Seasonal Forecast for September – November 2025
Updated 7 October 2025
The southwest monsoon conditions over the ASEAN region persisted in September 2025 but is expected to transition to inter-monsoon conditions in October 2025. The prevailing southeasterly to southwesterly winds which had dominated the ASEAN region are likely to transition to light and variable winds. Traditionally, the equatorial region experiences increased wet weather activities as the monsoon rainband continues to shift southwards over the Equator.
For the October to December (OND) 2025 period, above-normal rainfall is predicted for much of the Maritime Continent and eastern Mainland Southeast Asia. There is the potential for La Niña conditions to develop in October – November 2025. There were signs of a negative Indian Ocean Dipole (IOD), with models predicting negative IOD conditions in October–November 2025. Both La Niña and negative IOD events tend to bring wetter conditions to parts of Southeast Asia. Above-normal temperature is predicted for most of the Maritime Continent and northwestern Mainland Southeast Asia for OND 2025.
Normal to above-normal rainfall is forecast for many parts of the southern ASEAN region during the outlook period of OND 2025, and consequently hotspot and haze activities over the region are expected to remain subdued, with a reduced risk of transboundary smoke haze. However, drier conditions are still expected over parts of Sumatra and Peninsular Malaysia due to below-normal rainfall forecast over the area, which can lead to the emergence of localised smoke plumes and clusters of isolated hotspots. Towards the end of the year, the traditional dry season for the northern ASEAN region is expected to set-in, which could lead to an increase in hotspot and smoke haze activity, particularly in the Mekong sub-region.
The qualitative outlook is assessed for the region in general and based on the latest runs from models provided by the SEA RCC-Network LRF node. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.
For October 2025, above-normal rainfall is predicted over most of the Maritime Continent and much of Mainland Southeast Asia.
For October 2025, above-normal rainfall is predicted over most of the Maritime Continent based on the multi-model ensemble (Figure 1), apart from over much of the western part. Most models (more than six models, Figure 2) predict above-normal rainfall as the dominant tercile for the southern and eastern region. Most models (more than six models) predict below-normal rainfall over the northwestern Maritime Continent.
For Mainland Southeast Asia, above-normal rainfall is predicted over much of the region. Most models (more than six models) predictabove-normal rainfall over the eastern part, with some models (4 – 6) predicting above-normal rainfall over central Mainland Southeast Asia. Elsewhere, no dominant tercile is predicted.
Model skill is good for predicting above-normal rainfall over the southern Maritime Continent, low to moderate for predicting above-normal rainfall elsewhere in Southeast Asia, and low to moderate for predicting below-normal rainfall over the western Maritime Continent.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for October 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for October 2025. Where there no dominant tercile, it refers to the number of models with near-normal tercile (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological rainfall’s lower tercile boundary for October based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for October based on CHIRPS (reference period: 1991-2020). |
The qualitative outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted. More outlook and verification plots, including for tercile and quintile probabilistic forecasts for rainfall, are in the “Model products and verification: NCEP, ECMWF, UK Met Office” on the SEA-RCC Network LRF Node webpages.
For OND 2025, models predict above-normal rainfall over much of the Maritime Continent and eastern Mainland Southeast Asia.
For OND 2025, above-normal rainfall is predicted for much of the Maritime Continent, based on the multi-model ensemble (Figure 1). The highest probability of above-normal rainfall is over the southern Maritime Continent. Most models agree on above-normal rainfall as the most likely tercile for the southern and eastern parts of the region (more than six models, Figure 2). Below-normal rainfall is predicted over the western half of the equatorial region, with most models (more than six models) in agreement over the northwestern Maritime Continent and some models (4 – 6) elsewhere.. Model skill for predicting above-normal rainfall is good for the southern, central and southeastern Maritime Continent and low to moderate elsewhere. Model skill for predicting below-normal rainfall is moderate over the northwestern Maritime Continent.
