Seasonal Forecast for August – October 2025
Updated 1 August 2025
During August to October (ASO) 2025, Southwest Monsoon typically dominates the ASEAN region. The dry season of the southern ASEAN region is expected to continue with the prevailing low-level winds blowing mostly from the southeast except for areas close to the Equator where the prevailing winds are blowing from the south. The monsoon rainband situated over the north of the Equator brings widespread showers over the northern ASEAN region, where the prevailing low-level winds blow mainly from the southwest.
For the ASO 2025 period, above-normal rainfall is predicted for much of the Maritime Continent. ENSO neutral conditions are predicted to persist in August, with the potential for La Niña conditions to develop from September – October 2025. The Indian Ocean Dipole (IOD) is neutral, with models predicting neutral conditions to persist in August and then either neutral or negative IOD conditions during September – October 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 ASEAN region for ASO 2025.
During the outlook period, while near-normal or above-normal rainfall is expected over most parts of the southern ASEAN region, hotspots with smoke plumes can still occur, especially in areas facing prolonged dry conditions, with a risk of transboundary haze occurrence. For the northern ASEAN region, the number of hotspots is estimated to remain low under the prevailing wet weather 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 August 2025, above-normal rainfall is predicted over the southern and eastern Maritime Continent.
For August 2025, above-normal rainfall is predicted over most of the southern and eastern Maritime Continent based on the multi-model ensemble (Figure 1), with most models (more than six models, Figure 2) predicting above-normal rainfall as the dominant tercile for the southern region. A mix of below- to above-normal rainfall is predicted over northwestern Mainland Southeast Asia by some of the models (4 – 6 models in agreement). Elsewhere, no dominant tercile is predicted by the multi-model ensemble. Model skill is good for predicting above-normal rainfall over the southern Maritime Continent, and low to moderate for predicting below- and above-normal rainfall for the other mentioned regions.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for August 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for August 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 August based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for August 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 ASO 2025, models predict above-normal rainfall over much of the Maritime Continent.
For ASO 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 much of the southern, central and eastern parts of the region (more than six models, Figure 2). Below-normal rainfall is predicted over the northwestern Maritime Continent with low skill and moderate agreement between the models. Model skill for predicting above-normal rainfall is good for the southern, central and southeastern Maritime Continent and low to moderate elsewhere.
For Mainland Southeast Asia, above-normal rainfall is predicted over the eastern half and no dominant tercile is predicted over the western half. There is moderate agreement (4-6 models) for the above-normal rainfall and little agreement (less than 3 models) for the no dominant tercile over the western half (Figure 2). Model skill is low to moderate for Mainland Southeast Asia.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for ASO 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for ASO 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 ASO based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for ASO 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 August 2025, above-normal temperature is predicted over Southeast Asia.
For August 2025, above-normal temperature is predicted over Southeast Asia, based on the multi-model ensemble (Figure 1). The models predict a higher likelihood of above-normal temperature over the Maritime Continent as compared to Mainland Southeast Asia. Most of the models (more than six models, Figure 2) predict above-normal temperature as the most likely tercile. Model skill for predicting above-normal temperature is relatively good for most of Southeast Asia.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for August 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for August 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 August 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 ASO 2025, above-normal temperature is predicted over Southeast Asia.
For ASO 2025, an increase in chance of above-normal temperature is predicted for Southeast Asia, based on the multi-model ensemble (Figure 1). The probability of above-normal temperature is high for most of the region, except over northeast Mainland Southeast Asia and southern Borneo. Most models (more than six models, Figure 2) predict above-normal temperature as the most likely tercile. 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 ASO 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for ASO 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 ASO 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.