 1 (12 – 18 October), while others suggest no significant MJO activity.