Seasonal Forecast for October- December 2026
Updated 5 October 2026
In September 2026, Southwest Monsoon conditions prevailed over the ASEAN region, with prevailing winds blowing mostly from the southeast or southwest. During this period, the southern ASEAN region continues to experience its dry season, while the northern ASEAN region experiences its wet season. Towards the end of October, the Southwest Monsoon is expected to gradually transition into inter-monsoon conditions, characterised by light and variable winds. Rainfall is anticipated to return over the southern ASEAN region as the monsoon rainband shifts southwards towards the Equator.
For October 2026, below-normal rainfall is predicted for much of the Maritime Continent, with the highest probability over the southern half of the region. During October – December (OND), models predict a high chance of below-normal rainfall over parts of eastern Mainland Southeast Asia and much of the Maritime Continent, apart from the northwestern portion and parts of western Borneo. El Niño conditions are present and predicted to strengthen in October-November 2026. El Niño conditions tend to lead to an increased chance of below-normal rainfall for much of the Maritime Continent region and parts of eastern Mainland Southeast Asia at this time of the year. During October and OND 2026, above-normal temperature is predicted over most of the ASEAN region.
Under El Niño conditions and with below-normal rainfall expected across most of the southern ASEAN region, the hotspot and smoke haze situation is expected to remain escalated in the region. The risk of transboundary haze persists under prevailing southeasterly or southwesterly wind conditions. Increased showers under the inter-monsoon conditions towards the end of October could start to alleviate the hotspot and smoke haze situation over the region. Towards the end of the year, the northern ASEAN region is expected to enter its dry season, which could lead to a rise in hotspot and smoke haze activity, particularly over areas experiencing below-normal rainfall conditions.
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 2026, below-normal rainfall is predicted for most of the Maritime Continent, with the highest probability over the southern Maritime Continent.
For October 2026, below-normal rainfall is predicted over most of the Maritime Continent based on the multi-model ensemble (Figure 1). The highest probability of below-normal rainfall is over the southern half of the Maritime Continent. Most of the models (more than six models) predict below-normal rainfall as the dominant tercile for most of the Maritime Continent, apart from northern and western parts of Borneo, where a slight increase in chance of above-normal rainfall is predicted. Model skill for below-normal rainfall is good over the southern half and most of the northeastern parts of the Maritime Continent and low to moderate elsewhere. Model skill for above-normal rainfall over the northwestern Maritime Continent is low to moderate.
For Mainland Southeast Asia, a slight increase in chance of below-normal rainfall is predicted for the southeast and northwest parts of the region (Figure 1), where much or most of the models (four or more models) agree on below-normal tercile as the dominant tercile (Figure 2). Elsewhere in the region, over the central parts no dominant tercile is predicted and over parts of the northern region a slight increase in chance of above-normal rainfall is predicted by much of the models (four to six models). Model skill for below-normal rainfall is moderate to good over southeastern Mainland Southeast Asia and low elsewhere in the region. Model skill for above-normal rainfall is low to moderate over Mainland Southeast Asia.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for October 2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for October 2026. 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 3: Average climatological rainfall’s lower tercile boundary for October based on CHIRPS (reference period: 1991-2020). | Figure 4: 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 2026, models predict below-normal rainfall over much of the Maritime Continent and parts of eastern Mainland Southeast Asia.
For OND 2026, a high probability of below-normal rainfall is predicted over the southern and most of the eastern Maritime Continent based on the multi-model ensemble (Figure 1) with high agreement between the models (more than six models) on below-normal rainfall (Figure 2). Over the northwestern Maritime Continent and parts of western Borneo, increased probability of above-normal rainfall is predicted with much or most models in agreement (four or more models). Model skill for below-normal rainfall is good over most of the Maritime Continent where a high probability of below-normal rainfall is predicted.
For Mainland Southeast Asia, a slight increase in chance of below-normal rainfall is predicted over parts of the eastern and northwestern regions (Figure 1), where much or most of the models (four or more models) agree on below-normal tercile as the dominant tercile (Figure 2). Elsewhere in the region, over the central parts no dominant tercile is predicted and over parts of the northern region, a slight increase in chance of above-normal rainfall is predicted by much of the models (four to six models). Model skill is low for above-normal rainfall over northern Mainland Southeast Asia. For below-normal rainfall, model skill is moderate over eastern Mainland Southeast Asia, and low elsewhere.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for OND 2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for OND 2026. 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 3: Average climatological rainfall’s lower tercile boundary for OND based on CHIRPS (reference period: 1991-2020). | Figure 4: Average climatological rainfall’s upper tercile boundary for OND 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 2026, a high chance of above-normal temperature is predicted for most of Southeast Asia.
For October 2026, a high chance of above-normal temperature is predicted over most of Southeast Asia, based on the multi-model ensemble (Figure 1). The main exception is over the southeastern Maritime Continent where a mix of below- to above-normal temperature is predicted. For this region, much of the models agree on the most likely tercile (four to six models). Outside of southeastern Maritime Continent, most of the models (more than six models, Figure 2) predict above-normal as the most likely tercile. Model skill for predicting above-normal temperature is moderate to good over Southeast Asia, and good for below-normal temperature over the southeastern Maritime Continent.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for October 2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for October 2026. 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 3: 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 2026, a high chance of above-normal temperature is predicted for Southeast Asia.
For OND 2026, above-normal temperature is predicted over most of Southeast Asia, based on the multi-model ensemble (Figure 1). Most models (more than six) are in agreement that above-normal is the most likely tercile for Southeast Asia. Model skill for predicting above-normal temperature is good, apart from over northwestern Mainland Southeast Asia and the southeastern Maritime Continent, where skill is moderate.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for OND 2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for OND 2026. 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 3: 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.