Seasonal Forecast for September-October-November 2019

Updated 2 September 2019

Summary of Outlook

The Southwest Monsoon season typically persists until October, with the prevailing winds blowing from the southeast or southwest. During this period, the northern ASEAN region is in its rainy season, while dry conditions would prevail over the southern ASEAN region.

The Southwest Monsoon season transitions to inter-monsoon conditions by late-October or early-November. Inter-monsoon conditions are typically characterised by light and variable winds. These conditions also include an increase in shower activities over the southern ASEAN region.

For rainfall, below-normal conditions are expected over most parts of the Maritime Continent, particularly over southern Sumatra and Kalimantan, as well as the surrounding Java Sea areas. Above-normal rainfall is likely over some parts of the northern ASEAN region (southern parts of Myanmar and Thailand).

Above-normal temperature is expected over most parts of the ASEAN region during the Sep-Oct-Nov 2019 season except for regions south of the equator where near-normal or below-normal temperature is predicted, in particular over the oceans.

With drier-than-usual conditions forecast to persist over many parts of the southern ASEAN region, there may be further escalation of hotspot activities in the fire-prone provinces of Sumatra and Kalimantan. This could 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 September 2019, below-normal rainfall is favoured over most of equatorial and southern Southeast Asia. Elsewhere, predictions either are not consistent across models, or have low skill.

 

For September, 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 and southern Southeast Asia. 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. For those regions just north of the equator, the models generally only have 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 September 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 September 2019. Figure 1b: Rainfall tercile summary predictions of ECMWF model for September 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 September 2019 (contains modified Copernicus C3S information). Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for September 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 SON 2019, below-normal rainfall is favoured over most parts of the Maritime Continent. Some parts of northern Southeast Asia (southern parts of Myanmar and Thailand) are predicted to have increased chances of above-normal rainfall.

 

For SON 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, except for parts of the Philippines and northern Sumatra. The probability for below-normal category does vary between the models, with the ECMWF (Figure 2b) and NCEP (Figure 2a) models showing a higher probability of below-normal rainfall than the 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 and Thailand). Models’ skill scores for this region are also generally low for the SON 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 SON 2019. Figure 2b: Rainfall tercile summary predictions of ECMWF model for SON 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 SON 2019 (contains modified Copernicus C3S information). Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for SON 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 September 2019, above-normal temperature is favoured over most of the equatorial region. Elsewhere, temperatures are expected to be near-to-above normal for the northern ASEAN region, and below-to-near normal for the southern-most ASEAN region.

 

For September 2019, all three models – NCEP CFSv2, ECMWF, and UK Met Office (Figures 1a-c) – consistently predict above-normal temperature conditions for most of the equatorial region (including Sumatra, Peninsular Malaysia, Singapore, and Borneo). 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.

For the northern ASEAN region, all three models predict near-to-above normal temperatures. However, there are some differences for the band around 10°N, where the NCEP (Figure 1a) model is predicting near-normal temperature, compared to the ECMWF (Figure 1b) model that is predicting near-to above normal, and the UKMO (Figure 1c) model that is predicting above normal temperatures.

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 example, 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 September 2019. Figure 1b: Temperature tercile summary predictions of ECMWF model for September 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 September 2019 (contains modified Copernicus C3S information). Figure 1d: Temperature tercile summary predictions of multi-model ensemble model for September 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 SON 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 SON 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 SON 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 SON 2019. Figure 2b: Temperature tercile summary predictions of ECMWF model for SON 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 SON 2019 (contains modified Copernicus C3S information). Figure 2d: Temperature tercile summary predictions of multi-model ensemble model for SON 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.