Seasonal Forecast for March-April-May 2021
Updated 4 March 2021
Summary of Outlook
The prevailing Northeast Monsoon conditions are expected to continue into March 2021. During this period, the prevailing northeasterly or easterly winds over the northern ASEAN region could strengthen at times due to the influence of high pressure systems moving eastwards over continental Asia. In addition to the traditional dry season over the northern ASEAN region, areas in the equatorial parts of the southern ASEAN region could occasionally experience dry and windy conditions in March as they are in the dry phase of the Northeast Monsoon. Inter-monsoon conditions are expected to develop in April and continue into May 2021. The prevailing winds across the ASEAN region are expected to be light and variable and an increase in shower activities is forecast for the ASEAN region during this period.
For the March to May 2021 period, models predict above-normal rainfall over much of the ASEAN region north of the equator. La Niña conditions are present over the tropical Pacific Ocean, with climate models predicting La Niña conditions to weaken over the boreal spring (March – June). La Niña conditions are typically associated with wetter-than-normal conditions over the Southeast Asia region. While below-normal rainfall is expected for much of Sumatra, Borneo and Sulawesi for March – May, these areas tend to be less influenced by La Niña conditions at this time of year
Warmer-than-usual temperature is expected over the equatorial region for MAM 2021. Much of Mainland Southeast Asia, except Myanmar, may experience below- to near-normal temperatures.
Despite the slight chance of above-normal rainfall outlook over the Mekong sub-region in March-May 2021, dry conditions are expected to persist as it is still the traditional dry season for the Mekong sub-region. During this period, the hotspot situation and the risk of transboundary haze occurrence in the sub-region are likely to remain elevated. The gradual return of wet weather conditions from April 2021 onwards is expected to bring some respite to the elevated hotspot and haze situation over parts of the sub-region. In the southern ASEAN region, the hotspots activities are generally subdued during the outlook period. However, during periods of drier weather, there may be brief occurrences of isolated hotspots with localised smoke plumes, in particular over parts of the equatorial region where below-normal rainfall is forecast.
The qualitative outlook is assessed for the region in general and based on the latest runs from models provided by the SEA RCC-Network LRF node. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.
Monthly Rainfall Outlook – March 2021For March 2021, models predict above-normal rainfall over much of the ASEAN region just north of the equator, in particular southern Mainland Southeast Asia, Malay Peninsula and the Philippines.
For March 2021, above-normal rainfall is predicted over much of the ASEAN region between 0 and 15°N, as seen in the multi-model ensemble (Figure 4). The ECMWF (Figure 2) and the UK Met Office models (Figure 3) predict the above-normal rainfall to extend further northwest to central Myanmar and northern Lao PDR. The NCEP model (Figure 1) on the other hand predicts a larger extent of above-normal rainfall to the south of the equator covering southern Sumatra, southern Indonesia and Papua, where near- to below-normal rainfall is favoured by the other two models. Model skill for above normal tercile is moderate to high for the Malay Peninsula, northeast Borneo and the Philippines, and low for the other regions mentioned.
Elsewhere, there is either disagreement between the models or the skill is low for this time of the year.
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| Figure 1a: Rainfall tercile summary predictions of NCEP model for March 2021. | Figure 1b: Rainfall tercile summary predictions of ECMWF model for March 2021 (contains modified Copernicus C3S information). |
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| Figure 1c: Rainfall tercile summary predictions of UK Met Office model for March 2021 (contains modified Copernicus C3S information). | Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for March 2021 (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 – March-April-May 2021 (MAM 2021)For MAM 2021, there is an increased chance of above-normal rainfall for most of the ASEAN region north of the equator, and below-normal rainfall for much of Sumatra, Borneo and Sulawesi.
For MAM 2021, all three models – NCEP, ECMWF, and UK Met Office (Figures 1-3) – are in agreement of an increased chance of above-normal rainfall for much of the ASEAN region north of the equator, except for northern Myanmar where there is disagreement between the models. The model skill for the above-normal tercile is moderate to good for the band around 10°N, which includes much of the region where above-normal rainfall is predicted except for northern Mainland Southeast Asia, where the model skill is low to moderate.
South of the equator, the three models are also in agreement with below- to near-normal rainfall for southern Sumatra, western Borneo, and Sulawesi. Near- to above-normal rainfall is also predicted for southern Indonesia. However, the model skill is only low to moderate for these regions.
