Seasonal Forecast for December 2024 – February 2025
Updated 4 December 2024
In December, the inter-monsoon conditions typically transition to the Northeast Monsoon over the ASEAN region. During this period, the prevailing winds over the ASEAN region are expected to strengthen and blow from the northwest or northeast as the monsoon rain band shifts towards the south of the Equator.
For the December 2024 to February 2025 (DJF) period, models predict an increased chance of above-normal rainfall over much of the Maritime Continent, and below-normal rainfall over the western equatorial region. There are signs of La Niña-like conditions, with a weak and short-lived La Niña likely to develop sometime in December 2024 and persist until February 2025. While there were signs of a negative Indian Ocean Dipole (IOD) in October, these conditions are predicted to be short lived, with the IOD index predicted to return to neutral by December 2024. Above-normal temperature is predicted over much of the ASEAN region for DJF 2024-2025.
During the DJF period, the overall hotspot and smoke haze situation for the southern ASEAN region is likely to remain subdued under generally wet weather conditions, while the dry season for the northern ASEAN region is expected to begin in December. Although above-normal rainfall is forecasted for much of the Mekong sub-region, increased hotspots and smoke haze are likely to develop in fire-prone areas during the review period. Isolated hotspots and smoke plumes may also form in parts of the southern ASEAN region experiencing occasional drier periods, particularly during the dry phase of the Northeast Monsoon typically in late January and February.
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.
For December 2024, above-normal rainfall is predicted over most of the Maritime Continent except over parts of Borneo and Sumatra.
For December 2024, above-normal rainfall is predicted over the northern and southern Maritime Continent, and below-normal rainfall is predicted over parts of the central equatorial region based on the multi-model ensemble (Figure 4). The NCEP and UK Met Office models (Figures 1 and 3) show higher confidence for below-normal rainfall over Sumatra and Borneo, followed by the ECMWF model (Figure 2) with below-normal rainfall predicted for Sumatra and near-normal rainfall over Borneo. In contrast, the ECMWF model has higher confidence for the above-normal rainfall for much of the rest of the Maritime Continent, followed by the UK Met Office and NCEP models. Models’ skill is moderate to good for both above- and below-normal rainfall over the Maritime Continent, except over the Malay Peninsula where model skill is low.
Above-normal rainfall is predicted over most of Mainland Southeast Asia based on the multi-model ensemble (Figure 4) except the northeastern region. However, it is the dry season for Mainland Southeast Asia. The NCEP model (Figure 1) has the largest extent and confidence of above-normal rainfall, followed by the ECMWF model (Figure 2) and the UK Met Office model (Figure 3). Models’ skill for above-normal rainfall is generally low for the mentioned regions.
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| Figure 1: Rainfall tercile summary predictions of NCEP model for December 2024 (contains modified Copernicus C3S information). | Figure 2: Rainfall tercile summary predictions of ECMWF model for December 2024 (contains modified Copernicus C3S information). |
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| Figure 3: Rainfall tercile summary predictions of UK Met Office model for December 2024 (contains modified Copernicus C3S information). | Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for December 2024 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological rainfall’s lower tercile boundary for December based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for December based on CHIRPS (reference period: 1991-2020). |
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 DJF 2024/2025, models predict an increased chance of above-normal rainfall over much of the Maritime Continent, and below-normal rainfall over the western equatorial region.
For DJF 2024/2025, above-normal rainfall is predicted over much of the Maritime Continent, based on the multi-model ensemble (Figure 4) except over the western equatorial region where below-normal rainfall is predicted. The ECMWF model (Figure 2) shows the highest confidence for above-normal rainfall over the region, followed by the UK Met Office model (Figure 3) and then the NCEP model (Figure 1). Models’ skill is low to moderate for both below-normal and above-normal rainfall for much of the Maritime Continent, except for over the Philippines where the models’ skill is relatively good.
For Mainland Southeast Asia, all three models (Figures 1 – 3) agree on above-normal rainfall over the southeastern region and a mix of near- to above-normal or no dominant tercile elsewhere. However, it is the dry season for the region and the models’ skill is generally low.
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| Figure 1: Rainfall tercile summary predictions of NCEP model for DJF 2024-2025 (contains modified Copernicus C3S information). | Figure 2: Rainfall tercile summary predictions of ECMWF model for DJF 2024-2025 (contains modified Copernicus C3S information). |
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| Figure 3: Rainfall tercile summary predictions of UK Met Office model for DJF 2024-2025 (contains modified Copernicus C3S information). | Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for DJF 2024-2025 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological rainfall’s lower tercile boundary for DJF based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for DJF based on CHIRPS (reference period: 1991-2020). |
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 December 2024, above-normal temperature is predicted over much of the ASEAN region.
For December 2024, above-normal temperature is predicted over much of the ASEAN region. For the Maritime Continent, above-normal temperature is predicted based on the multi-model ensemble (Figure 4). All three models agree on above-normal temperature over the Maritime Continent, especially for the ECMWF and UK Met Office models (Figures 2 and 3) predicting with high confidence over most of the region and followed by the NCEP model (Figure 1) predicting with high confidence over the equatorial region.
For Mainland Southeast Asia, near-normal temperature is predicted for the eastern region with above-normal temperature predicted elsewhere, based on the multi-model ensemble. The NCEP model (Figure 1) predicts below-normal temperature over northeastern parts of Mainland Southeast Asia with the largest extent of near-normal temperature over central and eastern Mainland Southeast Asia, followed by the ECMWF model with near-normal temperature predicted over the southeastern region, then the UK Met Office model for the northeastern region. Models’ skill is moderate to good for predicting below- and above-normal temperature over most of the ASEAN region, except northwestern Mainland Southeast Asia with low models’ skill.
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| Figure 1: Temperature tercile summary predictions of NCEP model for December 2024 (contains modified Copernicus C3S information). | Figure 2: Temperature tercile summary predictions of ECMWF model for December 2024 (contains modified Copernicus C3S information). |
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| Figure 3: Temperature tercile summary predictions of UK Met Office model for December 2024 (contains modified Copernicus C3S information). | Figure 4: Temperature tercile summary predictions of multi-model ensemble model for December 2024 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological temperature for December based on ERA5 (reference period: 1991-2020). |
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 DJF 2024/2025, the models predict an increased chance of above-normal temperature over much of the ASEAN region.
For DJF 2024/2025, above-normal temperature is predicted for much of the ASEAN region, except for parts of the eastern Mainland Southeast Asia where near-normal temperature is predicted, based on the multi-model ensemble (Figure 4). All three models agree with high confidence on above-normal temperature over most of the southern and northwestern ASEAN region. Models’ skill for predicting above-normal and near-to-above-normal temperature for the ASEAN region is relatively good for much of the region, apart from western half of Mainland Southeast Asia with low to moderate model skill.
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| Figure 1: Temperature tercile summary predictions of NCEP model for DJF 2024-2025 (contains modified Copernicus C3S information). | Figure 2: Temperature tercile summary predictions of ECMWF model for DJF 2024-2025 (contains modified Copernicus C3S information). |
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| Figure 3: Temperature tercile summary predictions of UK Met Office model for DJF 2024-2025 (contains modified Copernicus C3S information). | Figure 4: Temperature tercile summary predictions of multi-model ensemble model for DJF 2024-2025 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological temperature for DJF based on ERA5 (reference period: 1991-2020). |
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.