Seasonal Forecast for June – August 2025
Updated 4 June 2025
The inter-monsoon period typically transitions into the Southwest Monsoon over the ASEAN region in June 2025, which will continue throughout the outlook period. During this time, the prevailing winds typically blow from the southeast or southwest across the region. The northern ASEAN region experiences its traditional wet season, as the monsoon rainband moves northward from the Equator, bringing wet weather over the region. In contrast, the southern ASEAN region typically experiences its traditional dry season during this period, with most areas experiencing drier conditions compared to other times in the year.
For June 2025, above-normal rainfall is predicted for much of the southern Maritime Continent. The above-normal rainfall is predicted to persist during June to August (JJA) and extend to cover most of the southern ASEAN region. 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 June, with these conditions predicted to persist throughout JJA 2025.
Despite forecasts of above-normal rainfall across much of the southern ASEAN region, the risk of hotspot and smoke haze occurrence is still expected to increase as the region enters its traditional dry season, particularly over areas in the equatorial region where below-normal rainfall is forecast. Furthermore, the expected southeasterly or southwesterly winds may increase the risk of transboundary smoke haze occurrence across the southern ASEAN region. In the northern ASEAN region, wet weather conditions are likely to suppress the occurrence of fires and smoke haze.
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 June 2025, above-normal rainfall is predicted for much of the southern Maritime Continent.
For June 2025, above-normal rainfall is predicted for much of the southern Maritime Continent based on the multi-model ensemble (Figure 4). The NCEP, ECMWF and UK Met Office models (Figures 1, 2, and 3, respectively) predict an increased chance of above-normal rainfall over much of the region, with the highest probability over the southeastern Maritime Continent. Elsewhere in the Maritime Continent, models predict either mix of below- to near-normal or no dominant tercile rainfall. The model skill for above-normal rainfall moderate to good in the southern Maritime Continent and low to moderate elsewhere, while the skill for near-normal rainfall is low to moderate for the entire Maritime Continent.
For Mainland Southeast Asia, no dominant tercile is predicted for much of the region, based on the multi-model ensemble (Figure 4). The ECMWF model (Figure 2) predicts an increased chance of above-normal rainfall for parts of the eastern half Mainland Southeast Asia, while the UK Met Office model (Figure 3) predicts no dominant tercile, and the NCEP model (Figure 1) predicts a mix of near- to below-normal over parts of the region. Model skill is low for much of Mainland Southeast Asia at this time of the year.
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| Figure 1: Rainfall tercile summary predictions of NCEP model for June 2025 (contains modified Copernicus C3S information). | Figure 2: Rainfall tercile summary predictions of ECMWF model for June 2025 (contains modified Copernicus C3S information). |
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| Figure 3: Rainfall tercile summary predictions of UK Met Office model for June 2025 (contains modified Copernicus C3S information). | Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for June 2025 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological rainfall’s lower tercile boundary for June based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for June 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 JJA 2025, above-normal rainfall is predicted for much southern ASEAN region.
For JJA 2025, above-normal rainfall is predicted for much of the southern ASEAN region, with a slight increase in chance of below-normal rainfall over the northwestern portion, based on the multi-model ensemble (Figure 4). The UK Met Office and ECMWF models (Figures 3 and 2, respectively) predict above-normal rainfall over all of the eastern portion, while the NCEP model (Figure 1) predicts a mix of near- to above-normal rainfall for this region. For the northwestern portion, the NCEP model predicts the largest extent of below-normal rainfall covering with the highest confidence, while the ECMWF model predicts below- to near-normal rainfall, and the UK Met Office model predicts no increase in chance of below-normal rainfall over this region. Models’ skill is generally good for above-normal rainfall apart of over the Philippines, and moderate for below-normal rainfall over the western Maritime Continent.
For the northern ASEAN region, there is generally disagreement between the models (Figures 1 – 3). Overall, there is a slight increase in chance of above-normal rainfall over the central parts of Mailand Southeast Asia and the southern Philippines and no dominant tercile for much of the region based on the multi-model ensemble (Figure 4). Model skill is low to moderate for the northern ASEAN region at this time of the year.
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| Figure 1: Rainfall tercile summary predictions of NCEP model for JJA 2025 (contains modified Copernicus C3S information). | Figure 2: Rainfall tercile summary predictions of ECMWF model for JJA 2025 (contains modified Copernicus C3S information). |
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| Figure 3: Rainfall tercile summary predictions of UK Met Office model for JJA 2025 (contains modified Copernicus C3S information). | Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for JJA 2025 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological rainfall’s lower tercile boundary for JJA based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for JJA 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 June 2025, above-normal temperature is predicted over Southeast Asia.
For June 2025, above-normal temperature is predicted over Southeast Asia, with high confidence over the Maritime Continent and slightly lower confidence over Mailand Southeast Asia, based on the multi-model ensemble (Figure 4). All three models (Figures 1 – 3) predict a high likelihood of above-normal temperature over the Maritime Continent. For Mainland Southeast Asia, the models predict above-normal temperature, but with lower likelihood for much of the region. Models’ skill for predicting above-normal temperature is good for most of Southeast Asia, while the skill for near-normal temperature is moderate for most of Mainland Southeast Asia.
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| Figure 1: Temperature tercile summary predictions of NCEP model for June 2025 (contains modified Copernicus C3S information). | Figure 2: Temperature tercile summary predictions of ECMWF model for June 2025 (contains modified Copernicus C3S information). |
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| Figure 3: Temperature tercile summary predictions of UK Met Office model for June 2025 (contains modified Copernicus C3S information). | Figure 4: Temperature tercile summary predictions of multi-model ensemble model for June 2025 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological temperature for June 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 JJA 2025, above-normal temperature is predicted over Southeast Asia.
For JJA 2025, an increase in chance of above-normal temperature is predicted over all of Southeast Asia based on the multi-model ensemble (Figure 4). All three models agree with high confidence on above-normal temperature over the Maritime Continent. For Mainland Southeast Asia, the ECMWF and UK Met Office models (Figures 2 and 3) predict the highest chance of above-normal temperature, while the NCEP model is slightly less confident on above-normal temperature in the southern parts of the region (Figure 1). Models’ skill for predicting above-normal temperature is good over most of Southeast Asia.
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| Figure 1: Temperature tercile summary predictions of NCEP model for JJA 2025 (contains modified Copernicus C3S information). | Figure 2: Temperature tercile summary predictions of ECMWF model for JJA 2025 (contains modified Copernicus C3S information). |
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| Figure 3: Temperature tercile summary predictions of UK Met Office model for JJA 2025 (contains modified Copernicus C3S information). | Figure 4: Temperature tercile summary predictions of multi-model ensemble model for JJA 2025 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological temperature for JJA 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.