Monthly Archives: October 2020

October 30, 2020

Alert20201030 – End of Dry Season for the Southern ASEAN Region

End of Dry Season for the Southern ASEAN Region

There have been more shower activities over the southern ASEAN region in the past few weeks. Based on surveillance by the NOAA-20 satellite, a total of 0 and 11 hotspots in Sumatra were detected on 28 and 29 Oct 2020 respectively, while 1 hotspot was detected in Kalimantan on each of these two days.

In the coming weeks, the prevailing winds are forecast to become light and blow from the northeast or northwest in the southern ASEAN region. Increased shower activities are also expected over most parts of the region. This will help to subdue hotspot activities and decrease the likelihood of transboundary haze. However, there could still be isolated hotspots with localised smoke haze during brief periods of drier weather.

Subseasonal Weather Outlook (2 – 15 November 2020)

Issued 30 October 2020
First forecast week: 2 November – 8 November
Second forecast week: 9 November – 15 November

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over the western Maritime Continent and southern Mainland Southeast Asia next week (2 – 8 November), easing in the second week (9 – 15 November). Parts of this region may however, experience near-normal rainfall, particularly along eastern coasts of Sumatra and the Malay Peninsula.

Wetter conditions are predicted over northern Myanmar in the first week (2 – 8 November). Wetter conditions are also predicted over northern Philippines during this first week, possibly extending to the west in the second week (9 – 15 November), although the location and extent of these wetter conditions will depend on tropical cyclone development.

No significant regional temperatures anomalies are expected in Southeast Asia in the next fortnight (2 – 15 November).

A Madden-Julian Oscillation (MJO) signal is present over the Pacific (Phase 6). Most models predict the MJO to continue propagating eastwards, potentially strengthening over the Western Hemisphere and Africa (Phases 8 and 1) in the second 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.

October 20, 2020

Review of Regional Haze Situation for September 2020

1.1 Southwest Monsoon conditions persisted over the ASEAN region in September 2020 and the prevailing winds blew mainly from the southeast or southwest. In the northern ASEAN region, rainy weather persisted throughout most of the month, particularly during the third week when Tropical Storm Noul made landfall over the Mekong sub-region and brought widespread showers. Average daily rainfall (Figure 1) was highest in coastal areas of Vietnam, Cambodia and Myanmar. In the southern ASEAN region, shower activities were frequently observed over many areas despite this period of the year being its traditional dry season. Average daily rainfall was highest in northwestern Borneo, northern Sumatra and West Papua while generally dry conditions were observed mainly over the Java Sea region.

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

1. 1.2 The hotspot counts in the ASEAN region for September 2020 remained relatively low when compared to the same review period in previous years due to wet weather (Figure 2 and Figure 3).

Figure 2: Hotspot counts for the southern ASEAN region for September 2016 – 2020. [Note: The hotspot counts from 2019 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 northern ASEAN region for September 2016 – 2020. [Note: The hotspot counts from 2019 are based on the NOAA-20 satellite, while those from 2016-2018 are based on the Suomi-NPP satellite.]

1.3 Isolated hotspots were detected in many parts of the ASEAN region in September 2020. In particular, persistent clusters of hotspots were detected in Viet Nam, the Lesser Sunda Islands, and some parts of Kalimantan (Figure 4). Localized smoke haze was also observed to emanate from some of the intense hotspots in Kalimantan during the second half of the month.

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

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

October 16, 2020

Subseasonal Weather Outlook (19 October – 1 November 2020)

Issued 16 October 2020
First forecast week: 19 October – 25 October
Second forecast week: 26 October – 1 November

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over eastern Mainland Southeast Asia and the Philippines for the next two weeks (19 October – 1 November), although the location and intensity of these wetter conditions will depend on tropical cyclone evolution. Wetter conditions are also predicted over parts of Java and southern Sumatra next week (19 – 25 October).

In general, drier conditions are predicted over the western Maritime Continent next week (19 – 25 October), gradually easing in the second week (26 October – 1 November). Parts of this region may however, experience near-normal conditions, particularly along eastern coasts of Sumatra and the Malay Peninsula.

Warmer temperatures are predicted over much of the equatorial region and northern Myanmar in the next fortnight (19 October – 1 November). Cooler temperatures than usual for this time of year are predicted over parts of Mainland Southeast Asia (Viet Nam, Lao PDR, northern Thailand and Cambodia).

A moderate Madden-Julian Oscillation (MJO) signal appears to be developing over the eastern Maritime Continent. Most models predict the MJO to propagate eastwards over the Pacific, although weakening slightly due in part to the La Niña conditions present.

October 15, 2020

Review of Regional Weather for September 2020

1. Overview

1.1 During September 2020, most of the equatorial region and southern parts of the Mainland Southeast Asia experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded in the coastal equatorial regions, southern Thailand, southern Cambodia and southern Viet Nam based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). In contrast, most of the Philippines recorded below-average rainfall. The rest of regions either experienced near-average rainfall for this time of year, or a mix between above- and below-average.

1.2 The observed large-scale rainfall anomaly pattern (i.e. above-average rainfall in the equatorial regions and below-average rainfall in the Philippines) is broadly consistent with the predictions from the subseasonal weather outlooks for September 2020 (7 – 20 Sep, 21 Sep – 4 Oct). The only notable anomalies forecasted for Mainland Southeast Asia were the wetter conditions over its southern and eastern coastal regions (linked to the MJO signal in phases 4 and 5).

Figure 1: Rainfall anomalies for the month of September 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 September 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 with the warmest anomalies in September (≥ 2.0°C) in northern Myanmar.

Figure 2: Temperature anomalies for the month of September 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 very slow-moving Madden-Julian Oscillation (MJO) signal was present in the Maritime Continent (Figure 3) during the month of September, momentarily strengthened in the middle of September for a few days and also towards the end of the month. At this time of year, phases 4 and 5 typically bring above-average rainfall for coastal regions in Southeast Asia between 5°N and 20°N.

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).

October 2, 2020

Subseasonal Weather Outlook (5 – 18 October 2020)

Issued 2 October 2020
First forecast week: 5 – 11 October
Second forecast week: 12 – 18 October

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over the eastern half of Southeast Asia for the next two weeks (5 – 18 October). During this time, models are also predicting wetter conditions for eastern Mainland Southeast Asia (Cambodia, Lao PDR, Viet Nam, and parts of Thailand), although the location of these wetter conditions will depend on tropical cyclone evolution. Wetter conditions are also expected over northern Sumatra in week 1 (5 – 11 October).

Warmer temperatures are predicted for the central and northern parts of Myanmar for the next two weeks. Warmer temperatures are also predicted to develop over the western Maritime Continent in week 2 (12 – 18 October).

A weak Madden-Julian Oscillation (MJO) signal was present over the Maritime Continent at the beginning of October (Phase 5). However, none of the models predict a coherent MJO signal to develop in the next two weeks.

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.