Monthly Archives: January 2021

January 26, 2021

Review of Regional Haze Situation for December 2020

1.1 Northeast Monsoon conditions prevailed over the ASEAN region in December 2020. In the northern ASEAN region, the prevailing winds blew mainly from the northeast or east during this month, with moderate to strong northeasterly winds over the southeastern Mekong sub-region on several days. Dry conditions developed over the Mekong sub-region, except over coastal areas of Viet Nam where isolated showers were observed on a few days. In the southern ASEAN region, isolated to scattered showers fell over most areas with the prevailing winds blowing mainly from the west or northeast. Rainfall activity was highest in southern Thailand, northern Peninsular Malaysia, Java and eastern coastal areas of the Philippines.

Figure 1: Average Daily Rainfall and Mean Wind for December 2020. (Source: JAXA GsMaP and GFS respectively)

1.2 The hotspot counts in the ASEAN region for December 2020 remained relatively low when compared to the same review period in previous years (Figure 2 and Figure 3).

Figure 2: Hotspot counts for the northern ASEAN region for the month of December between 2016 and 2020. [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2016-2018 are based on the Suomi-NPP satellite.]

Figure 3: Hotspot counts for the southern ASEAN region for the month of December between 2016 and 2020. [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2016-2018 are based on the Suomi-NPP satellite.]

1.3 Isolated to scattered hotspots were detected in many parts of the Mekong sub-region in December 2020. In particular, localised smoke plumes were observed to emanate from some of the isolated hotspots in Cambodia, Myanmar and Thailand. In the southern ASEAN region, the hotspot situation was subdued by rainy conditions.

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

Figure 5: Maximum fire intensity based on NOAA-20 satellite surveillance for December 2020.

January 22, 2021

Subseasonal Weather Outlook (25 January – 7 February 2021)

Issued 22 January 2021
First forecast week: 25 January – 31 January
Second forecast week: 1 February – 7 February

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For rainfall in Week 1 (25 – 31 January 2021), wetter conditions are predicted over much of the southern part of the ASEAN region. These wetter conditions are expected to become confined mainly to the region around Java in Week 2 (1 – 7 February 2021). There is also an increased chance of wetter conditions in Week 1 for southern parts of Mainland Southeast Asia as well as the northern Philippines.

For temperature, there is an increased chance of cooler conditions over the central part of the Maritime Continent, as well as southern Thailand, in Week 1 (25 – 31 January 2021). These cooler temperatures are expected to ease in Week 2 (1 – 7 February 2021).

The MJO signal that was present in the Maritime Continent (Phase 4) in the middle of January has weakened and is no longer discernable. Some models predict an MJO signal to emerge again in the Western Pacific (Phase 6 or 7) in Week 1.

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.

January 14, 2021

Alert20210114 – Activation of Alert Level 2 for the Mekong Sub-region

Activation of Alert Level 2 for the Mekong Sub-region

Dry weather in recent weeks over the Mekong sub-region has led to an escalation in the hotspot activities there. In particular, persistent hotspot clusters with smoke haze have been detected in Cambodia. Hotspots with smoke plumes have also been detected elsewhere in the Mekong sub-region. Based on surveillance by the NOAA-20 satellite, a total of 615 and 831 hotspots were detected in the Mekong sub-region on 12 and 13 Jan 2021 respectively.

The prevailing dry weather over the Mekong sub-region is expected to continue and the prevailing winds are forecast to blow from the north or northeast. Under these conditions, the hotspot and smoke haze situation there could deteriorate, and increase the risk of transboundary haze occurrence.

January 12, 2021

Review of Regional Weather for December 2020

1. Overview

1.1 During December 2020, coastal south-eastern parts of Mainland Southeast Asia and the Philippines experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded over northern and central Philippines, and southern Thailand based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended), partly linked to the tropical storm Krovanh in Week 3. For the rest of Mainland Southeast Asia, rainfall anomalies were negligible, expected at the start of dry season for the northern ASEAN region. A mix of above- and below-average rainfall was experienced for most regions in the equatorial region. There is some discrepancy between the two satellite datasets for the below-average rainfall for southern and central parts of Borneo, with more extensive drier conditions based on CMORPH-Blended (Figure 1, right) compared to GSMaP-NRT (Figure 1, left). Elsewhere in the southern Maritime Continent, wetter-than-average rainfall conditions were recorded over much of the land masses.

1.2 The observed large-scale rainfall anomaly pattern (i.e. above-average rainfall in regions linked to tropical storm and cyclone activity and below-average rainfall over parts of equatorial region) is broadly consistent with the predictions from the subseasonal weather outlooks for December 2020 (30 Nov – 13 Dec, 14 – 27 Dec).

Figure 1: Rainfall anomalies for the month of December 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 Colder-than-average temperatures were recorded over some regions of the eastern half of Mainland Southeast Asia in December 2020 (Figure 2). In contrast, warmer-than-average temperatures (more than 1°C warmer) were recorded over parts of Myanmar and northern Philippines. Warmer-than-average temperatures were also recorded over much of the equatorial region (3°S to 2°N). Elsewhere, the temperature for December was closer to average.

Figure 2: Temperature anomalies for the month of December 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 weak and slow-moving Madden-Julian Oscillation (MJO) signal was present in the Maritime Continent (Figure 3, Phase 5) at the start of December 2020, momentarily strengthened in Week 2 and then weakened as it reached Western Pacific (Phase 6) in the second half of December 2020. Phase 5 typically brings wetter conditions to eastern half of the Southeast Asia (observed in the rainfall anomalies for December 2020, Figure 1).

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).

2.2 Over the tropical Pacific Ocean, La Niña conditions were present. The sea surface temperatures in the central and eastern Pacific Ocean remained cool, with atmospheric indicators (cloudiness and wind anomalies) also remaining consistent with La Niña conditions. La Niña events tend to bring wetter-than-average conditions to much of Southeast Asia during the September to December period.

January 8, 2021

Subseasonal Weather Outlook (11 – 24 January 2021)

Issued 8 January 2021
First forecast week: 11 January – 17 January
Second forecast week: 18 January – 24 January

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For rainfall in Week 1 (11 – 17 January 2021), an increased chance of wetter conditions is predicted over much of the Maritime Continent. Drier conditions are also predicted for regions around the Gulf of Thailand in Week 1. In Week 2 (18 – 24 January 2021), the wetter conditions are expected to ease, apart from over the Philippines and northern Borneo, with drier conditions expected to develop in parts of the western Maritime Continent.

An increased chance of cooler conditions is predicted over much of Mainland Southeast Asia and parts of the western Maritime Continent in Week 1 (11 – 17 January 2021) due to a surge of cool air blowing southward from the northern Asian landmass. In Week 2 (18 – 24 January 2021), the cooler conditions are expected to ease for much of this area, apart from central parts of Mainland Southeast Asia. Warmer conditions are expected to develop in the central and eastern equatorial region in Week 2.

An MJO signal is present over the Indian Ocean (Phase 3). Some models predict it to propagate eastward, entering the Maritime Continent by the end of Week 1.