Seasonal Forecast for December-January-February 2021-2022
Updated 1 December 2021
The Southwest Monsoon had transitioned into the inter-monsoon period from the second half of October 2021. Climatologically, inter-monsoon conditions are likely to prevail over the ASEAN region in November before Northeast Monsoon conditions develop in December. During the inter-monsoon period, the prevailing winds are forecast to be generally light and variable in direction. With the monsoon rain band located close to the equator, an increase in rainfall over the equatorial ASEAN region can also be expected.
For the December 2021 to February 2022 period, there is an increased chance of near- to above-normal rainfall over much of the Maritime Continent, and a mix of below- to above-normal rainfall over Mainland Southeast Asia. La Niña conditions are present. Models are predicting weak to moderate La Niña conditions until March-April, after which the conditions are predicted to weaken. The negative IOD event has ended and is expected to be neutral for the coming months. Warmer-than-usual temperature is expected for much of the Maritime Continent and Myanmar during DJF 2021-2022.
The dry season over the southern ASEAN region had ended in mid-October 2021 and the overall hotspot activity in the region is likely to remain subdued till the end of 2021. Persistent dry conditions which typically occur during the dry phase of the Northeast Monsoon from late January to February are likely to contribute to an increase in hotspot activity in parts of the southern ASEAN region and increase the risk of smoke plumes development. In the northern ASEAN region, the traditional dry season typically sets in at the end of the year. While there is an increased chance of above-normal rainfall over some parts of the northern ASEAN region, hotspot and smoke haze activity can still be expected to progressively intensify over the fire-prone areas in the Mekong sub-region, with an increased likelihood of transboundary haze occurrence during this period.
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 – December 2021For December 2021, there is an increase in chance of above-normal rainfall over the eastern Maritime Continent and southeastern Mainland Southeast Asia.
For December 2021, based on the multi-model ensemble (Figure 4), there is an increase in chance of above-normal rainfall over the eastern Maritime Continent. The highest likelihood of above-normal rainfall is over the Philippines for all three models (Figures 1 to 3). The models predict below- to near-normal rainfall over the central and western Maritime Continent with the NCEP model predicting the highest probability of below-normal rainfall. However, the model’s skill is only low to moderate for this region. Over the eastern Maritime Continent, the models’ skill is moderate to relatively high for eastern parts of the region.
For Mainland Southeast Asia, based on the multi-model ensemble (Figure 4), there is an increase in chance of above-normal rainfall over the southeastern region and below-normal rainfall over the northeastern region. Elsewhere, there is either no dominant tercile predicted or disagreement between the models. The models’ skill is generally low to moderate for Mainland Southeast Asia, with moderate skill over southeastern parts.
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| Figure 1a: Rainfall tercile summary predictions of NCEP model for December 2021. | Figure 1b: Rainfall tercile summary predictions of ECMWF model for December 2021 (contains modified Copernicus C3S information). |
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| Figure 1c: Rainfall tercile summary predictions of UK Met Office model for December 2021 (contains modified Copernicus C3S information). | Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for December 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 – December-January-February 2021-2022 (DJF 2021-2022)For DJF 2021-2022, there is an increased chance of near- to above-normal rainfall over much of the Maritime Continent, and a mix of below- to above-normal rainfall over Mainland Southeast Asia
For DJF 2021-2022, based on the multi-model ensemble (Figure 4), there is an increased chance of near- to above-normal rainfall for much of the Maritime Continent, except for some parts of the equatorial region where below- to near-normal rainfall or no dominant tercile is predicted. The highest likelihood of above-normal rainfall is over northeast parts of the Maritime Continent. NCEP model (Figure 1) is most confident of below-normal rainfall over Borneo, while UK Met Office and ECMWF models (Figures 2 and 3) predict a smaller increase in chance of below-normal rainfall. The models’ skill is moderate to relatively high for northeastern parts of the Maritime Continent and low to moderate elsewhere.
For Mainland Southeast Asia, based on the multi-model ensemble (Figure 4), there is an increase in chance of above-normal rainfall for the southeastern region, and below-normal rainfall for parts of northern Mainland Southeast Asia. Among the models, NCEP model is most confident for below-normal rainfall, while UKMO and ECMWF models predict a smaller increase in chance of below-normal rainfall. However, model skill is low for this season for Mainland Southeast Asia.
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| Figure 2a: Rainfall tercile summary predictions of NCEP model for DJF 2021-2022. | Figure 2b: Rainfall tercile summary predictions of ECMWF model for DJF 2021-2022 (contains modified Copernicus C3S information). |
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| Figure 2c: Rainfall tercile summary predictions of UK Met Office model for DJF 2021-2022 (contains modified Copernicus C3S information). | Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for DJF 2021-2022 (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 – December 2021For December 2021, an increased chance of above-normal temperature is predicted over much of the Maritime Continent.
For December 2021, all three models – NCEP, ECMWF and UK Met Office (Figures 1-3) – predict above-normal temperature over much of the Maritime Continent, except over Java where near-normal temperature is predicted. The highest likelihood for above-normal temperatures is over the eastern Maritime Continent (Figure 4).
For Mainland Southeast Asia, based on the multi-model ensemble (Figure 4), above-normal temperature is predicted over Myanmar and below- to near-normal temperature is predicted over northeast Mainland Southeast Asia. Elsewhere, there is ether no dominant tercile or disagreement between the three models (Figures 1-3).
The models’ skill for predicting below- and above-normal temperature is moderate to relatively high across Southeast Asia, except for the northern parts of the region where the skill is low to moderate.
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| Figure 3a: Temperature tercile summary predictions of NCEP model for December 2021. | Figure 3b: Temperature tercile summary predictions of ECMWF model for December 2021 (contains modified Copernicus C3S information). |
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| Figure 3c: Temperature tercile summary predictions of UK Met Office model for December 2021 (contains modified Copernicus C3S information). | Figure 3d: Temperature tercile summary predictions of multi-model ensemble model for December 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 – December-January-February 2021-2022 (DJF 2021-2022)For DJF 2021-2022, an increased chance of above-normal temperature is predicted over much of the Maritime Continent and Myanmar.
For DJF 2021-2022, all three models – NCEP, ECMWF and UK Met Office (Figures 1-3) – predict above-normal temperature over much of the Maritime Continent. The highest likelihood for above-normal temperatures is over the eastern Maritime Continent (Figure 4).
For Mainland Southeast Asia, the three models (Figures 1-3) predicted a mix of below- to above-normal temperatures. While all three models predict above-normal temperature over Myanmar, there is either no dominant tercile predicted or disagreement between the models elsewhere.
The seasonal models’ skill is relatively high for the Maritime Continent. For Mainland Southeast Asia, models’ skill is moderate to relatively high for below- and above-normal and low to moderate for near-normal.
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| Figure 4a: Temperature tercile summary predictions of NCEP model for DJF 2021-2022. | Figure 4b: Temperature tercile summary predictions of ECMWF model for DJF 2021-2022 (contains modified Copernicus C3S information). |
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| Figure 4c: Temperature tercile summary predictions of UK Met Office model for DJF 2021-2022 (contains modified Copernicus C3S information). | Figure 4d: Temperature tercile summary predictions of multi-model ensemble model for DJF 2021-2022 (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.