Monthly Archives: March 2020

March 30, 2020

Subseasonal Weather Outlook (1 – 15 April 2020)

Issued 30 March 2020
Valid for weeks 1 and 2: 1 – 15 April 2020

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For the first fortnight of April 2020, drier conditions are expected to persist over northern Sumatra, Peninsular Malaysia, southern parts of Mainland Southeast Asia, northern Borneo and most parts of the Philippines.

There is an increased chance of wetter conditions over some parts of the southeastern Maritime Continent in Week 1. For some parts of the southern Maritime Continent (Java), wetter conditions could redevelop in Week 2.

For temperature, warmer conditions are expected over most of Southeast Asia for the second fortnight of April 2020. Models predict a high chance of way-above average temperatures (exceeding 90%-tile) for some parts of Myanmar, especially in Week 1.

An Madden-Julian Oscillation (MJO) is currently present over the Indian Ocean and is expected to propagate eastward towards the Maritime Continent by Week 1. There is uncertainty across different models whether the MJO will continue to propagate to the western Pacific Ocean beyond Week 1.

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.

March 18, 2020

Review of Regional Weather for February 2020

Print Version

1. Overview

1.1 During February 2020, the region south of the equator predominately experienced above-average rainfall (Figure 1), with the largest positive anomalies (wetter conditions) over Java Island, Indonesia and southern Borneo. For north of the equator, above-average rainfall was observed over some coastal regions of Peninsular Malaysia while northern Borneo and most of the Philippines experienced below-average rainfall. The rainfall anomalies over mainland Southeast Asia were negligible, which is expected given that February is the drier time of the year for that region.

Figure 1: Rainfall anomalies for the month of February 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).

1.2 Overall, most of Southeast Asia experienced above-average temperature during February 2020 (Figure 2). The largest anomalies occurred over parts of Sulawesi, Papua and northern Viet Nam. As for the northern Southeast Asia, some parts of Cambodia, Thailand and Myanmar experienced below-average temperatures.

Figure 2: Temperature anomalies for the month of February 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 A Madden–Julian Oscillation (MJO) signal developed and strengthened over the Maritime Continent (Phases 4 and 5) during the first two weeks of February 2020 (Figure 3). The signal propagated eastwards with the main precipitation envelope reaching the western tip of Western Pacific (Phase 6). By the end of the second week, however, this MJO signal stalled, before weakening and becoming indiscernible in the third week of February. Broadly, Phases 4 and 5 normally bring wetter conditions for much of Southeast Asia in February, while Phase 6 brings a mixture of wetter and drier conditions.

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). 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).

2.2 The strong positive Indian Ocean Dipole (IOD) event from 2019, which had been weakening since November 2019, continued to weaken and returned to the neutral state in January 2020. The IOD typically remains in the neutral phase during the season from January to April.

March 13, 2020

Subseasonal Weather Outlook (16 – 31 March 2020)

Issued 13 March 2020
Valid for weeks 3 and 4: 16 – 31 March 2020

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For the second fortnight of March 2020, there is an increased chance of wetter conditions over some parts of the southern Maritime Continent in Week 3, easing in Week 4.

Drier conditions are expected to persist over northern Sumatra, Peninsular Malaysia, southern parts of Mainland Southeast Asia, northern Borneo and the Philippines throughout the fortnight.

For temperature, warmer conditions are expected over most parts of Mainland Southeast Asia for the second fortnight of March 2020. Warmer conditions are also expected over the southern-most parts of the Maritime Continent in Week 4.

A weak Madden-Julian Oscillation (MJO) is currently present in the eastern Maritime Continent. While most models predict the MJO to weaken at the start of the forecast period, there is a possibility of the MJO re-emerging over the Indian Ocean towards the end of Week 3.

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.

March 12, 2020

ASMC Bulletin (Issue #5, Mar 2020)

March 11, 2020

Alert20200311 – Activation of Alert Level 3 for the Mekong sub-region

Activation of Alert Level 3 for the Mekong sub-region

In recent days, there has been an escalation in hotspot activities and a deterioration in the haze situation in the Mekong sub-region, particularly in Lao PDR, Myanmar and Thailand. Based on surveillance by the NOAA-20 satellite, a total of 3002 and 2685 hotspots were detected in the Mekong sub-region on 9 Mar and 10 Mar respectively. Dense haze was observed in northern parts of Thailand and Lao PDR, and there have been occurrences of transboundary smoke haze over Myanmar and the northern parts of Thailand and Lao PDR during this period.

With the prevailing dry weather over the Mekong sub-region forecast to persist, a further deterioration in the hotspot and smoke haze situation can be expected.

March 9, 2020

Review of Regional Haze Situation for February 2020

1.1 In February 2020, Northeast Monsoon conditions prevailed over the ASEAN region. During this period, which is also traditional dry season in the northern ASEAN region, dry weather persisted over the Mekong sub-region. In the southern ASEAN region, there were scattered showers on most days. However, brief periods of dry weather were experienced in Malaysia, and northern and central Sumatra (Figure 1).

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

1.2 In the northern ASEAN region, dry weather gave rise to scattered hotspot activities in the Mekong sub-region. Based on surveillance by the NOAA-20 satellite, the highest number of hotspots was detected in Cambodia and Myanmar. In Lao PDR, Thailand and Viet Nam, the hotspot count in February 2020 was comparable to the same period in 2019 (Figure 2).

Figure 2: Hotspot count for the northern ASEAN region for Feb 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 the southern ASEAN region, hotspot activities were generally subdued in February 2020. The number of hotspots detected was slightly lower than the same period in 2019 (Figure 3).

Figure 3: Hotspot count for the southern ASEAN region for Feb 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.]

1.4 During February 2020, there were persistent hotspot activities in parts of the Mekong sub-region. In particular, significant clusters of hotspots were detected in Cambodia. In Thailand, clusters of hotspots were occasionally detected in its northern, northeastern and central regions. Hotspots were detected frequently in central and eastern Myanmar, and northern and southern Lao PDR during the month. In the southern ASEAN region, occasional isolated hotspots were detected mostly in Sumatra, Malaysia and Kalimantan.

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

1.5 Based on NOAA-20 satellite surveillance, hotspots with moderate to high fire intensity were detected mainly in Cambodia, southern Lao PDR and parts of Thailand and Myanmar.

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

1.6 In February 2020, hazy conditions were observed on many days in northern, northeastern and central Thailand, northern Cambodia and eastern Myanmar. Slight haziness was detected in northern Myanmar and southern Lao PDR on some days. There were also occasions of transboundary smoke haze when the prevailing winds transported the smoke haze from northern Thailand to northern Lao PDR, and from Cambodia to eastern Thailand.

Figure 6: Number of days with moderate to dense smoke haze observed over an area based on satellite imageries, ground observations and air quality reports in Feb 2020.