Monthly Archives: July 2020

July 27, 2020

Subseasonal Weather Outlook (27 July – 9 August 2020)

Issued 27 July 2020
First forecast week: 27 Jul – 2 Aug
Second forecast week: 3 Aug – 9 Aug

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

In the first forecast week (27 Jul – 2 Aug), wetter conditions are expected over much of the equatorial region, as well as southern and eastern coastal regions of Mainland Southeast Asia and the Philippines.

In the second forecast week (3 Aug – 9 Aug), wetter conditions are expected over eastern Southeast Asia and over the southern and eastern regions of Mainland Southeast Asia as highlighted in the rainfall map.

Drier conditions are expected over southern parts of Southeast Asia (southern Sumatra and Java). In the second week, drier conditions are also expected to develop over the rest of Sumatra and the region covering Peninsular Malaysia and western Borneo.

Warmer conditions are expected over northern Southeast Asia, particularly in the first forecast week. In the second week, warmer conditions are expected to develop over the western equatorial region, in line with the drier conditions.

While there are some signs of a Madden-Julian Oscillation (MJO) signal in the western Indian Ocean, the models are inconsistent in their predictions for the signal to continue during the forecast period.

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.

July 17, 2020

Review of Regional Haze Situation for June 2020

1.1 Southwest Monsoon conditions prevailed over the ASEAN region in June 2020. The prevailing winds in the region generally blew from the southeast or southwest. While the traditional dry season of the southern ASEAN region typically starts in June, during the review period, there have been persistent and widepread showers over the southern ASEAN region brought about by the close proximity of the monsoon rain band. The prevailing wet conditions over the Mekong sub-region during this period is typical of the traditional rainy season associated with the Southwest Monsoon of the northern ASEAN region.

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

1.2 2. In Jun 2020, the number of hotspots detected in both the northern and southern ASEAN region remained generally subdued due to rainy weather. In particular, the total number of hotspots detected in the southern ASEAN region for Jun 2020 was the lowest ever recorded since year 2013.

Figure 2: Hotspot count for the northern ASEAN region for Jun 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.]

Figure 3: Hotspot count for the southern ASEAN region for Jun 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 While hotspot activities in the region remained subdued, isoted hotspots were still detected in parts of Viet Nam and Sumatra on some days. Localised smoke plumes were observed to emanate from some hotspots in Riau, Sumatra and Central Kalimantan. These hotspots however were short-lived and did not contribute to any significant smoke haze.

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

1.4 In June 2020, the fire intensity of hotspots detected across the region was low. There was no significant smoke haze observed based on satellite imageries and ground reports.

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

July 14, 2020

Review of Regional Weather for June 2020

Print Version

1. Overview

1.1 During June 2020, the region between 5°S and 15°N predominately experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded over northern Sulawesi, southern Thailand, southern Viet Nam, and western Borneo based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). For the Mainland Southeast Asia, above-average rainfall inland conditions were observed over northern Myanmar and northern Laos, whereas below-average rainfall conditions were observed along coastal regions of western Myanmar and northern Viet Nam. Below-average rainfall was also recorded over northern parts of the Philippines and some parts of the eastern Maritime Continent (Java and Nusa Tenggara, Indonesia).

1.2 The observed large-scale rainfall anomaly patterns (i.e. above-average rainfall conditions in the equatorial regions and below-average conditions in northern parts of the Philippines and coastal parts of northern Viet Nam) are broadly consistent with the predictions in the subseasonal weather outlooks for the first and second fortnights of June 2020, except for some parts of the eastern Maritime Continent region where drier conditions were observed.

Figure 1: Rainfall anomalies for the month of June 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 June 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.

Figure 2: Temperature anomalies for the month of June 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 The Madden-Julian Oscillation (MJO) signal propagated eastwards from Phase 1 (Western Hemisphere) to Phase 2 (Indian Ocean) during the first two weeks of June. Typically for the region in June, Phases 1 and 2 bring drier conditions in northern Southeast Asia while Phase 2 brings wetter conditions in the western Maritime Continent. Subsequently the MJO then stalled, before weakening and becoming indiscernible by early part of the third week of June, obscured by other equatorial atmospheric waves. Towards the last few days of June, a new MJO signal re-emerged in Phase 1 (Western Hemisphere).

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).

July 13, 2020

Subseasonal Weather Outlook (16 – 31 July 2020)

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

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

In the second fortnight of July 2020, wetter conditions are expected over much of the equatorial region of Southeast Asia. While the likelihood of these wetter conditions is similar for both weeks in the central and eastern equatorial region (Borneo, eastern Indonesia), there is some difference in the likelihood in the western equatorial region. In Week 3, wetter conditions are more likely for Sumatra and the southern Malay Peninsula, while in Week 4, wetter conditions are more likely for southern Thailand and southern Myanmar.

For northern Southeast Asia, drier conditions are expected over much of this region in Week 3, and becoming confined to western Myanmar in Week 4. During Week 3, the largest dry anomalies are expected over Myanmar, Lao PDR, and the northern Philippines.

Warmer conditions are expected over northern Southeast Asia, particularly in Week 3.