Seasonal Forecast for June – August 2023
Updated 1 June 2023
Southwest Monsoon conditions are expected to be established from June 2023 and persist throughout the June to August (JJA) 2023 period. In the northern ASEAN region, the Southwest Monsoon is associated with the traditional rainy season that often brings widespread and persistent shower activities. Over the southern ASEAN region, the Southwest Monsoon season is characterised by drier conditions compared to other times of the year, as the monsoon rain band typically lies further north from the Equator. Overall, the prevailing low-level winds in the ASEAN region blow mainly from the southeast or southwest during this period.
For the June to August (JJA) 2023 period, an increased chance of below-normal rainfall is predicted for much of the southern ASEAN region, with highest likelihood over the southern Maritime Continent. ENSO neutral conditions are present but are likely to transition into El-Niño in the next few months. A positive Indian Ocean Dipole (IOD) is predicted to develop during June – August 2023. Warmer-than-normal temperature is predicted for much of the ASEAN region.
Hotspot activity in the northern ASEAN region is expected to be generally subdued by the prevailing wet weather throughout JJA 2023. In contrast, extended periods of dry weather are likely to prevail over the southern ASEAN region. Increased hotspot activity and smoke haze development can be expected over the fire-prone areas, with a risk of transboundary haze affecting parts of the region. In addition, there is an elevated chance for the hotspot and haze situation in the southern ASEAN region to be the most intense since 2019, contributed by an impending El Niño and positive IOD, with below-normal rainfall predicted for many parts of the region.
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 – June 2023For June 2023, models predict below-normal rainfall over much of the southern ASEAN region.
For June 2023, below-normal rainfall is predicted over much of the southern ASEAN region, with highest likelihood over southern Maritime Continent based on the multi-model ensemble (Figure 4). The ECMWF model shows the highest confidence for below-normal rainfall over the southern Maritime Continent (Figure 2), followed by the UK Met Office (Figure 3). The NCEP model predicts below-normal rainfall for the equatorial region with no dominant tercile for much of the southern Maritime Continent (Figure 1). The skill is moderate to good for the southern ASEAN region for the ECMWF model and low to moderate for the NCEP and UK Met Office models.
For the northern ASEAN region, above-normal rainfall over coastal parts of western Mainland Southeast Asia is predicted based on the multi-model ensemble (Figure 4). There is either disagreement between the models or no dominant tercile predicted over the rest of Mainland Southeast Asia and much of the Philippines (Figure 1-3). The models’ skill for all three terciles is low for most of the northern ASEAN region, although it is low to moderate for coastal parts of western Mainland Southeast Asia and the Philippines.
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| Figure 1: Rainfall tercile summary predictions of NCEP model for June 2023 (contains modified Copernicus C3S information). | Figure 2: Rainfall tercile summary predictions of ECMWF model for June 2023 (contains modified Copernicus C3S information). |
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| Figure 3: Rainfall tercile summary predictions of UK Met Office model for June 2023 (contains modified Copernicus C3S information). | Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for June 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 – June – August 2023 (JJA 2023)For JJA 2023, models predict an increased chance of below-normal rainfall for much of the southern ASEAN region and above-normal rainfall over western Mainland Southeast Asia and parts of the Philippines.
For JJA 2023, below-normal rainfall is predicted for much of the southern ASEAN region based on the multi-model ensemble (Figure 4). The ECMWF and UK Met Office models show high confidence for blow-normal rainfall over the western and central Maritime Continent (Figures 2 and 3, respectively), while the NCEP model is less certain of below-normal rainfall over these regions (Figure 1). The models show moderate to good skill for below-normal rainfall over most of the southern ASEAN region.
All models predict above-normal rainfall over western Mainland Southeast Asia and parts of the Philippines (Figures 1 – 3), with low to moderate model skill for below-normal rainfall for this region. Elsewhere in the northern ASEAN region, there is disagreement between the models, although there is a slight increase in chance of above-normal rainfall over southeastern Mainland Southeast Asia based on the multi-model ensemble (Figure 4).
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| Figure 1: Rainfall tercile summary predictions of NCEP model for JJA 2023 (contains modified Copernicus C3S information). | Figure 2: Rainfall tercile summary predictions of ECMWF model for JJA 2023 (contains modified Copernicus C3S information). |
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| Figure 3: Rainfall tercile summary predictions of UK Met Office model for JJA 2023 (contains modified Copernicus C3S information). | Figure 4: Rainfall tercile summary predictions of multi-model ensemble model for JJA 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 – June 2023For June 2023, above-normal temperature is favoured over much of the ASEAN region, with higher probabilities for above-normal temperature predicted over much of the Maritime Continent.
For June 2023, above-normal temperature is predicted over much of the Maritime Continent based on the multi-model ensemble (Figure 4). The models agree with high confidence on above-normal temperature over the eastern half of the Maritime Continent as well as the western Maritime Continent (Figures 1 -3). However, for the southern Maritime continent the NCEP model predicts above-normal temperature (Figure 1), while the ECMWF model predicts near-normal temperature (Figure 2) and the UK Met Office predicts near-to-below normal temperature (Figure 3). Models’ skill for above-normal temperature is relatively good for above-normal temperature over most of the Maritime Continent.
Models predict above-normal temperature over much of the Mainland Southeast Asia (Figure 4). The probability of above-normal temperature varies across models, with the ECMWF model predicting the highest probability over southern Mainland Southeast Asia (Figure 3), while the NCEP and UK Met Office models predict higher probabilities over parts of northern Mainland Southeast Asia (Figures 1 and 3, respectively). The models’ skill is relatively good for above-normal temperature for most of Mainland Southeast Asia.
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| Figure 1: Temperature tercile summary predictions of NCEP model for June 2023 (contains modified Copernicus C3S information). | Figure 2: Temperature tercile summary predictions of ECMWF model for June 2023 (contains modified Copernicus C3S information). |
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| Figure 3: Temperature tercile summary predictions of UK Met Office model for June 2023 (contains modified Copernicus C3S information). | Figure 4: Temperature tercile summary predictions of multi-model ensemble model for June 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 – June – August 2023 (JJA 2023)For JJA 2023, the models predict an increased chance of above-normal temperature over most of the ASEAN region.
For JJA 2023, above-normal temperature is predicted for most of the ASEAN region based on the multi-model ensemble (Figure 4). However, the probability of above-normal temperature is generally lower over the southern Maritime Continent compared to the rest of the ASEAN region. The models disagree on the dominant tercile over southern Maritime Continent, with NCEP predicting above normal temperature (Figure 1), the ECMWF predicting near-normal temperature (Figure 2) and the UK Met Office predicting below- to-near normal temperature (Figure 3). Both the ECMWF and UK Met Office models predict below-normal temperature over the western coast of Sumatra as well.
The model skill for predicting above-normal temperature for the ASEAN region is moderate to good. The model skill for near-normal temperature is low to moderate over southern Maritime Continent.
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| Figure 1: Temperature tercile summary predictions of NCEP model for JJA 2023 (contains modified Copernicus C3S information). | Figure 2: Temperature tercile summary predictions of ECMWF model for JJA 2023 (contains modified Copernicus C3S information). |
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| Figure 3: Temperature tercile summary predictions of UK Met Office model for JJA 2023 (contains modified Copernicus C3S information). | Figure 4: Temperature tercile summary predictions of multi-model ensemble model for JJA 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.