Monthly Archives: November 2025

November 26, 2025

Review of Regional Weather for October 2025

1. Overview

1.1 During October 2025, a mix of below- to above-average rainfall was recorded for Southeast Asia (Figure 1). For the Maritime Continent, most of the southern and eastern regions recorded positive (wetter) anomalies in both datasets (GSMaP-NRT and CMORPH-Blended), with below-average rainfall recorded over the western region and parts of the Philippines. Over Mainland Southeast Asia, below-average rainfall was recorded over the southern region, with near- to above-average rainfall elsewhere. Generally, CMORH-Blended (Figure 1, right) recorded more extensive negative (drier) anomalies over the western Maritime Continent and southern Mainland Southeast Asia. The largest positive (wetter) anomalies were recorded over eastern Mainland Southeast Asia, with the largest negative (drier) anomalies over the western Maritime Continent.

1.2 The observed rainfall anomaly pattern of above-average rainfall over the southern and southeastern Maritime Continent is consistent with the predictions from the subseasonal weather outlooks for October 2025 (1 – 12 Oct 2025 and 13 – 26 Oct 2025). However, the below-average rainfall observed was not predicted in the subseasonal weather outlook. The observations are also somewhat consistent with the seasonal outlook for October 2025, which predicted an increase in chance of above-normal rainfall in the southern and eastern Maritime Continent, and an increase in chance of below-normal rainfall in the western Maritime Continent.

Figure 1: Rainfall anomalies for October 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 most of Southeast Asia in October 2025, with the exception of below-average temperatures recorded over Papua (Figure 2). The warmest anomalies (1°C – 2°C above average) were recorded over northern Myanmar, while the coolest anomalies (0.5°C – 1°C below average) were recorded over northern Papua.

Figure 2: Temperature anomalies for October 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 the start of October, the Madden-Julian Oscillation (MJO) decayed over the Indian Ocean (Phase 2) and remained inactive in Week 1 and start of Week 2 based on the RMM diagram (Figure 3). An MJO signal then emerged over the Western Hemisphere (Phase 1) towards the end of Week 2, propagating eastwards to the Indian Ocean (Phases 2 and 3) in Week 3 and to the Maritime Continent (Phases 4 and 5) in Week 4. At this time of the year, Phases 1 and 2 tend to bring drier conditions to the eastern Maritime Continent, while Phases 4 and 5 tend to bring wetter conditions to much of the Maritime Continent. However, these patterns are not clear in Figure 1, indicating other drivers and weather systems 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 A negative Indian Ocean Dipole (IOD) was present in October 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. La Niña conditions were also present. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during this time of the year.

November 19, 2025

Subseasonal Weather Outlook (24 November – 7 December 2025)

Subseasonal Weather Outlook (24 November – 7 December)

Issued: 19 November 2025
First forecast week: 24 – 30 November 2025
Second forecast week: 1 – 7 December 2025

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over much of Mainland Southeast Asia in Week 1 (24 – 30 November). Drier conditions are also predicted over the southern Maritime Continent in Week 2 (1 – 7 December).

Wetter conditions are predicted over parts of the western Maritime Continent in Week 1 (24 – 30 November).

Cooler than usual temperatures are predicted over much of Mainland Southeast Asia in Week 1 (24 – 30 November).

A Madden-Julian Oscillation (MJO) signal was present in the Western Pacific (Phase 6) during the middle of November, based on the RMM index. Most models predict an MJO signal to propagate from Phase 6 to Phase 7 during the forecast period (24 November – 7 December).

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.

November 14, 2025

ASMC Bulletin (Issue #13, 2025)

November 12, 2025

25th ASEAN COF (October 2025)

Twenty Fifth Session of the ASEAN Climate Outlook Forum (ASEANCOF-25)

27 – 30 October 2025, Online

Consensus Bulletin for December-January-February (DJF) 2025/2026 Season

The ASEAN Climate Outlook Forum (ASEANCOF) is an avenue to collaboratively develop consensus-based seasonal climate outlooks and related information on a regional scale. The forum’s outlook and its activities contribute significantly to one of the key roles of the ASEAN Specialised Meteorological Centre (ASMC), which is to conduct climate and seasonal prediction for the Association of Southeast Asian Nations (ASEAN) region through pooling the expertise of ASEAN National Meteorological and Hydrological Services (NMHSs). In 2021, the ASEANCOF Working Group was established with the goal to guide and support the long-term development of ASEANCOF, in particular regarding the implementation of objective outlooks.

