Seasonal Forecast for June-July-August 2019

Updated 3 June 2019

Summary of Outlook

The region usually transitions from the inter-monsoon to the Southwest Monsoon around June. In the northern ASEAN region, the Southwest Monsoon is associated with the traditional rainy season while in the southern ASEAN region, this season is also the traditional dry season, and it is usually drier compared to other seasons of the year. The prevailing winds in the ASEAN region typically blow from the southeast or southwest.

Above-normal temperatures can be expected over most parts of the ASEAN region during the Jun-Jul-Aug 2019 season, in particular over the equatorial and northern ASEAN region.

Below-normal rainfall can be expected mainly over the southern ASEAN region. Based on the model outlooks, some parts of the northern ASEAN region may experience above-normal rainfall (southern parts of Myanmar, Thailand, Cambodia, and Viet Nam). There is no clear trend for the rest of the region.

Hotspot activities in the northern ASEAN region are expected to remain generally subdued. In the southern ASEAN region, extended periods of dry weather may contribute to an escalation in hotspot activities over the fire-prone provinces of Sumatra and Kalimantan. This could lead to the occurrence of transboundary haze affecting parts of the region. Typically, most hotspots emerge in northern and central Sumatra and western Kalimantan in the early part of the traditional dry season.

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.

For June 2019, below-normal rainfall is favoured over most of southern Southeast Asia and northern Philippines. Elsewhere, predictions either are not consistent between models, or have low skill.

 

Over southern Southeast Asia, all three models – NCEP CFSv2, ECMWF and the UK Met Office (Figures 1a-c) predict generally an increased chance of below-normal rainfall. The higher probabilities of below-normal rainfall are over regions south of the Equator, with moderate to high skill. Nearer to the equator, the models are less confident of below-normal rainfall, which corresponds to regions where there is only low to moderate skill scattered.

For northern Southeast Asia, the three models differ in their predictions, except for northern Philippines where below-normal rainfall is predicted. Notwithstanding, model skill for June over land is generally poor over this region (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office”).

Rainfall Tercile Summary of NCEP model.

Rainfall Tercile Summary of ECMWF model.

Figure 1a: Rainfall tercile summary predictions of NCEP model for June 2019. Figure 1b: Rainfall tercile summary predictions of ECMWF model for June 2019 (contains modified Copernicus C3S information).

Rainfall Tercile Summary of UK Met Office model.

Rainfall Tercile Summary of MME model.

Figure 1c: Rainfall tercile summary predictions of UK Met Office model for June 2019 (contains modified Copernicus C3S information). Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for June 2019 (contains modified Copernicus C3S information).

For JJA 2019, below-normal rainfall is favoured mainly over southern Southeast Asia. Some parts of northern Southeast Asia (southern parts of Myanmar, Thailand, Cambodia, and Vietnam are predicted to experience above-normal rainfall).

 

For JJA 2019, all three models – NCEP CFSv2, ECMWF and the UK Met Office (Figures 2a-c) predict a higher likelihood of below-normal rainfall over southern Southeast Asia. The JJA outlook is different from the previous MJJ 2019 outlook, which favoured above-normal conditions especially around the equatorial region. The models’ skill for rainfall is relatively good over southern Southeast Asia.

There is no consistent prediction for most of northern Southeast Asia, although there is some increase in likelihood for above-normal rainfall for select regions (e.g. southern parts of Myanmar, Thailand, Cambodia, and Vietnam). Models’ skill scores are also low for the JJA season for this region (NCEP, ECMWF, UK Met Office).

Rainfall Tercile Summary of NCEP model.

Rainfall Tercile Summary of ECMWF model.

Figure 2a: Rainfall tercile summary predictions of NCEP model for JJA 2019. Figure 2b: Rainfall tercile summary predictions of ECMWF model for JJA 2019 (contains modified Copernicus C3S information).

Rainfall Tercile Summary of UK Met Office model.

Rainfall Tercile Summary of MME model.

Figure 2c: Rainfall tercile summary predictions of UK Met Office model for JJA 2019 (contains modified Copernicus C3S information). Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for JJA 2019 (contains modified Copernicus C3S information).

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 2019, above-normal temperature is favoured over most parts of Southeast Asia, particularly north of the Equator.

 

For June 2019, all three models – NCEP CFSv2, ECMWF and the UK Met Office predict above-normal temperature over most parts of the Southeast Asia (Figures 1a-c), with higher probabilities north of the Equator.

Over most parts of Southeast Asia, the models’ skill scores for predicting above-normal temperature is generally very good (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office”).

Temperature tercile Summary of NCEP model.

Temperature tercile Summary of ECMWF model.

Figure 1a: Temperature tercile summary predictions of NCEP model for June 2019. Figure 1b: Temperature tercile summary predictions of ECMWF model for June 2019 (contains modified Copernicus C3S information).

Temperature tercile Summary of UK Met Office model.

Temperature tercile Summary of MME model.

Figure 1c: Temperature tercile summary predictions of UK Met Office model for June 2019 (contains modified Copernicus C3S information). Figure 1d: Temperature tercile summary predictions of multi-model ensemble model for June 2019 (contains modified Copernicus C3S information).

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 2019, above-normal temperature is favoured over most parts of Southeast Asia.

 

For JJA 2019, all three models – NCEP CFSv2, ECMWF, and UK Met Office (Figures 2 a-c) favour above-normal temperature over most parts of the region except south of the equator, where near-to-above normal temperature is predicted.

The models’ skill for temperature prediction is generally good for the JJA season for the above normal tercile (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office”).

Temperature tercile Summary of NCEP model.

Temperature tercile Summary of ECMWF model.

Figure 2a: Temperature tercile summary predictions of NCEP model for JJA 2019. Figure 2b: Temperature tercile summary predictions of ECMWF model for JJA 2019 (contains modified Copernicus C3S information).

Temperature tercile Summary of UK Met Office model.

Temperature tercile Summary of MME model.

Figure 2c: Temperature tercile summary predictions of UK Met Office model for JJA 2019 (contains modified Copernicus C3S information). Figure 2d: Temperature tercile summary predictions of multi-model ensemble model for JJA 2019 (contains modified Copernicus C3S information).

The qualitative outlook is assessed for the region in general, and based on the latest run from models provided by the SEA-RCC LRF node. 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.