Seasonal Forecast for March – May 2023
Updated 2 March 2023
The current Northeast Monsoon conditions typically persist over the ASEAN region until late March, during which the prevailing low-level winds blow mainly from the northwest or northeast. From late March, the inter-monsoon period usually sets in over the ASEAN region, accompanied by a gradual increase in shower activity over the northern ASEAN region in April and May. Typically, the traditional dry season over the Mekong sub-region lasts until May.
For the March to May 2023 (MAM) period, an increased chance of above-normal rainfall is predicted for much of the northern half of the Maritime Continent as well as over central and eastern Mainland Southeast Asia. There is also an increased chance of below-normal rainfall for much of the southern half of the Maritime Continent. La Niña conditions are weakening and likely to be in ENSO neutral conditions in March to April 2023. La Niña event tends to bring wetter conditions to much of the ASEAN region. Above-normal temperature is predicted over much of the central and eastern Maritime Continent and Myanmar, with near-normal temperature predicted elsewhere.
The Mekong sub-region remains in its traditional dry season. The elevated hotspot activity and hazy conditions over much of the sub-region are likely to continue throughout the review period of MAM 2023, although an increased chance of above-normal rainfall and an increase in shower activities with a transition to inter-monsoon conditions from April 2023 may bring some respite. Under the persistent dry weather, widespread moderate to dense smoke haze and transboundary haze occurrences can be expected particularly over the northern, central, and western parts of the Mekong sub-region. For the southern ASEAN region, the overall hotspot activity is expected to be mostly subdued in MAM 2023 under the prevailing rainy weather. Nevertheless, isolated hotspots with occasional smoke plumes can still develop over the fire-prone areas in southern Sumatra and western Borneo during brief periods of drier conditions with the increased chance of below-normal rainfall expected in MAM 2023.
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 2023For March 2023, models predict above-normal rainfall over much of the northern half of the Maritime Continent as well as over central and southeastern Mainland Southeast Asia, while below-normal rainfall is predicted over much of the southwestern Maritime Continent and western half of Borneo.
For March 2023, above-normal rainfall is predicted over much of the northern half of the Maritime Continent, with highest likelihood over the Philippines, based on the multi-model ensemble (Figure 4). Below-normal rainfall is predicted over the western half of Borneo by all three models (Figures 1-3), with the NCEP and ECMWF models also predicting below-normal rainfall over parts of the southwestern Maritime Continent. The models’ skill is moderate to good for northern Maritime Continent for above-normal tercile category and low to moderate for central Borneo and the southwestern Maritime Continent for below-normal tercile category.
For Mainland Southeast Asia, based on the multi-model ensemble (Figure 4), there is an increase in chance of above-normal rainfall over the central and southeastern regions, with the ECMWF model predicting the largest extent of above-normal rainfall, followed by the NCEP model and then the UK Met Office with the smallest region of above-normal rainfall predicted. Elsewhere in Mainland Southeast Asia, models predict either below-normal rainfall or no dominant tercile. The models’ skill is generally low over much of Mainland Southeast Asia at this time of the year.
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| Figure 1a: Rainfall tercile summary predictions of NCEP model for March 2023. | Figure 1b: Rainfall tercile summary predictions of ECMWF model for March 2023 (contains modified Copernicus C3S information). |
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| Figure 1c: Rainfall tercile summary predictions of UK Met Office model for March 2023 (contains modified Copernicus C3S information). | Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for March 2023 (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 – May 2023 (MAM 2023)For MAM 2023, above-normal rainfall is predicted over much of the northern half of the Maritime Continent and over central and eastern Mainland Southeast Asia, while below-normal rainfall is predicted over much of the southern half of the Maritime Continent.
