Monthly Archives: August 2020

August 21, 2020

Subseasonal Weather Outlook (24 August – 6 September 2020)

Issued 21 August 2020
First forecast week: 24 August – 30 August
Second forecast week: 31 August – 6 September

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

In the first week (24 – 30 August), wetter conditions are predicted around the equatorial region. The wetter conditions are expected to spread further southwards in the second week (31 August – 6 September). For the northern part of Southeast Asia, drier conditions are predicted for the fortnight, with higher likelihood in the first week.

Warmer conditions are expected during the fortnight over most parts of Southeast Asia except for the western Maritime Continent (parts of Peninsular Malaysia, Sumatra, and Borneo), corresponding to the rainfall outlook.

A Madden-Julian Oscillation (MJO) signal recently emerged in Western Hemisphere (Phase 8). Models predict the MJO to propagate eastwards towards Africa and the Indian Ocean during the fortnight.

The outlook is assessed for the region in general, where conditions are relative to the average conditions for the corresponding time of year. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.

August 14, 2020

Review of Regional Weather for July 2020

Print Version

1. Overview

1.1 During July 2020, most of the equatorial region experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded in the coastal equatorial regions based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). For the Mainland Southeast Asia, below-average rainfall was observed over northern Viet Nam, northern Philippines, and coastal Myanmar. This pattern of below-normal rainfall broadly follows the coastal regions between 15°N to 20°N, although there is some discrepancy between the two satellites for the Rakhine State, Myanmar, where the GSMaP-NRT (Figure 1, left) observed below-average rainfall, while CMORPH-Blended (Figure 1, right) observed near-average rainfall.

1.2 The observed large-scale rainfall anomaly pattern (i.e. above-average rainfall conditions in the equatorial regions and below-average rainfall for some regions of Mainland Southeast Asia and northern parts of the Philippines) is broadly consistent with the predictions in the subseasonal weather outlooks for July 2020 (1-15 July, 16-31 July).

Figure 1: Rainfall anomalies for the month of July 2020 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2019. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Most parts of equatorial Southeast Asia experienced near-average temperature during July 2020 (Figure 2), coinciding with areas that experienced wetter conditions during the same period. Warmer anomalies (≥ 0.5°C) are concentrated over Mainland Southeast Asia, northern parts of the Philippines and eastern Maritime Continent. This pattern is similar to the June temperature anomalies.

Figure 2: Temperature anomalies for the month of July 2020 based on ERA-5 reanalysis. The climatological reference period is 2001-2019. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 During the first half of July 2020, there was no coherent Madden-Julian Oscillation (MJO) signal. In Figure 3, the trace of the MJO moves between Phase 1 and Phase 2, with no clear eastward propagation. However, from the 19th of July, a clearer MJO signal formed and propagated eastward through the Indian Ocean (Phases 2 and 3), reaching the Maritime Continent at the end of the month. Typically in July, Phases 1 and 2 bring drier conditions in northern Southeast Asia while Phases 2 and 3 bring wetter conditions in the western Maritime Continent.

Figure 3: The MJO phase diagram. The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator (denoted in the text with the first day of the month in blue and the last day of the month in red). The distance of the index from the centre of the diagram is related to the strength of the MJO. Values within the grey circle are considered weak or indiscernible (data from the Bureau of Meteorology, Australia).

August 13, 2020

Review of Regional Haze Situation for July 2020

1.1 In July 2020, Southwest Monsoon conditions prevailed over the ASEAN region, with low-level winds blowing from the southeast or southwest. This period is typically associated with the traditional dry season over the southern ASEAN region and traditional rainy season over the northern ASEAN region. However, during most parts of the review period, the monsoon rain band remained over the equatorial Southeast Asia region and brought wet weather on many days to the equatorial southern ASEAN region. Around the last week of July 2020, the monsoon rain band shifted north, and this brought brief periods of dry weather over the southern ASEAN region, including Peninsular Malaysia, Sumatra and Kalimantan. This indicated the start of the traditional dry season for the southern ASEAN region. In the northern ASEAN region, rainy weather continued to prevail throughout the review period.

Figure 1: Average Daily Rainfall for Jul 2020. (Source: JAXA GsMaP)

1.2 The rainy weather in July 2020 contributed to the relatively low number of hotspots detected in the northern and southern ASEAN region, compared to the same period in previous years.

Figure 2: Hotspot count for the northern ASEAN region for Jul 2013 – 2020. [Note: Hotspot count from year 2019 onward is based on the NOAA-20 satellite, and for the period from year 2013-2018 is based on the Suomi-NPP satellite.]

Figure 3: Hotspot count for the southern ASEAN region for Jul 2013 – 2020. [Note: Hotspot count from year 2019 onward is based on the NOAA-20 satellite, and for the period from year 2013-2018 is based on the Suomi-NPP satellite.]

1.3 In July 2020, isolated hotspots were detected in parts of Viet Nam, Malaysia, Sumatra and Kalimantan. Occasionally, a few clusters of hotspots with localised smoke plumes were observed in Sumatra and Kalimantan, but the hotspots were short-lived and no significant smoke haze were observed.

Figure 4: Distribution of hotspots detected based on NOAA-20 satellite surveillance for Jul 2020.

1.4 The fire intensity of hotspots detected in the ASEAN region in July 2020 was low. No significant smoke haze was observed from satellite surveillance and ground reports.

Figure 5: Maximum fire intensity based on NOAA-20 satellite surveillance in Jul 2020.

August 8, 2020

Subseasonal Weather Outlook (10 – 23 August 2020)

Issued 8 August 2020

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

During the fortnight (10 Aug – 23 Aug), wetter conditions are expected over southern Southeast Asia particularly over the near-equatorial region as highlighted in the rainfall map.

Warmer conditions are expected during the fortnight over the southern and western parts of Southeast Asia.

A Madden-Julian Oscillation (MJO) signal developed over the Indian Ocean in the past fortnight, propagated eastwards and is now in the western Maritime Continent. Most models predict the MJO to continue propagating eastwards but may weaken in the first week.

The outlook is assessed for the region in general, where conditions are relative to the average conditions for the corresponding time of year. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.

August 3, 2020

Alert20200803 – Start of Dry Season for the Southern ASEAN Region

Start of Dry Season for the Southern ASEAN Region

In recent days, drier weather was observed over the southern ASEAN region, particularly in the southern parts of Sumatra and Kalimantan. Based on surveillance by the NOAA-20 satellite, a total of 19 and 5 hotspots were detected in Sumatra, while 2 and 3 hotspots were detected in Kalimantan, on 1 and 2 Aug 2020 respectively. There was no significant smoke haze observed in the vicinity of these hotspots.

The prevailing dry season is expected to continue into October 2020. For the next few months, above average rainfall is forecast in large parts of the region, which would help to reduce the risk of widespread land and forest fires. However, periods of dry weather can be expected occasionally, and this can lead to an increase in hotspot activities in the fire-prone areas.