Seasonal Forecast for July – September 2025
Updated 2 July 2025
The Southwest Monsoon conditions, which became established in June 2025, are expected to continue through the outlook period of July – September (JAS) 2025 with the prevailing low-level winds blowing mainly from the southeast or southwest. As the monsoon rain band is situated north of the Equator during this period, the southern ASEAN region typically experiences its traditional dry season while wet weather is typical over the northern ASEAN region.
For July 2025, above-normal rainfall is predicted for much of the southern Maritime Continent. The above-normal rainfall is predicted for much of the Maritime Continent during July to September (JAS). ENSO neutral conditions are predicted to persist until at least July – August 2025. The Indian Ocean Dipole (IOD) is currently neutral. Above-normal temperature is predicted for Southeast Asia for July, with these conditions predicted to persist throughout JAS 2025.
Despite forecast of above-normal rainfall across much of the southern ASEAN region during the outlook period, the risk of transboundary smoke haze occurrence remains as hotspots with smoke plumes can still be expected over the fire-prone areas in the region, especially during extended periods of drier weather. In the northern ASEAN region, the hotspot activity is expected 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 July 2025, an increased chance of above-normal rainfall is predicted for the southern Maritime Continent.
For July 2025, above-normal rainfall is predicted for 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. For the northwestern Maritime Continent and southern Mainland Southeast Asia, below-normal rainfall is predicted by some of the models (4 – 6 models in agreement). Model skill is moderate to good for predicting above-normal rainfall over the southern Maritime Continent, and low to moderate for predicting below-normal rainfall for the mentioned regions.
For most of the rest of the Maritime Continent as well as Mainland Southeast Asia, there is little to no agreement on the dominant tercile (less than four models in agreement, Figure 2). Model skill is moderate for the Maritime Continent outside of the southern region, and low to moderate for Mainland Southeast Asia.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for July 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for July 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 July based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for July 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 JAS 2025, above-normal rainfall is predicted for much of the Maritime Continent.
For JAS 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 eastern Maritime Continent. Most models agree on above-normal rainfall as the most likely tercile for much of the southern half of the region (more than six models, Figure 2). Model skill for predicting above-normal rainfall is good for the southern half of the Maritime Continent and low to moderate elsewhere.
For Mainland Southeast Asia, there is little to no agreement on the dominant tercile over most of the region (less than four models in agreement, 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 JAS 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for JAS 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 JAS based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for JAS 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 July 2025, above-normal temperature is predicted over Southeast Asia.
For July 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 July 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for July 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 July 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 JAS 2025, above-normal temperature is predicted over Southeast Asia.
For JAS 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. 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 JAS 2025 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for JAS 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 JAS 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.