For MAM 2023, based on the multi-model ensemble (Figure 4), there is an increased chance of above-normal rainfall for much of the northern half of the Maritime Continent with highest chance over the Philippines, while an increased chance of below-normal rainfall is predicted over much of the southern half of the Maritime Continent. There is some difference between the models in the extent of the below-normal predictions over the southern Maritime Continent. The NCEP model has the largest extent over most of the region (Figure 1), followed by the ECMWF model with below-normal predicted except for the eastern-most region (Figure 2), and the UK Met Office model predicting below-normal rainfall only for the western half of the region (Figure 3). The models’ skill is moderate to relatively good over the northern and southwest 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 much of the central and eastern regions. The models’ skill for Mainland Southeast Asia is moderate to relatively good for the mentioned regions. Elsewhere in Mainland Southeast Asia, there is either no dominant tercile or model skill is low.
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| Figure 2a: Rainfall tercile summary predictions of NCEP model for MAM 2023. | Figure 2b: Rainfall tercile summary predictions of ECMWF model for MAM 2023 (contains modified Copernicus C3S information). |
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| Figure 2c: Rainfall tercile summary predictions of UK Met Office model for MAM 2023 (contains modified Copernicus C3S information). | Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for MAM 2023 (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 2023For March 2023, above-normal temperature is predicted over much of the southeastern Maritime Continent and Myanmar. Below- to near-normal temperature is predicted for the rest of the ASEAN region.
For March 2023, an increased chance of above-normal temperature is predicted over much of the southeastern Maritime Continent and Myanmar as seen in the multi-model ensemble (Figure 4). For the Maritime Continent, the UK Met Office model (Figure 3) has the largest region where an increased chance above-normal temperature is predicted (including Borneo), while the NCEP and the ECMWF models (Figures 1 and 2) predict above-normal temperature only over parts of eastern Indonesia. The models’ skill for above-normal temperature category is relatively good for the Maritime Continent and low to moderate for Myanmar.
Elsewhere in the ASEAN region, the multi-model ensemble predicts below-normal temperature over southeastern Mainland Southeast Asia and near-normal temperature generally elsewhere. The ECMWF model predicts the largest extent of below-normal temperatures covering much of central, eastern, and southern Mainland Southeast Asia. Model skill is low to moderate for most of Southeast Asia for near-normal tercile category and moderate for the below-normal tercile category.
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| Figure 3a: Temperature tercile summary predictions of NCEP model for March 2023. | Figure 3b: Temperature tercile summary predictions of ECMWF model for March 2023 (contains modified Copernicus C3S information). |
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| Figure 3c: Temperature tercile summary predictions of UK Met Office model for March 2023 (contains modified Copernicus C3S information). | Figure 3d: Temperature tercile summary predictions of multi-model ensemble model for March 2023 (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 – May 2023 (MAM 2023)For MAM 2023, above-normal temperature is predicted over much of the central and eastern Maritime Continent and Myanmar. Near-normal temperature is predicted over elsewhere.
For MAM 2023, all three models – NCEP, ECMWF and UK Met Office (Figures 1-3) – predict an increased chance of above-normal temperature over much of central and eastern Maritime Continent and over Myanmar, with highest probability over the eastern Maritime Continent. The ECMWF and UK Met Office models predict larger extent of above-normal temperatures over the Maritime Continent, covering Sumatra, Borneo, and eastern Maritime Continent, while the NCEP model predicts near-normal temperatures for Sumatra and above-normal for the rest of the mentioned regions.
Elsewhere, the models generally predict near-normal temperatures based on the multi-model ensemble (Figure 4). The models’ skill is moderate to high for above-normal temperature, and low to moderate for near-normal temperature.
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| Figure 4a: Temperature tercile summary predictions of NCEP model for MAM 2023. | Figure 4b: Temperature tercile summary predictions of ECMWF model for MAM 2023 (contains modified Copernicus C3S information). |
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| Figure 4c: Temperature tercile summary predictions of UK Met Office model for MAM 2023 (contains modified Copernicus C3S information). | Figure 4d: Temperature tercile summary predictions of multi-model ensemble model for MAM 2023 (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.