Monthly Archives: September 2020

September 21, 2020

Subseasonal Weather Outlook (21 September – 4 October 2020)

Issued 21 September 2020
First forecast week: 21 September – 27 September
Second forecast week: 28 September – 4 October

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over the equatorial region in the first week (21 – 27 September), easing in most places except Papua in the second week (28 September – 4 October).

Warmer conditions are expected during the fortnight over most of Mainland Southeast Asia (except northern Myanmar), the Philippines and southern parts of Southeast Asia, with closer to normal temperatures in the equatorial region (corresponding to the wetter conditions in the rainfall outlook).

The previous Madden-Julian Oscillation (MJO) signal weakened after entering the Maritime Continent (Phase 4), just before the start of the forecast period. Most models predict this weak MJO signal to continue propagating across the Maritime Continent and over the Western Pacific.

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.

September 17, 2020

Review of Regional Haze Situation for August 2020

1.1 In August 2020, Southwest Monsoon conditions prevailed over the ASEAN region and the prevailing winds blew from the southeast or southwest. The location of the monsoon rain band north of the Equator, combined with the impact of Tropical Storms Sinlaku/Mekkhala and Typhoon Maysak, contributed to the rainy weather over most of the northern ASEAN region (Figure 1). In the southern ASEAN region, the weather was mostly dry in the first half of the month followed by an increase in shower activities over the equatorial region in the latter half of the month.

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

1.2 The hotspot counts were observed to be relatively low when compared to the same review period in previous years for most parts of the ASEAN region due to the wetter weather (Figure 2 and Figure 3).

Figure 2: Hotspot counts for the southern ASEAN region for August 2016 – 2020. [Note: The hotspot count from 2019 is based on the NOAA-20 satellite, and based on the Suomi-NPP satellite for the period from 2016-2018.]

Figure 3: Hotspot count for the northern ASEAN region for August 2016 – 2020. [Note: The hotspot count from 2019 is based on the NOAA-20 satellite, and based on the Suomi-NPP satellite for the period from 2016-2018.]

1.3 In August 2020, isolated hotspots were detected mostly in Kalimantan and Sumatra, as well as in some parts of Java, Nusa Tenggara and Viet Nam (Figure 4). While most of the hotspots detected in the ASEAN region were short-lived, a cluster of hotspots with high fire intensity (Figure 5) was observed to persist for more than a week (Figure 4) in West Kalimantan. Isolated smoke plumes were observed to emanate from some of these hotspots and affected the western parts of Sarawak on 8 August 2020.

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

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

September 11, 2020

Review of Regional Weather for August 2020

Print Version

1. Overview

1.1 During August 2020, most of Mainland Southeast Asia experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded in Lao PDR and Rakhine State, Myanmar, based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). In contrast, northern Philippines recorded below-average rainfall. For the southern half of Southeast Asia, below- to near-average rainfall was recorded in the west, and near- to above-average rainfall in the east. There is some discrepancy between the two satellite datasets for the below-average rainfall for Sumatra and Peninsular Malaysia, with more extensive drier conditions based on CMORPH-Blended (Figure 1, right) compared to GSMaP-NRT (Figure 1, left).

1.2 The observed large-scale rainfall anomaly pattern for southern Southeast Asia (i.e. below-average rainfall in the west and above-average rainfall in the east) is broadly consistent with the predictions from the subseasonal weather outlooks for August 2020 (27 July – 9 Aug, 10 – 23 Aug). 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 August 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 of Southeast Asia experienced above-average temperature during August 2020, apart from central and northern Mainland Southeast Asia where the temperature was closer to the climatological average (Figure 2). Warmer anomalies (≥ 0.5°C) occured mainly in coastal regions, with the warmest anomalies in August (≥ 1.0°C) in southeastern Southeast Asia.

Figure 2: Temperature anomalies for the month of August 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 At the start of August, a Madden-Julian Oscillation (MJO) signal was present in the maritime continent (Figure 3). The signal then weakened and quickly moved across the Pacific reaching the Western Hemisphere (Phase 8) by the middle of the month. In the second half of August, the once again substantial MJO signal continued to propagate eastward with the enhanced phase reaching the eastern Indian Ocean (Phase 3) by the end of the month. At this time of year, phases 4 and 5 typically bring above-average rainfall for regions in Southeast Asia between 5° and 20°N, while phases 8 and 1 typically bring below-average rainfall for the same region. Phases 2 and 3 tend to bring wetter conditions to the western maritime continent (which was not evident in the rainfall anomalies for August 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).

September 9, 2020

ASMC Bulletin (Issue #6, Sep 2020)

September 7, 2020

Subseasonal Weather Outlook (7 – 20 September 2020)

Issued 7 September 2020
First forecast week: 7 September – 13 September
Second forecast week: 14 September – 20 September

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For the northern part of Southeast Asia, drier conditions are predicted to persist for the first week (7 – 13 September), before returning to normal in the second week (14 – 20 September). For the equatorial region, wetter conditions are predicted in the first week, gradually easing in most places the following week, except for southern Thailand, northern Borneo and northern Sulawesi.

Warmer conditions are expected during the fortnight over northern and southern parts of Southeast Asia, with closer to normal temperatures in the equatorial region (corresponding to the wetter conditions in the rainfall outlook).

At the start of September, a Madden-Julian Oscillation (MJO) signal was present in the Indian Ocean (Phase 3). Most models predict this MJO to decay by the start of the first week of the forecast.

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.