Seasonal Forecast for April – June 2024
Updated 2 Apr 2024
The Northeast Monsoon conditions have eased and there has been a transition to the inter-monsoon period from the end of March 2024. Typically, the inter-monsoon conditions prevail over the ASEAN region throughout April and May before the gradual onset of the Southwest Monsoon from end May to early June. The Mekong sub-region continues to experience its traditional dry season which could extend into May before easing. For the southern ASEAN region, occasional shower activities are expected during the outlook period of April to June 2024 (AMJ). From the end of May onwards, the prevailing winds gradually transition from light and variable to mainly southeast to southwest as the inter-monsoon period gives way to the Southwest Monsoon, along with the start of the dry season for parts of the southern ASEAN region.
For April to June (AMJ) 2024 period, models predict an increased chance of above-normal rainfall over the southern ASEAN region and below-normal rainfall over the northern ASEAN region. El Niño conditions are predicted to transition to neutral during April-May 2024. The Indian Ocean Dipole (IOD) is currently neutral. Above-normal temperature is predicted for the ASEAN region for AMJ 2024. The effect of El Niño conditions may still be present for a while after its decay. El Niño tends to bring drier and warmer conditions to much of the region at this time of year.
With below-normal rainfall expected over the northern ASEAN region during the outlook period of AMJ 2024, elevated hotspot activity and widespread transboundary haze over much of the Mekong sub-region are expected to persist at least till the first half of April 2024, before gradually improving during the inter-monsoon period as wetter conditions return to the sub-region. Over the southern ASEAN region, above-normal rainfall is likely and the overall hotspot activity is expected to remain subdued during the outlook period. However, an increased chance of hotspot and haze activities are expected in June as the traditional dry season for the region sets in.
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 April 2024, above-normal rainfall is predicted for much of the southern ASEAN region and below-normal over the northern ASEAN region.
For April 2024, above-normal rainfall is predicted with low likelihood for much of the southern ASEAN region based on the multi-model ensemble (Figure 4). The ECMWF model (Figure 2) shows the highest confidence and the largest extent of the above-normal rainfall over the equatorial region, followed by the UK Met Office model (Figure 3), and the NCEP model (Figure 1) predicting a mix of near- to above-normal rainfall. For above-normal rainfall over the southern ASEAN region, models’ skill is moderate to good for the ECMWF and UK Met Office models, and low to moderate for the NCEP model.
Below-normal rainfall is predicted over the northern ASEAN region, based on the multi-model ensemble (Figure 4). The ECMWF model (Figure 2) predicts below-normal rainfall over these regions with highest likelihood, followed by the UK Met Office model (Figure 3) and then the NCEP model (Figure 1). The models’ skill is generally good for the northern Maritime Continent and moderate to good for Mainland Southeast Asia.
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| Figure 1: Rainfall tercile summary predictions of NCEP model for April 2024 (contains modified Copernicus C3S information). | Figure 2: Rainfall tercile summary predictions of ECMWF model for April 2024 (contains modified Copernicus C3S information). |
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| Figure 3: Rainfall tercile summary predictions of UK Met Office model for April 2024 (contains modified Copernicus C3S information). | Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for April 2024 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological rainfall’s lower tercile boundary for April based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for April 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 AMJ 2024, above-normal rainfall is predicted for the southern ASEAN region with below-normal rainfall for the northern ASEAN region.
For AMJ 2024, above-normal rainfall is predicted for the southern ASEAN region based on the multi-model ensemble (Figure 4). While the ECMWF and UK Met Office models (Figure 2 and 3) show high confidence of above-normal rainfall over the southern ASEAN region, the NCEP model (Figure 1) has low likelihood of above-normal rainfall for the region. Models’ skill is moderate to good for above-normal rainfall over the southern ASEAN region.
Below-normal rainfall is predicted over the northern ASEAN region, based on the multi-model ensemble (Figure 4). All three models are in agreement with the below-normal rainfall over much of Mainland Southeast Asia. Over the Philippines, both the ECMWF and UK Met Office models (Figure 2 and 3) show high confidence for below-normal rainfall, followed by the NCEP model (Figure 1) showing moderate confidence over the region. The models’ skill for below-normal rainfall is relatively good over Philippines and moderate to good over Mainland Southeast Asia.
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| Figure 1: Rainfall tercile summary predictions of NCEP model for AMJ 2024 (contains modified Copernicus C3S information). | Figure 2: Rainfall tercile summary predictions of ECMWF model for AMJ 2024 (contains modified Copernicus C3S information). |
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| Figure 3: Rainfall tercile summary predictions of UK Met Office model for AMJ 2024 (contains modified Copernicus C3S information). | Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for AMJ 2024 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological rainfall’s lower tercile boundary for AMJ based on CHIRPS (reference period: 1991-2020). | Figure 6: Average climatological rainfall’s upper tercile boundary for AMJ 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 April 2024, above-normal temperature is predicted over the ASEAN region.
For April 2024, above-normal temperature is predicted over the ASEAN region based on the multi-model ensemble (Figure 4). All three models agree with high confidence on above-normal temperature over the Maritime Continent and most of Mainland Southeast Asia. Models’ skill for predicting above-normal temperature is good over the Maritime Continent as well as over much of Mainland Southeast Asia.
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| Figure 1: Temperature tercile summary predictions of NCEP model for April 2024 (contains modified Copernicus C3S information). | Figure 2: Temperature tercile summary predictions of ECMWF model for April 2024 (contains modified Copernicus C3S information). |
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| Figure 3: Temperature tercile summary predictions of UK Met Office model for April 2024 (contains modified Copernicus C3S information). | Figure 4: Temperature tercile summary predictions of multi-model ensemble model for April 2024 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological temperature for April 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 AMJ 2024, the models predict an increased chance of above-normal temperature over the ASEAN region.
For AMJ 2024, above-normal temperature is predicted over the ASEAN region based on the multi-model ensemble (Figure 4). All three models agree with high confidence on above-normal temperature over most of the region. Models’ skill for predicting above-normal temperature for the ASEAN region is good over most of the region.
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| Figure 1: Temperature tercile summary predictions of NCEP model for AMJ 2024 (contains modified Copernicus C3S information). | Figure 2: Temperature tercile summary predictions of ECMWF model for AMJ 2024 (contains modified Copernicus C3S information). |
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| Figure 3: Temperature tercile summary predictions of UK Met Office model for AMJ 2024 (contains modified Copernicus C3S information). | Figure 4: Temperature tercile summary predictions of multi-model ensemble model for AMJ 2024 (contains modified Copernicus C3S information). |
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| Figure 5: Average climatological temperature for AMJ 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.