Seasonal Forecast for December 2025 – February 2026
Updated 2 December 2025
The inter-monsoon conditions typically continue to transition gradually to the Northeast Monsoon over the ASEAN region in December. As the monsoon rainband shifts towards the south of the Equator, the prevailing winds over most of the ASEAN region are likely to strengthen and blow mainly from the northeast or northwest. The prevailing winds could further intensify at times during the Northeast Monsoon surge. During the outlook period, the northern and southern ASEAN region typically experience their dry and wet seasons respectively.
For the December 2025 to February 2026 (DJF) period, above-normal rainfall is predicted for much of the northeastern Maritime Continent. Current ENSO state is La Niña conditions, with weak to moderate La Niña conditions predicted for November 2025 – January 2026, with some models predicting the La Nina conditions to continue into February – March 2026. A negative Indian Ocean Dipole (IOD) is present and is predicted to persist until December 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 for DJF 2025-2026.
The dry season for the northern ASEAN region is likely to begin towards the end of the year. While above-normal rainfall is expected over some parts of the region, the hotspot and smoke haze situation could still escalate, particularly in fire-prone areas, under the overall dry conditions in the region. Over the southern ASEAN region, the overall hotspot and smoke haze situation is forecast to remain subdued under the prevailing wet weather conditions. However, isolated hotspots with smoke plumes could develop when the region experiences occasional drier conditions, particularly during the dry phase of the Northeast Monsoon typically occurring during late January and February.
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 December 2025, above-normal rainfall is predicted over the northeastern and southern Maritime Continent as well as eastern parts of Mainland Southeast Asia.
For December 2025, below-normal rainfall is predicted over parts of the central and western Maritime Continent based on the multi-model ensemble (Figure 1), with above-normal rainfall over northeastern and parts of the southern regions. Most models (more than six models, Figure 2) predict above-normal rainfall as the dominant tercile for the northeastern regions and below-normal rainfall as the dominant tercile over central Borneo.
For Mainland Southeast Asia, above-normal rainfall is predicted over eastern most region and a mix of below-normal rainfall and no dominant tercile elsewhere. Most models predict above-normal rainfall for the eastern region, and at least some models (4 – 6) predict below-normal rainfall over the northeastern and southern most regions.
Model skill is good for predicting above-normal rainfall over the northeastern Maritime Continent and southeastern Mainland Southeast Asia. Model skill is low to moderate elsewhere in Southeast Asia.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for December 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for December 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 December based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for December 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 DJF 2025-2026, models predict above-normal rainfall over much of the northeastern Maritime Continent.
For DJF 2025-2026, above-normal rainfall is predicted for the northeastern Maritime Continent, with below-normal predicted over parts of the central Maritime Continent and no dominant tercile generally elsewhere, based on the multi-model ensemble (Figure 1). Most models agree on above-normal rainfall as the most likely tercile for the northeastern parts of the region (more than six models, Figure 2). For below-normal rainfall predicted in the Maritime Continent, most models (more than six models) agree with each other for central Borneo with at least some models (4 – 6) elsewhere.
For Mainland Southeast Asia, above-normal rainfall is predicted over the eastern regions with no dominant tercile elsewhere. Most models (more than 6 models) agree on the above-normal rainfall over the eastern portion.
Model skill is good over the northeastern Maritime Continent and eastern Mainland Southeast Asia for predicting above-normal rainfall. Model skill is poor to moderate elsewhere in the region.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for DJF 2025 -2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for DJF 2025 – 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 5: Average climatological rainfall’s lower tercile boundary for DJF based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for DJF 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 December 2025, above-normal temperature is predicted over most of the Maritime Continent, with below- to near-normal temperature predicted over much of central and eastern Mainland Southeast Asia.
For December 2025, above-normal temperature is predicted over most of the Maritime Continent and northwestern Mainland Southeast Asia (Figure 1). The likelihood of above-normal temperature is high over much of the eastern Maritime Continent. Most of the models (more than six models, Figure 2) predict above-normal temperature as the most likely tercile for the mentioned regions. Model skill for predicting above-normal temperature is relatively good for most of the Maritime Continent and moderate for northwestern Mainland Southeast Asia.
Elsewhere, below- to near-normal temperature is predicted over central and eastern Mainland Southeast Asia (Figure 1), with generally some models (4 – 6) in agreement with each other (Figure 2). Model skill for predicting near-to below normal temperature is low to moderate for Mainland Southeast Asia.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for December 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for December 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 December 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 DJF 2025-2026, above-normal temperature is predicted over most of the Maritime Continent, with near-normal temperature predicted for central and eastern Mainland Southeast Asia.
For DJF 2025-2026, above-normal temperature is predicted over most of the Maritime Continent as well as northwestern Mainland Southeast Asia and parts of northeastern Mainland Southeast Asia. Most models (more than six models) predict above-normal temperature as the most likely tercile over most of the Maritime Continent and northwestern Mainland Southeast Asia. Model skill for predicting above-normal temperature is good for most of Southeast Asia.
A mix of near-normal temperature and no dominant tercile is predicted over central and eastern Mainland Southeast Asia (Figure 1). There is less agreement between models for the region predicting near-normal temperature. Model skill is generally moderate for predicting near-normal temperature for the mention region.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for DJF 2025-2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for DJF 2025-2026. 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 5: Average climatological temperature for DJF 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.