The Twenty-fifth session of ASEANCOF (ASEANCOF-25) was organised by the Ministry of Water Resources and Meteorology, Cambodia (MOWRAM), RIMES, ASMC, the ASEANCOF Working Group, UN ESCAP, and WMO. Participants from the NMHSs of ASEAN Member States created a consensus forecast for the boreal winter monsoon 2025/2026 in the ASEAN region. The consensus for the December-January-February (DJF) 2025/2026 outlook was achieved through an online session, which included presentations from different NMHSs, questionnaires, and discussions regarding the current climate conditions and predictions for Southeast Asia. The theme of ASEANCOF-25 was on advancing the tailoring of climate services to better meet the diverse needs of users across the ASEAN region. On the last day of ASEANCOF-25, a sharing session was held which included a panel discussion on the various uses of climate services.

Conditions and Outlook

Recent (September – October 2025) sea surface temperatures (SSTs) were below-average across the central and eastern equatorial Pacific Ocean and, along with atmospheric indicators such as stronger trade winds and increased cloudiness in the western Pacific, indicate La Niña or La Niña-like conditions. In the Indian Ocean, a negative Indian Ocean Dipole is present.
International climate outlooks predict weak or moderate La Niña conditions for December 2025 to February 2026. After DJF 2025/2026, most models indicate a transition from La Niña to ENSO-neutral conditions, although there remains a possibility that La Niña may persist beyond early 2026. The Indian Ocean Dipole (IOD) is likely to return to neutral during December 2025.
The onset of the 2025/2026 Northeast monsoon season has been or is expected to be near- or later than average for much of the northern ASEAN region. The onset for much of the southern ASEAN region is predicted to be near-average. The strength of the Northeast Monsoon is predicted to be near-average over most of Southeast Asia.

During DJF 2025/2026, tropical cyclone frequency is predicted to be above average around the Philippine Sea, and near-average for the Bay of Bengal, and South China Sea.

RAINFALL

For the upcoming boreal (Northern Hemisphere) winter season (DJF 2025/2026):

Over the Maritime Continent, near- to above-normal or above-normal rainfall is predicted for much of the eastern half of the region, including most of the Philippines, Brunei Darussalam, Sabah, and Timor-Leste. One exception is over the northwestern Philippines where below- to near-normal rainfall is predicted. For the western half, most of the region is predicted to experience either below- to near-normal or near-normal rainfall, including near-normal rainfall over Singapore, Peninsular Malaysia, and parts of East Malaysia.

Across Mainland Southeast Asia, near- to above-normal rainfall is predicted over parts of southern Mainland Southeast Asia, including southern Thailand, southern and eastern Cambodia, southern Viet Nam, as well as central Myanmar. Near- to below-normal rainfall is predicted over northern parts, including northern Myanmar, Lao PDR, and Viet Nam. Elsewhere, near-normal rainfall is predicted.

TEMPERATURE

For the upcoming boreal (Northern Hemisphere) winter season (DJF 2025/2026):

Over the Maritime Continent, near-to above-normal or above-normal temperature is predicted, apart from over the northern Philippines where near-normal temperature is predicted.

Over Mainland Southeast Asia, most of the region is predicted to experience near-normal temperature, apart from northern Myanmar, northern Thailand, central and southern Lao PDR, and most of Cambodia where near-to above-normal or above-normal temperature is predicted.

¹For this outlook, near-to above-normal temperature corresponds to 50% probability of above-normal temperature, 40% near-normal, and 10% below-normal. Further information is in the consensus maps.

Refer to Annex A for reference on what is meant by “above, near, or below normal” in the outlook. For more information on the boreal (Northern Hemisphere) summer monsoon outlook and further updates on the national scale, the relevant NMHSs should be consulted (see Annex B).

