Seasonal Forecast for June – August 2024

Updated 5 June 2024

In June 2024, the Southwest Monsoon is expected to be established over the ASEAN region and persist throughout the outlook period. The prevailing winds typically blow from the southeast or southwest over the region during this period. The Southwest Monsoon is also characterised with wet weather conditions over the northern ASEAN region as the monsoon rainband shifts further north from the Equator, also identified as the traditional wet season for the northern ASEAN region. On the other hand, the southern ASEAN region typically experiences its traditional dry season marked by drier conditions over most parts of the region compared to the other times of the year.

For June to August (JJA) 2024 period, models predict an increased chance of above-normal rainfall over the equatorial region, with below-normal rainfall predicted for much of the southern Maritime Continent region in June-August period. Above-normal temperature is predicted for the ASEAN region for JJA 2024. ENSO state has transitioned to neutral conditions and is likely to remain neutral during June-July 2024. The Indian Ocean Dipole (IOD) is neutral, with models predicting a potential for a weak and short-lived positive IOD in the next few months. The effect of El Niño conditions may still be present for a while after its decay, with above normal temperature predicted for the region.

Despite the above-normal rainfall forecast over most parts of the southern ASEAN region during the outlook period, the hotspot activity and the likelihood of smoke haze occurrence can still be expected to increase as the region experiences its traditional dry season, especially over areas in the southern Maritime Continent where below-normal rainfall are forecast. Coupled with the expected southeasterly or southwesterly winds, there may be risks of transboundary smoke haze occurrences over the region. Based on the current outlook for climate drivers, the risk is expected to be lower than in 2023 where extended drier and warmer conditions occurred due to El Niño conditions and a positive IOD. In the northern ASEAN region, the hotspot and smoke haze situation is expected to remain suppressed under the 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 June 2024, above-normal rainfall is predicted for much of the eastern half of the equatorial region, with below-normal predicted for much of the southern Maritime Continent.

 

For June 2024, above-normal rainfall is predicted for much of the central and eastern parts of the equatorial region based on the multi-model ensemble (Figure 4). The ECMWF model (Figure 2) shows the highest confidence of above-normal rainfall across this region, followed by UK Met Office model (Figure 3), and the NCEP model (Figure 1). For above-normal rainfall over the equatorial region, models’ skill is moderate to good for the ECMWF and UK Met Office models, and low to moderate for the NCEP model.

Below-normal rainfall is predicted over much of the southern Maritime Continent and the Philippines based on the multi-model ensemble (Figure 4). The UK Met Office model (Figure 3) has the highest confidence for below-normal rainfall over the southern Maritime Continent and the Philippines, followed by the ECMWF model (Figure 2). The NCEP model (Figure 1) agrees with drier conditions over the southern Maritime Continent, but not for the Philippines. The models’ skill for below-normal rainfall is overall moderate over the southern Maritime Continent and the Philippines.

Elsewhere, either no dominant tercile is predicted (most parts of Mainland Southeast Asia and the western equatorial region) or model skill is low (southern parts of Mainland Southeast Asia).

Figure 1: Rainfall tercile summary predictions of NCEP model for June 2024 (contains modified Copernicus C3S information). Figure 2: Rainfall tercile summary predictions of ECMWF model for June 2024 (contains modified Copernicus C3S information).

Figure 3: Rainfall tercile summary predictions of UK Met Office model for June 2024 (contains modified Copernicus C3S information). Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for June 2024 (contains modified Copernicus C3S information).

Figure 5: Average climatological rainfall’s lower tercile boundary for May based on CHIRPS (reference period: 1991-2020). Figure 6: Average climatological rainfall’s upper tercile boundary for May 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 2024, above-normal rainfall is predicted for the equatorial region and southern parts of Mainland Southeast Asia, with below-normal rainfall predicted for the southern Maritime Continent.

 

For JJA 2024, above-normal rainfall is predicted for the equatorial region based on the multi-model ensemble (Figure 4). All three models predict above-normal rainfall with high confidence over Borneo and the eastern equatorial region (Figures 1 – 3). The ECMWF and NCEP models show also moderate to high confidence for above-normal rainfall over the western Maritime Continent, while the UK Met Office model predicts near- to above-normal rainfall. Models’ skill is overall good for above-normal rainfall over the equatorial region.

Elsewhere in the Maritime Continent, a mix of below- to near-normal rainfall is predicted based on the multi-model ensemble (Figure 4). The ECMWF and UK Met Office models agree with an increase in chance of below-normal rainfall over the northern half of the Philippines (Figures 2 – 3), while the NCEP model predicts a higher chance of near-normal rainfall for this region. For the southern Maritime Continent, the ECMWF and UK Met Office models predict a high chance of below-normal rainfall, while the NCEP model predicts near-normal rainfall. The models’ skill for below-normal rainfall is overall moderate over Philippines and the southern Maritime Continent.

Over Mainland Southeast Asia, the models predict above-normal rainfall for the southern part of the region and with a disagreement between the models or no dominant tercile elsewhere. Model skill is generally low for Mainland Southeast Asia at this time of the year, apart from over the southern parts, where model skill is low to moderate.

Figure 1: Rainfall tercile summary predictions of NCEP model for JJA 2024 (contains modified Copernicus C3S information). Figure 2: Rainfall tercile summary predictions of ECMWF model for JJA 2024 (contains modified Copernicus C3S information).

Figure 3: Rainfall tercile summary predictions of UK Met Office model for JJA 2024 (contains modified Copernicus C3S information). Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for JJA 2024 (contains modified Copernicus C3S information).

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 2024, above-normal temperature is predicted over the ASEAN region.

 

For June 2024, above-normal temperature is predicted over the ASEAN region based on the multi-model ensemble (Figure 4). All three models agree with high confidence on above-normal temperature over most of the region, with only the UK Met Office model predicting near-normal temperature for the southernmost part of the Maritime Continent (Figure 3). Models’ skill for predicting above-normal temperature is good over the ASEAN region.

Figure 1: Temperature tercile summary predictions of NCEP model for June 2024 (contains modified Copernicus C3S information). Figure 2: Temperature tercile summary predictions of ECMWF model for June 2024 (contains modified Copernicus C3S information).

Figure 3: Temperature tercile summary predictions of UK Met Office model for June 2024 (contains modified Copernicus C3S information). Figure 4: Temperature tercile summary predictions of multi-model ensemble model for June 2024 (contains modified Copernicus C3S information).

 

Figure 5: Average climatological temperature for Jun 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 2024, above-normal temperature is predicted over the ASEAN region.

 

For JJA 2024, above-normal temperature is predicted over the ASEAN region based on the multi-model ensemble (Figure 4). All three models agree with high confidence on above-normal temperature over most of the region, apart from over the southernmost part of the Maritime Continent where below- to near-normal temperature is predicted by the UK Met Office (Figure 3). Models’ skill for predicting above-normal temperature is relatively good for most of the ASEAN region.

Figure 1: Temperature tercile summary predictions of NCEP model for JJA 2024 (contains modified Copernicus C3S information). Figure 2: Temperature tercile summary predictions of ECMWF model for JJA 2024 (contains modified Copernicus C3S information).

Figure 3: Temperature tercile summary predictions of UK Met Office model for JJA 2024 (contains modified Copernicus C3S information). Figure 4: Temperature tercile summary predictions of multi-model ensemble model for JJA 2024 (contains modified Copernicus C3S information).

 

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.