For Mainland Southeast Asia, above-normal rainfall is predicted apart from over the northern region. Most models agree on above-normal rainfall over the eastern portion (more than 6 models) with only some models agreeing for the central and western portion (4 – 6 models). No dominant tercile is predicted for most of northern Mainland Southeast Asia. Model skill is moderate to good for southeastern Mainland Southeast Asia and low to moderate elsewhere in the region.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for OND 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for OND 2025. Where there no dominant tercile, it refers to the number of models with near-normal tercile (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological rainfall’s lower tercile boundary for SON based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for SON based on CHIRPS (reference period: 1991-2020). |
The qualitative outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted. More outlook and verification plots, including for tercile and quintile probabilistic forecasts for rainfall, are in the “Model products and verification: NCEP, ECMWF, UK Met Office” on the SEA-RCC Network LRF Node webpages.
For October 2025, above-normal temperature is predicted over most of Southeast Asia.
For October 2025, above-normal temperature is predicted over most of Southeast Asia (Figure 1). The likelihood of above-normal temperature is high over much of the Maritime Continent and Mainland Southeast Asia. Most of the models (more than six models, Figure 2) predict above-normal temperature as the most likely tercile, apart from over parts of central Mainland Southeast Asia and parts of the central and southern Maritime Continent. Model skill for predicting above-normal temperature is relatively good for most of the Maritime Continent and moderate for Mainland Southeast Asia.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for October 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for October 2025. Where there no dominant tercile, it refers to the number of models with near-normal tercile (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological temperature for October based on ERA5 (reference period: 1991-2020). |
The qualitative outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted. More outlook and verification plots, including for tercile and quintile probabilistic forecasts for temperature, are in the “Model products and verification: NCEP, ECMWF, UK Met Office” on the SEA-RCC Network LRF Node webpages.
For OND 2025, above-normal temperature is predicted over most of the Maritime Continent and northwestern Mainland Southeast Asia.
For OND 2025, above-normal temperature is predicted over most of the Maritime Continent while a mix of below- to above-normal temperature is predicted over Mainland Southeast Asia (Figure 1). Over northwestern Mailand Southeast Asia and most of the Maritime Continent, most models (more than six models) predict above-normal temperature as the most likely tercile. Over parts of central and eastern Mainland Southeast Asia and the southwestern Maritime Continent, either no dominant, below-normal or near-normal temperature is predicted. There is less agreement between models for these regions, with only some models (4 – 6) predicting near-normal or below-normal temperature. Model skill for predicting above-normal temperature is good for most of Southeast Asia.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for OND 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for OND 2025. Where there no dominant tercile, it refers to the number of models with near-normal tercile (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological temperature for OND based on ERA5 (reference period: 1991-2020). |
The qualitative outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted. More outlook and verification plots, including for tercile and quintile probabilistic forecasts for temperature, are in the “Model products and verification: NCEP, ECMWF, UK Met Office” on the SEA-RCC Network LRF Node webpages.
Frequently Asked Questions
What is a seasonal forecast?
A seasonal forecast provides forecast information about the general weather conditions at seasonal timescales up to several months ahead. Long range predictions rely on predicting components of the atmosphere and the oceans which show variations at large spatial and temporal scales. Among these key components is the sea-surface temperature – an important indicator in the El Niño Southern Oscillation (ENSO) cycle.
Example of probabilistic long range forecast using the multi-model ensemble. For areas nearby Peninsular Malaysia, the forecast is showing a probability of 50-70% of rainfall being in the below-normal (33%) tercile range. (Source: WMO LC LRF)
To account for the chaotic nature of the atmosphere, seasonal forecast adopts a probabilistic approach and the forecast weather condition is presented as an average over an extended period of time, usually with reference to climatology.
ASMC carries out monthly seasonal forecast predictions based on various seasonal model forecasts from the leading meteorological centres, supplemented by individual assessments from respective countries in South East Asia. The skillfulness of seasonal forecast relies greatly on the performance of seasonal models, which differ from one place to another and for different seasons of the year.
Receiver operating characteristic (ROC) score of UK GloSea5 seasonal hindcast for above-normal precipitation scenario for Dec – Feb (left) and May – Jul (right) over Asia region. Higher ROC score (indicated in red) means better model skill. (Source: UK Met Office)
For example, one way to assess the seasonal model skills is to examine the ROC score. From the figures above, we can see that ROC score map differs greatly from one season to another. During the period from Dec to Feb, a high ROC score region is observed mainly over the Philippines whereas during the period from May to Jul, a high ROC score region is observed over the near equatorial region such as Peninsular Malaysia and Sumatra.