CONSENSUS MAPS FOR DJF 2025/2026

The following maps provide the probabilistic outlooks for DJF 2025/2026 season in terms of tercile categories of “Above Normal” (AN: upper tercile), “Near Normal (NN: middle tercile) and “Below Normal” (BN: lower tercile).

PROBABILISTIC RAINFALL OUTLOOK

PROBABILISTIC TEMPERATURE OUTLOOK

Meeting Documents

ASEANCOF-25 Outlook Bulletin

Acknowledgements

ASEANCOF would like to convey its appreciation to the NMHSs of the ASEAN Member States for sharing their national level forecasts, the Global Producing Centres, the Southeast Asia Regional Climate Centre – Network, RIMES, UN ESCAP, FAO, USQ, GHHIN Southeast Asia Hub and other partners of ASEANCOF for sharing their products and expertise, and the World Meteorological Organization Regional Office in Asia and the Southwest Pacific (WMO-RAP) for their continued support of ASEANCOF. The Forum would also like to thank MOWRAM Cambodia for hosting the forum, with support from RIMES, CREWS and WISER Asia Pacific for the funding support provided for the meeting.

Review of Regional Haze Situation for October 2025

1.1 The Southwest Monsoon transitioned to the inter-monsoon conditions during October 2025, with the monsoon rainband shifted towards the Equator. This was characterised by light low-level winds with variable directions over most of the ASEAN region in October (Figure 1). The South China Sea and the northern parts of the Philippines experienced strong winds at times, influenced by Typhoon Matmo and Tropical Storm Fengshen (Figures 9 and 10).

1.2 Showers prevailed over most of the ASEAN region in October 2025 (Figure 1). With increased shower activities, the Alert Level for the Southern ASEAN region was downgraded from Level 1 to Level 0 on 22 October 2025, marking the end of the dry season for the region. Heavy rainfall was observed over the Philippines and the central parts of Viet Nam due to Typhoon Matmo and Tropical Storm Fengshen (Figures 9 and 10).

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

1.3 In October 2025, the hotspot counts for the ASEAN region were generally lower than or comparable to those recorded in the same month during previous years (Figure 2 and 3).

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

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

1.4 Persistent and intense hotspots were detected mostly in the central and southern parts of Sumatra, the central and eastern parts of Kalimantan and parts of Sulawesi and the Lesser Sunda Islands (Figures 4 and 5). Slight to moderate localised smoke plumes were observed over the central and southern parts of Sumatra and the eastern parts of Kalimantan during brief periods of dry weather (Figures 6, 7 and 8).

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

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

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

Figure 7: Slight to moderate localised smoke plumes observed over the eastern parts of Kalimantan on 15 October 2025. (Source: Himawari-9 satellite surveillance)

Figure 8: Slight to moderate localised smoke plumes were observed over the central and southern parts of Sumatra on 31 October 2025. (Source: Himawari-9 satellite surveillance)

Figure 9: Typhoon Matmo over the northern parts of the South China Sea (Source: NOAA-21 satellite surveillance)

Figure 10: Tropical Storm Fengshen over the South China Sea (Source: NOAA-20 satellite surveillance)

November 5, 2025

Subseasonal Weather Outlook (10 – 23 November 2025)

Issued: 5 November 2025
First forecast week: 10 – 16 November 2025
Second forecast week: 17 – 23 November 2025

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over southern and southeastern Mainland Southeast Asia and the western equatorial region in Week 1 (10 – 16 November).

Wetter conditions are predicted over much of the southern and southeastern Maritime Continent in the next fortnight (10 – 23 November). Wetter conditions are also predicted over southern and southeastern Mainland Southeast Asia in Week 2 (17 – 23 November).

Warmer than usual temperatures are predicted over parts of the western and central equatorial region in the next fortnight (10 – 23 November). Cooler than usual temperatures are predicted over parts of Mainland Southeast Asia in Week 2 (17 – 23 November).

A Madden-Julian Oscillation (MJO) signal propagated across the Maritime Continent (Phases 4 and 5) during the last week of October. Most models predict this signal to reach the Western Pacific (Phase 6) by the start of the forecast period and then continue propagating eastwards. Some models predict the signal to weaken over the Western Pacific (Phase 7) in Week 2 (17 – 23 November).