Monthly Archives: April 2019

April 24, 2019

Alert20190424 – Downgrade of Alert Level 3 to Alert Level 2 for the Mekong sub-region

Downgrade of Alert Level 3 to Alert Level 2 for the Mekong sub-region

Since late March 2019, an increase in shower activities have helped to subdue hotspot activities in the southern Mekong sub-region. In recent days, the haze situation has further improved, and smoke haze from hotspots has been confined within Myanmar, and the northern parts of Thailand, Lao PDR and Viet Nam. The haze situation is expected to continue to improve with more rainy weather expected over the Mekong sub-region.

Based on surveillance by the NOAA-19 satellite, the total hotspot count in the Mekong sub-region have decreased from a high of 752 on 23 March 2019 to 70 and 59 on 22 and 23 April 2019 respectively.

Review of Land Fires and Smoke Haze Situation for First Fortnight of April 2019

1.1 An increase in shower activities over the southern Mekong sub-region since late-March helped to subdue hotspots and improve the haze situation over Cambodia, central and eastern Thailand, and the southern parts of Lao PDR and Viet Nam. However, smoke haze from persistent hotspots in the northern part of the Mekong sub-region continued to be observed. Dense smoke haze was observed on many days over eastern Myanmar, and the northern parts of Thailand and Lao PDR. Some smoke haze was blown to the northern parts of Viet Nam by the prevailing winds.

1.2 In the southern ASEAN region, hotspot activity was generally subdued except for isolated hotspots with smoke plumes detected in Riau, Sumatra, east coast of Peninsular Malaysia, and West Kalimantan in the second week of the fortnight.

Figure 1: Himawari-8 satellite image on 9 April 2019 shows smoke haze over the northern Mekong sub-region.

Figure 2: Himawari-8 satellite image on 7 April 2019 shows isolated smoke plumes in Peninsular Malaysia and Riau, Indonesia.

Figure 3: Himawari-8 satellite image on 7 April 2019 shows localised smoke plumes in West Kalimantan.

Review of Regional Weather Conditions for First Fortnight of April 2019

Print Version

1. Review of Regional Weather Conditions for First Fortnight of April 2019

1.1 The ASEAN region is under the influence of inter-monsoon conditions. Southwesterly or westerly winds prevailed over the Mekong sub-region, with Myanmar experiencing stronger-than-usual westerly winds along the coast. Winds were generally weak in the southern ASEAN region, except for the area around Papua and south of Kalimantan where there were stronger-than-usual westerly or northwesterly winds due to Typhoon Wallace and a developing low pressure system in the Timor Sea.

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Figure 1: 5000 ft average winds (left) and anomalies (right) for 1 – 15 April 2019. (Source: JMA)

1.2 Inter-monsoon conditions contributed to an increase in showers compared to March 2019 over the northern ASEAN region. However, dry weather continued to persist over many areas in Myanmar, northern Thailand and northern Lao PDR.

1.3 In the southern ASEAN region, showers fell over many parts of the region. Drier-than-average conditions were observed over northern Sumatra, east coast of Peninsular Malaysia, Sabah, Sarawak, and West Kalimantan.

Figure 2: Daily average rainfall for the ASEAN region in the First Fortnight of April 2019. (Source: JAXA Global Satellite Mapping of Precipitation)

Figure 3: Percent of average rainfall for 1 – 15 April 2019. The rainfall data may be less representative for areas with a less dense rainfall network. Hatched areas indicate climatology dry mask (average daily rainfall below 1 mm). (Source: IRI NOAA/NCEP CPC Unified Precipitation Analyses)

1.4 The Madden-Julian Oscillation (MJO) signal remained weak during the first fortnight of April 2019 and had no significant influence on the weather over the ASEAN region (Figure 4).

Figure 4: The MJO phase diagram (blue for April 2019). The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or indiscernible. (Source: Bureau of Meteorology)

1.5 The sea surface temperatures over the tropical Pacific Ocean Nino 3.4 region remained warm and close to El Niño thresholds. However, other indicators of El Niño Southern Oscillation such as the strength of trade winds and sea level pressure difference between the eastern and western tropical Pacific Ocean were close to normal.

April 13, 2019

Review of Regional Weather Conditions for Second Fortnight of March 2019

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1. Review of Regional Weather Conditions for Second Fortnight of March 2019

1.1 The Northeast Monsoon season gradually weakened and transitioned to inter-monsoon conditions in the second fortnight of March 2019. The prevailing winds over the Mekong sub-region were generally weak and variable in direction, while that in the southern ASEAN region, were blowing from the southwest and northwest. Over Java, there were westerly and southwesterly anomalies due to low pressure systems that developed south of Java during the fortnight. Figure 1 shows the average and anomalous winds at 5000 feet.

