Seasonal Forecast for June – August 2026
Updated 3 June 2026
Inter-monsoon conditions typically transition gradually into the Southwest Monsoon in June, with prevailing winds shifting to blow mainly from the southeast or southwest. The northern ASEAN region typically experiences its traditional wet season due to an increase in shower activities as the monsoon rainband moves northwards. In contrast, the southern ASEAN region typically experiences its traditional dry season during the outlook period.
For June 2026, below- to near-normal rainfall is predicted over much of the southern ASEAN region. During June – August (JJA) 2026, below-normal rainfall is predicted to persist for the southern ASEAN region, while a mix of below- to above-normal rainfall is predicted for the northern ASEAN region. ENSO-neutral conditions are predicted to transition to El Niño conditions in June-July 2026. El Niño conditions tend to lead to an increased chance of below-normal rainfall for much of the southern ASEAN region during June – August.
As the southern ASEAN region enters its traditional dry season, and with below-normal rainfall expected over most parts of the region, an increase in hotspot and smoke haze activity is expected. This can lead to a heightened risk of transboundary haze occurrence under the prevailing southeasterly or southwesterly winds in the region. The situation could intensify when El Niño conditions develop. The hotspot and smoke haze situation is expected to remain subdued over the Mekong sub-region as showers continue during the outlook period.
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 2026, below-normal rainfall is predicted over the Maritime Continent.
For June 2026, over the Maritime Continent, below-normal rainfall is predicted, based on the multi-model ensemble (Figure 1). The highest probability of below-normal rainfall is over the central and eastern parts of the equatorial region, where most of the models (more than six models, Figure 2) predict below-normal rainfall as the dominant tercile. Model skill for below-normal rainfall is moderate to good over the eastern equatorial region and low to moderate elsewhere over the Maritime Continent.
For Mainland Southeast Asia, no dominant tercile is predicted for most of the region. There is little agreement between models, apart from a few small regions where there is some agreement between the models (four to six models) regarding an increase in chance of above-normal rainfall (parts of southern and northeastern Mainland Southeast Asia). Model skill is low over both southern and eastern Mailand Southeast Asia.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for June 2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for June 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 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 2026, models predict below-normal rainfall for the southern ASEAN region, with a mix of below- and above-normal rainfall predicted over much of the northern ASEAN region.
For JJA 2026, an increased chance of below-normal rainfall is predicted for the southern ASEAN region, based on the multi-model ensemble (Figure 1). Most models (more than six models) are in agreement with below-normal as the dominant tercile for much of the region. Model skill is moderate to good over the eastern and central parts of the southern ASEAN region and low to moderate over the western part at this time of the year.
For the northern ASEAN region, a mix of below- and above-normal rainfall is predicted for much of the region, apart from the northwestern parts where no dominant tercile is predicted. Some models (4 – 6 models) are in agreement regarding an increase in chance of below- and above-normal rainfall. Model skill is low for both below- and above-normal rainfall, apart from over southern Mainland Southeast Asia, where skill is low to moderate.
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| Figure 1: Rainfall tercile summary predictions of the multi model ensemble for JJA 2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for JJA 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 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 2026, above-normal temperature is predicted most of the ASEAN region.
For June 2026, above-normal temperature is predicted over the ASEAN region, with the highest likelihood in the equatorial region, northeastern Maritime Continent, and southern parts of Mailand Southeast Asia, based on the multi-model ensemble (Figure 1). Most of the models (more than six models, Figure 2) predict above-normal temperature as the most likely tercile for almost the entire ASEAN region, apart from some of the southernmost part of the region. Model skill for predicting above-normal temperature is good for much of the region, apart from the northernmost part where it is low to moderate.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for June 2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for June 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 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 2026, models predict above-normal temperature over most of the ASEAN region.
For JJA 2026, above-normal temperature is predicted over most of the ASEAN region, apart from the southernmost part of the region where near- to above-normal temperature is predicted, based on the multi-model ensemble (Figure 1). Most models (more than six models) predict above-normal temperature as the most likely tercile apart from over the southernmost part where some models (four to six) agree that above-normal temperature is the most likely tercile (Figure 2). Model skill for predicting above-normal temperature is good at this time of the year.
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| Figure 1: Temperature tercile summary predictions of the multi model ensemble for JJA 2026 (contains modified Copernicus C3S information). | Figure 2: Number of models in agreement in the multi-model ensemble for the dominant tercile for JJA 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 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.