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| Figure 2a: Rainfall tercile summary predictions of NCEP model for MAM2021. | Figure 2b: Rainfall tercile summary predictions of ECMWF model for MAM2021 (contains modified Copernicus C3S information). |
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| Figure 2c: Rainfall tercile summary predictions of UK Met Office model for MAM 2021 (contains modified Copernicus C3S information). | Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for MAM 2021 (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 – March 2021For March 2021, above-normal temperature is favoured over much of the Maritime Continent and Myanmar.
For March 2021, an increased chance of above-normal temperature is predicted over much of the Maritime Continent (apart from the Malay Peninsula) and also Myanmar, as seen in the multi-model ensemble (Figure 4). The area with the highest likelihood for the above-normal temperature varies among the three models, with the NCEP model (Figure 1) predicting so over the entire mentioned region, the ECMWF model (Figure 2) favouring region around the Philippines, and the UK Met Office model (Figure 3) favouring southeast Maritime Continent. Models’ skill for above-normal tercile for the Maritime Continent is moderate to high with lower model skill for the Philippines and Sumatra regions, while model skill is low to moderate for Myanmar.
For the Malay Peninsula, near- to above-normal temperature is predicted, with the NCEP model going for above-normal, the UK Met Office model for near-normal and ECMWF model predicting a mix between the two. Model skill is low to moderate for the region mentioned.
For Mainland Southeast Asia apart from Myanmar, there is disagreement between the models. The NCEP model (Figure 1) predicts increased chance of above-normal temperature, the UK Met Office model (Figure 3) predicts below-normal temperature, and ECMWF model (Figure 2) predicts no dominant tercile for the region. Model skill is low to moderate for much of the Mainland Southeast Asia.
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| Figure 3a: Temperature tercile summary predictions of NCEP model for March 2021. | Figure 3b: Temperature tercile summary predictions of ECMWF model for March 2021 (contains modified Copernicus C3S information). |
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| Figure 3c: Temperature tercile summary predictions of UK Met Office model for March 2021 (contains modified Copernicus C3S information). | Figure 3d: Temperature tercile summary predictions of multi-model ensemble model for March 2021 (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 – March-April-May 2021 (MAM 2021)For MAM 2021, an increased chance of above-normal temperature is predicted over the equatorial region, while below- to near-normal temperatures are favoured over much of eastern Mainland Southeast Asia.
For MAM 2021, all three models – NCEP, ECMWF and UK Met Office (Figures 1-3) – predict an increased chance of above-normal temperature for much of the equatorial region, in particular Sumatra, Borneo, Sulawesi and Papua. Near-normal temperature is predicted for the Malay Peninsula as seen in the multi-model ensemble (Figure 4). Elsewhere in the Maritime Continent, the model’s predictions are mixed. For Java, the NCEP model (Figure 1) is predicting a high likelihood of above-normal temperature, while the ECMWF (Figure 2) and UK Met Office (Figure 3) models are predicting near- to above-normal temperature. For the Philippines, the NCEP and ECMWF models predict above-normal temperature, while the UK Met Office model predicts near normal temperature. The model skill for the above-normal tercile for the Maritime Continent is moderate to good.
For central and eastern Mainland Southeast Asia, below- to near-normal temperatures are predicted by the three models as seen in the multi-model ensemble (Figure 4). In particular, the UK Met Office model is predicting a higher chance of below-normal temperature for much of eastern Mainland Southeast Asia, while the NCEP and the ECMWF models are predicting mostly near-normal temperature. For Myanmar, the NCEP and the UK Met Office models are predicting above-normal temperature, while the ECMWF model is predicting below- to near-normal temperature. The model skill is low to moderate for Mainland Southeast Asia.
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| Figure 4a: Temperature tercile summary predictions of NCEP model for MAM 2021. | Figure 4b: Temperature tercile summary predictions of ECMWF model for MAM 2021 (contains modified Copernicus C3S information). |
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| Figure 4c: Temperature tercile summary predictions of UK Met Office model for MAM 2021 (contains modified Copernicus C3S information). | Figure 4d: Temperature tercile summary predictions of multi-model ensemble model for MAM 2021 (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 skillfulness 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.