Seasonal Forecast for November, December, January 2018/2019

Updated 5 November 2018

Summary of Outlook

The prevailing inter-monsoon conditions are expected to transition into the Northeast Monsoon season in late November/early December 2018. During the NDJ season, the monsoon rain band is forecast to gradually shift south towards the Equator. For the southern ASEAN region, the shift in the rain band is forecast to bring an increase in shower activities and winds that are light and variable in direction. In contrast, a decrease in shower activities and a gradual strengthening of northeasterly winds can be expected for the northern ASEAN region.

During this season, based on numerical prediction models, many parts of the ASEAN region especially over the equatorial region can expected above-normal temperatures while elsewhere, climatological probabilities are predicted.

While near-normal or below-normal rainfall is predicted over the Philippines and the region surrounding the Java sea, there is some agreement among the models of an increased chance of above-normal rainfall over parts of northern Sumatra, Peninsular Malaysia and Borneo. In other areas, climatological probabilities are predicted.

With the onset of the traditional dry season over the northern ASEAN region in December 2018, extended periods of drier weather could lead to an increase in hotspot activities.

In contrast, rainy conditions over the southern ASEAN region are likely to keep hotspot activities generally subdued. However, there could still be isolated hotspots during occasional brief periods of dry 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 November 2018, below-normal is favoured over much of southern ASEAN region and the Philippines. Elsewhere, climatological probabilities are predicted.

 
For November’s rainfall, all three models – NCEP CFSv2, ECMWF, and the UK Met Office (Figures 1a-c) predict below-normal conditions for much the southern ASEAN region and the Philippines. NCEP CFSv2 predicts the largest spatial extent of below-normal conditions, including most of Borneo and parts of Peninsular Malaysia, while ECMWF and the UK Met Office restrict the drier conditions to the Philippines and those regions south of the equator.

For the rest of the northern ASEAN region, there is no dominant tercile among the models, indicating climatological probabilities, apart from northern Myanmar. Here, all three models predict an increase likelihood of below-normal rainfall, although the skill is low for this region in all models.

Overall, the models’ skill for rainfall are very good south of the equator, the Philippines, and parts of the South China Sea (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office”).

Rainfall Tercile Summary of NCEP model.

Figure 1a: Rainfall tercile summary predictions of NCEP model for November 2018.

Rainfall Tercile Summary of ECMWF model.

Rainfall Tercile Summary of Met Office model.

Figure 1b: Rainfall tercile summary predictions of ECMWF model for November 2018 (contains modified Copernicus C3S information). Figure 1c: Rainfall tercile summary predictions of UK Met Office model for November 2018 (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 NDJ 2018/2019, below-normal or near-normal rainfall is favoured over much of the Maritime Continent. There is some agreement among the models of an increased chance of above-normal rainfall over the western equatorial region.

 
For NDJ 2018/2019, all three models – NCEP CFSv2, ECMWF, and UK Met Office (Figures 2a-c) predict below-normal over the Philippines and below- to near-normal rainfall in the region surrounding the Java Sea and eastern Indonesia. All three models have generally good skill (NCEP, ECMWF, UK Met Office) over these regions.

The models predict to various degrees an increased probability of above-normal rainfall over the western equatorial region (parts of northern Sumatra, Peninsular Malaysia and Borneo). However, the models do not predict an increased chance of way above normal rainfall (highest 20%), and model skill for this region is only low to moderate.

For the rest of the northern ASEAN region, there is little agreement between the NCEP CFSv2, ECMWF and UK Met Office models, with the skill generally low for this region during NDJ.

Rainfall Tercile Summary of NCEP model.

Figure 2a: Rainfall tercile summary predictions of NCEP model for NDJ 2018-2019.

Rainfall anomaly of ECMWF model.

Rainfall Tercile Summary of Met Office model.

Figure 2b: Rainfall tercile summary predictions of ECMWF model for NDJ 2018-2019 (contains modified Copernicus C3S information). Figure 2c: Rainfall tercile summary predictions of UK Met Office model for NDJ 2018-2019 (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 November 2018, above-normal temperature is favoured over many parts of Southeast Asia.

 
All three models – NCEP CFSv2, ECMWF, and UK Met Office (Figures 1a-c) provide a consistent outlook for above-normal temperature over most parts of the ASEAN region, except for northern Myanmar and the Philippines. There is no dominant tercile for northern Myanmar based on the ECMWF and UK Met Office models, while the three models disagree about the dominant tercile for the Philippines. The magnitude of the likelihood for above-normal temperature is higher for NCEP CFSv2 than the ECMWF and the UK Met Office models, consistent with previous months’ outlooks.

Over land across the region, the models’ skill for temperature prediction are 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 November 2018. Figure 1b: Temperature tercile summary predictions of ECMWF model for November 2018 (contains modified Copernicus C3S information).

Temperature Tercile Summary of Met Office model.

Figure 1c: Temperature tercile summary predictions of UK Met Office model for November 2018 (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 NDJ 2018/2019, above-normal temperature is favoured over most of Southeast Asia.

 
For the NDJ 2018/19, all three models – NCEP CFSv2, ECMWF, and UK Met Office (Figures 2 a-c) favour above-normal temperature conditions over most the region with the highest likelihood over the equatorial region.

Over land across the region, the models’ skill for temperature prediction are generally very good (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office”).

Temperature Tercile Summary of NCEP model.

Figure 2a: Temperature tercile summary predictions of NCEP model for NDJ 2018-2019.

Temperature Tercile Summary of ECMWF model.

Temperature Tercile Summary of Met Office model.

Figure 2b: Temperature tercile summary predictions of ECMWF model for NDJ 2018-2019 (contains modified Copernicus C3S information). Figure 2c: Temperature tercile summary predictions of UK Met Office model for NDJ 2018-2019 (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.