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Figure 1: 5000 ft average winds (left) and anomalies (right) for 16 – 31 March 2019. (Source: JMA)

1.2 The transition to inter-monsoon conditions during the latter part of the fortnight brought an increase in rainfall over southern parts of the Mekong sub-region. However, dry conditions prevailed over Myanmar, and the northern parts of Lao PDR and Thailand (Figure 2). In the southern ASEAN region, areas along the equatorial region, including southern Thailand, Peninsular Malaysia, Sarawak, northern and central Sumatra and West Kalimantan received below-average rainfall under the influence of a persistent dry air mass extending from the Pacific Ocean over the Southeast Asia region (Figure 3).

Figure 2: Daily average rainfall for the ASEAN region in the second fortnight of March 2019. (Source: JAXA Global Satellite Mapping of Precipitation)

Figure 3: Percent of average rainfall for 16 – 31 March 2019. The rainfall data may be less representative for areas with a less dense rainfall network. Hatched areas indicate climatology dry mask (average daily rainfall below 1 mm). (Source: IRI NOAA/NCEP CPC Unified Precipitation Analyses)

1.3 The Madden-Julian Oscillation (MJO) signal remained weak during the second fortnight of March 2019 and had no significant influence on the weather over the ASEAN region (Figure 4).

Figure 4: The MJO phase diagram (green for March 2019). The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or indiscernible. (Source: Bureau of Meteorology)

1.4 The sea surface temperatures over the tropical Pacific Ocean Nino 3.4 region were warm and close to the El Niño thresholds. However, there was little atmospheric response observed, such as the lack of consistent weaker-than-average trade winds and large-scale rainfall patterns over the tropical Pacific.

Review of Land Fires and Smoke Haze Situation for Second Fortnight of March 2019

1.1 Dry weather prevailed over the Mekong sub-region in the second fortnight of March 2019. As a result, smoke haze from persistent hotspots continued to be observed over many areas in the sub-region. In particular, dense smoke haze persisted over parts of Lao PDR, Myanmar and Thailand on many days, and some smoke haze was blown by the prevailing winds toward northern Viet Nam (Figure 1). Toward the end of March 2019, an increase in shower activities over the southern parts of the Mekong sub-region helped improve the haze situation in Cambodia, southern Lao PDR and eastern Thailand (Figure 2).

1.2 In the southern ASEAN region, during periods of dry weather in the fortnight, isolated hotspots with localised smoke plumes were detected in Riau, Sumatra and Peninsular Malaysia (Figure 3). Elsewhere, scattered shower activities helped to keep hotspot activities subdued.

Figure 1: Himawari-8 satellite image on 21 March 2019 shows widespread smoke haze over the Mekong sub-region.

Figure 2: Himawari-8 satellite image on 31 March 2019 shows smoke haze largely confined over the northern Mekong sub-region, and increase in rainfall over the south toward end-March.

Figure 3: Himawari-8 satellite image on 18 March 2019 shows isolated hotspots with smoke plumes in Peninsular Malaysia and Riau, Sumatra.

April 12, 2019

Outlook for Land Fires and Smoke Haze Situation (16 – 30 Apr 2019)

Issued 12 April 2019

During the inter-monsoon period, more shower activities over the Mekong sub-region are expected. This can help to gradually subdue the persistent hotspot activities and bring an improvement to the haze situation there. In the southern ASEAN region, hotspot activities are expected to be generally subdued, although isolated hotspots with localised smoke plumes may occasionally emerge during brief periods of dry weather.

Subseasonal Weather Outlook (16 Apr – 30 Apr 2019)

Issued 12 Apr 2019
Valid for weeks 3 and 4: 16 Apr – 30 Apr

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

In the third week of April 2019, drier-than-usual conditions are expected to develop over parts of the Mekong sub-region, as well as over Malaysia and the Philippines. In the last week of the month, wetter-than-usual conditions are expected to develop over parts of Indonesia, with a possible development of Madden-Julian Oscillation (MJO) over the Indian Ocean. Most models predict the MJO to propagate slowly towards the east into the western Maritime Continent before weakening.

Warm conditions are expected to persist over the Mekong sub-region, as well as the northern part of Peninsular Malaysia.

The 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.