Seasonal Forecast for July-August-September 2019

Updated 2 July 2019

Summary of Outlook

The prevailing Southwest Monsoon conditions are expected to continue until October 2019, with winds over the region blowing mainly from the southeast or southwest. Climatologically, the Southwest Monsoon season is characterised by rainy conditions in the northern ASEAN region and dry conditions in the southern ASEAN region.

Above-normal temperatures are likely over most parts of Southeast Asia during the Jul-Aug-Sep 2019 season except for parts of the southern ASEAN region where there may be near-normal or below-normal temperatures, in particular over sea areas.

Below-normal rainfall is likely over most parts of the southern ASEAN region, but some parts of northern ASEAN region may receive above-normal rainfall (viz southern parts of Myanmar, Thailand, Cambodia, and Vietnam).

In the northern ASEAN region, hotspot activities are expected to remain subdued due to the rainy weather. In the southern ASEAN region, the expected dry weather could contribute to an increase in hotspot activities, particularly over the fire-prone provinces of Sumatra and Kalimantan. This may lead to a corresponding increase in the risk of transboundary haze occurrence.

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 July 2019, below-normal rainfall is favoured over most of equatorial Southeast Asia spanning from 10°S to 7°N. Elsewhere, predictions either are not consistent across models, or have low skill.

 

For July’s rainfall, all three models – NCEP CFSv2, ECMWF and the UK Met Office (Figures 1a-c) – predict an increased chance of below-normal rainfall for most parts of equatorial Southeast Asia (from 10°S to 7°N). The higher probabilities of below-normal rainfall are over regions south of the Equator where all three models tend to have moderate to high skill. North of the equator, however, the models are less confident of below-normal rainfall, and it corresponds to regions where there are only low to moderate skill.

For northern Southeast Asia, the three models differ in their predictions, except for coastal areas of the southern parts of Myanmar, Thailand and Viet Nam, as well as over Cambodia where above-normal rainfall is predicted. Notwithstanding, model skill for July over land in this part of the region is generally poor (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 July 2019. Figure 1b: Rainfall tercile summary predictions of ECMWF model for July 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 July 2019 (contains modified Copernicus C3S information). Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for July 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 JAS 2019, below-normal rainfall is favoured over most parts of the Maritime Continent. Some parts of northern Southeast Asia (southern parts of Myanmar, Thailand, Cambodia, and Vietnam) are predicted to have increased chances of above-normal rainfall.

 

For JAS 2019, all three models – NCEP CFSv2, ECMWF and the UK Met Office (Figures 2a-c) predict below-normal rainfall over most parts of Maritime Continent. The spatial extent of the affected areas and the likelihood for below-normal category is consistent across the different models, but it may reflect the models’ tendencies to over-predict effect of El Niño which is still uncertain. Overall, the models’ skill scores for rainfall are relatively good over the Maritime Continent except for northern parts of Borneo, and Sumatra, as well as Peninsular Malaysia.

There is no consistent prediction for much of northern Southeast Asia, although there is increased likelihood for above-normal rainfall for select regions (e.g. southern coastal parts of Myanmar, Thailand, Cambodia, and Vietnam). Models’ skill scores for this region are also generally low for the JAS season (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 2a: Rainfall tercile summary predictions of NCEP model for JAS 2019. Figure 2b: Rainfall tercile summary predictions of ECMWF model for JAS 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 JAS 2019 (contains modified Copernicus C3S information). Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for JAS 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 July 2019, above-normal temperature is favoured over most areas north of the equator. Elsewhere in eastern Maritime Continent, below-to-near normal temperature is predicted, in particular over the ocean.

 

For July 2019, all three models – NCEP CFSv2, ECMWF, and UK Met Office (Figures 1a-c) – consistently predict above-normal temperature conditions over most areas north of the equator. The NCEP CFSv2 however predicts a considerable chance of below-normal temperature conditions over land regions between 10°N – 20°N.

For southern and eastern parts of the Maritime Continent, in particular over the ocean, all three models predict below-to-near normal temperature conditions with different likelihoods.

The models’ skill scores for predicting both above- and below-normal temperature terciles are generally good over most parts of Southeast Asia except for some parts of the region, for e.g. northern Borneo (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 July 2019. Figure 1b: Temperature tercile summary predictions of ECMWF model for July 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 July 2019 (contains modified Copernicus C3S information). Figure 1d: Temperature tercile summary predictions of multi-model ensemble model for July 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 JAS 2019, above-normal temperature is favoured over most parts of Southeast Asia except for parts of the eastern and southern Maritime Continent where below-to-near normal temperature is predicted, in particular over the ocean.

 

For JAS 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 below-to-near normal temperature is predicted, in particularly over the ocean.

The models’ skill for JAS temperature prediction is generally good, for both below-normal and above-normal terciles (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 JAS 2019. Figure 2b: Temperature tercile summary predictions of ECMWF model for JAS 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 JAS 2019 (contains modified Copernicus C3S information). Figure 2d: Temperature tercile summary predictions of multi-model ensemble model for JAS 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.