Seasonal Forecast for August-September-October 2019

Updated 1 August 2019

Summary of Outlook

Climatologically, the prevailing Southwest Monsoon conditions are expected to persist till October 2019. The Southwest Monsoon season is characterised by rainy conditions over the northern ASEAN region and dry weather in the southern ASEAN region.

Above-normal temperatures are expected over most parts of the ASEAN region, except for the southernmost parts of the region where near-normal or below-normal temperatures are predicted, particularly over sea areas.

Below-normal rainfall is predicted over the southern ASEAN region and over southern Philippines, while wetter-than-normal conditions are expected in the southern parts of Cambodia, Myanmar, Thailand and Viet Nam.

Below-normal rainfall over the southern ASEAN may lead to an escalation of hotspot activities, particularly in the fire-prone areas in Sumatra and Kalimantan. This may lead to an increase in the risk of transboundary haze occurrence. In the northern ASEAN region, hotspot activities are expected to remain generally subdued due to rainy weather.

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

 

For August, 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 inland regions. The skill is generally highest south of the Equator where all three models tend to have moderate to high skill. North of the equator, however, the model 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, Cambodia and Viet Nam, where above-normal rainfall is predicted. Notwithstanding, model skill for August 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 August 2019. Figure 1b: Rainfall tercile summary predictions of ECMWF model for August 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 August 2019 (contains modified Copernicus C3S information). Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for August 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 ASO 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, Laos, and Vietnam) are predicted to have increased chances of above-normal rainfall.

 

For ASO 2019, all three models – NCEP CFSv2, ECMWF and the UK Met Office (Figures 2a-c) predict below-normal rainfall over for most parts of the Maritime Continent. The probability for below-normal category does vary between the models, with the ECMWF (Figure 2b) model showing a higher probability of below normal rainfall than the NCEP (Figure 2a) and UK Met Office (Figure 2c) models. 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, Laos, and Vietnam). Models’ skill scores for this region are also generally low for the ASO 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 ASO 2019. Figure 2b: Rainfall tercile summary predictions of ECMWF model for ASO 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 ASO 2019 (contains modified Copernicus C3S information). Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for ASO 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 August 2019, above-normal temperature is favoured over most areas around and north of the equator. South of the equator, below-to-near normal temperature is predicted, particularly over the ocean.

 

For August 2019, all three models – NCEP CFSv2, ECMWF, and UK Met Office (Figures 1a-c) – consistently predict above-normal temperature conditions over most areas near and north of the equator.

For southern 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 and northern Philippines (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 August 2019. Figure 1b: Temperature tercile summary predictions of ECMWF model for August 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 August 2019 (contains modified Copernicus C3S information). Figure 1d: Temperature tercile summary predictions of multi-model ensemble model for August 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 ASO 2019, above-normal temperature is favoured over most parts of Southeast Asia except for parts of the southern Maritime Continent where below-to-near normal temperature is predicted, particularly over the ocean.

 

For ASO 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 for the southern Maritime Continent, where below-to-near normal temperature is predicted, in particularly over the ocean.

The models’ skill for ASO 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 ASO 2019. Figure 2b: Temperature tercile summary predictions of ECMWF model for ASO 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 ASO 2019 (contains modified Copernicus C3S information). Figure 2d: Temperature tercile summary predictions of multi-model ensemble model for ASO 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.