Seasonal Forecast for May-June-July 2020
Updated 28 April 2020
Summary of Outlook
Inter-monsoon conditions over the ASEAN region typically span between March and May, before a gradual transition to the Southwest Monsoon season around late-May/June. The transition is characterised by a northward shift of the monsoon rain band, leading to increased shower activities over the northern ASEAN region. Climatologically, the Southwest Monsoon season is associated with the traditional wet season for the northern ASEAN region, and the traditional dry season for the southern ASEAN region.
For May to July 2020, the rainfall over the northern ASEAN region is forecast to be below-normal, while above-normal rainfall is expected over most parts of the southern ASEAN region. Above-normal temperatures are expected to continue over the ASEAN region for the next three months.
In the Mekong sub-region, the expected increase in shower activities in May 2020 associated with the start of the Southwest Monsoon is likely to bring a further improvement to the haze situation. The showers will also help to gradually subdue the hotspot and fire activities in the sub-region.
In the southern ASEAN region, the hotspot activities are expected to remain generally subdued in May 2020. However, a gradual increase in hotspot activities, particularly in the fire-prone areas of Sumatra and Kalimantan, can be expected from June with the onset of the traditional dry season in the southern ASEAN region.
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.
Monthly Rainfall Outlook – May 2020For May 2020, below-normal rainfall is predicted for much of northern Southeast Asia, while above-normal rainfall is predicted for the southern half of Southeast Asia.
For May 2020, all three models – NCEP CFSv2, ECMWF, and UK Met Office – predict an increased chance of below-normal rainfall for most parts of Southeast Asia north of 10°N (Figures 1a-c). However, one of the three models – NCEP CFSv2 (Figure 1a) – predicts a lower probability of drier conditions over southern Mainland Southeast Asia and the Philippines. Model skill for the Southeast Asia north of 10°N is moderate to relatively high.
In the southern half of Southeast Asia, all three models predict an increased chance of above-normal rainfall for much of the region, with the ECMWF and UK Met Office models predicting the highest likelihood. The corresponding skill scores are low to moderate for this region, although the ECMWF model has slightly higher skill for this region at this time of year (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office”).
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| Figure 1a: Rainfall tercile summary predictions of NCEP model for May 2020. | Figure 1b: Rainfall tercile summary predictions of ECMWF model for May 2020 (contains modified Copernicus C3S information). |
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| Figure 1c: Rainfall tercile summary predictions of UK Met Office model for May 2020 (contains modified Copernicus C3S information). | Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for May 2020 (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.
Seasonal Rainfall Outlook – May-June-July 2020 (MJJ 2020)For MJJ 2020, above-normal rainfall is predicted for much of the southern half of Southeast Asia, with a slight increase in chance of below-normal rainfall for western Mainland Southeast Asia.
For MJJ 2020, all three models – NCEP CFSv2, ECMWF, and UK Met Office (Figures 2a-c) – predict an increased chance of above-normal rainfall over southern Southeast Asia, but models again differ in the spatial extent and intensity of the wetter conditions. The skill is moderate to high for most of this region, apart from over northern Sumatra.
Below-normal rainfall conditions are predicted by all three models for most parts of western Mainland Southeast Asia (Myanmar, northern Thailand and northern Laos). However, the skill is low to moderate for this region. Elsewhere, the models show inconsistent forecasts or have limited skill (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office“).
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| Figure 2a: Rainfall tercile summary predictions of NCEP model for MJJ 2020. | Figure 2b: Rainfall tercile summary predictions of ECMWF model for MJJ 2020 (contains modified Copernicus C3S information). |
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| Figure 2c: Rainfall tercile summary predictions of UK Met Office model for MJJ 2020 (contains modified Copernicus C3S information). | Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for MJJ 2020 (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.
Monthly Temperature Outlook – May 2020For May 2020, above-normal temperature is favoured over most parts of Southeast Asia.
For May 2020, all three models – NCEP CFSv2, ECMWF and UK Met Office (Figures 1a-c) –predict a high likelihood of above-normal temperature conditions over most parts of Southeast Asia.
The models’ skill scores for predicting above-normal temperature is generally good across Southeast Asia, except for parts of northern Mainland Southeast Asia where the skill is only low to moderate (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office”).
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| Figure 1a: Temperature tercile summary predictions of NCEP model for May 2020. | Figure 1b: Temperature tercile summary predictions of ECMWF model for May 2020 (contains modified Copernicus C3S information). |
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| Figure 1c: Temperature tercile summary predictions of UK Met Office model for May 2020 (contains modified Copernicus C3S information). | Figure 1d: Temperature tercile summary predictions of multi-model ensemble model for May 2020 (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.
Seasonal Temperature Outlook – May-June-July (MJJ 2020)For MJJ 2020, above-normal temperature is favoured over most parts of Southeast Asia.
For MJJ 2020, all three models – NCEP CFSv2, ECMWF and UK Met Office (Figures 2 a-c) – favour above-normal temperature conditions over most parts of Southeast Asia. The models’ skill for this season is moderate to high for much of Southeast Asia (see the respective sections of “Model products and verification: NCEP, ECMWF, UK Met Office”).
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| Figure 2a: Temperature tercile summary predictions of NCEP model for MJJ 2020. | Figure 2b: Temperature tercile summary predictions of ECMWF model for MJJ 2020 (contains modified Copernicus C3S information). |
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| Figure 2c: Temperature tercile summary predictions of UK Met Office model for MJJ 2020 (contains modified Copernicus C3S information). | Figure 2d: Temperature tercile summary predictions of multi-model ensemble model for MJJ 2020 (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.
Frequently Asked Questions
What is a seasonal forecast?
A seasonal forecast provides forecast information about the general weather conditions at seasonal timescales up to several months ahead. Long range predictions rely on predicting components of the atmosphere and the oceans which show variations at large spatial and temporal scales. Among these key components is the sea-surface temperature – an important indicator in the El Niño Southern Oscillation (ENSO) cycle.
Example of probabilistic long range forecast using the multi-model ensemble. For areas nearby Peninsular Malaysia, the forecast is showing a probability of 50-70% of rainfall being in the below-normal (33%) tercile range. (Source: WMO LC LRF)
To account for the chaotic nature of the atmosphere, seasonal forecast adopts a probabilistic approach and the forecast weather condition is presented as an average over an extended period of time, usually with reference to climatology.
ASMC carries out monthly seasonal forecast predictions based on various seasonal model forecasts from the leading meteorological centres, supplemented by individual assessments from respective countries in South East Asia. The skilfulness of seasonal forecast relies greatly on the performance of seasonal models, which differ from one place to another and for different seasons of the year.
Receiver operating characteristic (ROC) score of UK GloSea5 seasonal hindcast for above-normal precipitation scenario for Dec – Feb (left) and May – Jul (right) over Asia region. Higher ROC score (indicated in red) means better model skill. (Source: UK Met Office)
For example, one way to assess the seasonal model skills is to examine the ROC score. From the figures above, we can see that ROC score map differs greatly from one season to another. During the period from Dec to Feb, a high ROC score region is observed mainly over the Philippines whereas during the period from May to Jul, a high ROC score region is observed over the near equatorial region such as Peninsular Malaysia and Sumatra.