Seasonal Forecast for July – September 2022
Updated 1 July 2022
Southwest monsoon conditions became fully established over the ASEAN region in June 2022, with the prevailing low-level winds blowing from the southeast or southwest. During the southwest monsoon, the monsoon rainband is typically located over the northern ASEAN region, leading the onset of the traditional wet season over the region. Over the southern ASEAN region, drier conditions become established as this region enters its traditional dry season.
For the July to September (JAS) 2022 period, an increased chance of above-normal rainfall is predicted for much of the southern ASEAN region, while there is small increase in chance of below-normal rainfall over parts of the band from 10°N to 20°N. Weak La Niña conditions are present, although these conditions are likely to continue weakening during July – August. After August, either La Niña or ENSO neutral conditions are expected. A negative Indian Ocean Dipole (IOD) is developing and expected to become established during July – August. Warmer-than-normal temperature is predicted for much of the ASEAN region, with the exception of near-normal temperature around Borneo.
In the southern ASEAN region, even though above-normal rainfall is forecast over much of the region, hotspot and smoke haze activities are expected to intensify as dry conditions become established in July – September 2022. This may lead to an increased likelihood of transboundary haze events if dry conditions are persistent over fire-prone regions. In the northern ASEAN region, hotspot and smoke haze activities are expected to remain subdued as the region enters its traditional wet season. However, a higher chance of below-normal rainfall is forecast in the coming months, which may lead to localised development of hotspots and smoke plumes over fire-prone areas.
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 – July 2022For July 2022, models predict above-normal rainfall over much of the southern ASEAN region.
For July 2022, above-normal rainfall is predicted over much of the southern ASEAN region, with highest likelihood over southern Maritime Continent (Figure 4). The exceptions include parts of the western Maritime Continent where no dominant tercile is predicted. The models’ skill is moderate to high for above-normal rainfall over the southern ASEAN region, with the highest skill over the southern Maritime Continent. Over the western Maritime Continent, the models’ skill is low.
For the northern ASEAN region, below-normal rainfall is predicted over much of the region between 10°N to 20°N based on the multi-model ensemble, with highest likelihood of drier conditions over southern Myanmar (Figure 4). Above-normal rainfall is predicted over parts of northern Mainland Southeast Asia, while no dominant tercile predicted over the rest of Mainland Southeast Asia. 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 southern Myanmar.
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| Figure 1a: Rainfall tercile summary predictions of NCEP model for July 2022. | Figure 1b: Rainfall tercile summary predictions of ECMWF model for July 2022 (contains modified Copernicus C3S information). |
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| Figure 1c: Rainfall tercile summary predictions of UK Met Office model for July 2022 (contains modified Copernicus C3S information). | Figure 1d: Rainfall tercile summary predictions of multi-model ensemble model for July 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.
Seasonal Rainfall Outlook – July – September 2022 (JAS) For JAS 2022, models predict above-normal rainfall for much of the southern ASEAN region.
For JAS 2022, above-normal rainfall is predicted for much of the southern ASEAN region based on the multi-model ensemble (Figure 4). The exception is over the western Maritime Continent where UK Met Office model (Figure 3) predicts near- to above-normal rainfall, the ECMWF model (Figure 2) predicts a mix of below- to above-normal rainfall, and the NCEP model (Figure 1) predicts below-normal rainfall over much of the region. The models show low to moderate skill over the western Maritime Continent and moderate to good skill over the rest of the Maritime Continent.
For the northern ASEAN region, below-normal rainfall is predicted over parts of the band from 10°N to 20°N based on the multi-model ensemble (Figure 4). While all three models predict below-normal rainfall over southwestern Mainland Southeast Asia, only ECMWF and UK Met Office models predict below-normal rainfall over southeastern Mainland Southeast Asia and parts of the Philippines. However, the models’ skill is low for below-normal rainfall for this region. Elsewhere in the northern ASEAN region, near- to above-rainfall is predicted, with low model skill over the region.
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| Figure 2a: Rainfall tercile summary predictions of NCEP model for JAS 2022. | Figure 2b: Rainfall tercile summary predictions of ECMWF model for JAS 2022 (contains modified Copernicus C3S information). |
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| Figure 2c: Rainfall tercile summary predictions of UK Met Office model for JAS 2022 (contains modified Copernicus C3S information). | Figure 2d: Rainfall tercile summary predictions of multi-model ensemble model for JAS 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 – July 2022For July 2022, the models predict above-normal temperature over most of the ASEAN region.
For July 2022, above-normal temperature is predicted over much of the ASEAN region based on the multi-model ensemble (Figure 4) with the exception over western Borneo where near-normal temperature is predicted. The NCEP and ECMWF models (Figures 1 and 2) predict near-normal temperature over western Borneo, while the UK Met Office model (Figure 3) predicts above-normal temperature. For the western Maritime Continent, the probability of above-normal temperature varies across models, with the UK Met Office model predicting the highest likelihood and followed by the NCEP and ECMWF models. For northern Mainland Southeast Asia, both the NCEP and UK Met Office models predict above-normal temperature, while ECMWF model predicts near-normal temperature.
The model skill is relatively good for above-normal temperature and moderate to good for near-normal temperature for most of the ASEAN region.
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| Figure 3a: Temperature tercile summary predictions of NCEP model for July 2022. | Figure 3b: Temperature tercile summary predictions of ECMWF model for July 2022 (contains modified Copernicus C3S information). |
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| Figure 3c: Temperature tercile summary predictions of UK Met Office model for July 2022 (contains modified Copernicus C3S information). | Figure 3d: Temperature tercile summary predictions of multi-model ensemble model for July 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.
Seasonal Temperature Outlook – July – September 2022 (JAS)For JAS 2022, the models predict above-normal temperature over most of the ASEAN region.
For JAS 2022, above-normal temperature is predicted for much of the ASEAN region based on the multi-model ensemble (Figure 4), with the exceptions over parts of Borneo and southern Sumatra where near-normal temperature is predicted. The NCEP model (Figure 1) predicts a high likelihood of above-normal temperature everywhere apart from southern Borneo. Both the ECMWF and UK Met Office models (Figures 2 and 3) predict relatively lower likelihood of above-normal temperature over northern Mainland Southeast Asia. Furthermore, the ECMWF model shows the largest extent of near-normal temperature around Borneo, followed by the UK Met Office model.
The model skill for above-normal temperature for most of the ASEAN region is moderate to good. The model skill for near-normal temperature is low to moderate over Borneo.
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| Figure 4a: Temperature tercile summary predictions of NCEP model for JAS 2022. | Figure 4b: Temperature tercile summary predictions of ECMWF model for JAS 2022 (contains modified Copernicus C3S information). |
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| Figure 4c: Temperature tercile summary predictions of UK Met Office model for JAS 2022 (contains modified Copernicus C3S information). | Figure 4d: Temperature tercile summary predictions of multi-model ensemble model for JAS 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.