Monthly Archives: June 2020

June 29, 2020

Subseasonal Weather Outlook (1 – 15 July 2020)

Issued 29 June 2020
Valid for weeks 1 and 2: 1 – 15 July 2020

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

In the first fortnight of July 2020, wetter conditions are expected over the equatorial regions of Southeast Asia, whereas drier conditions are expected over the northern and central parts of the Philippines.

In the first week of July, wetter conditions are expected over the southern parts of Mainland Southeast Asia.

Warmer conditions are expected over the northern and central parts of the Philippines, and the southern parts of the Maritime Continent for the first fortnight of July. For Mainland Southeast Asia, there is a higher likelihood of warmer conditions in the first week of July.

No discernible Madden-Julian Oscillation (MJO) signal is observed and there is no consistent signal in the models’ predictions for an MJO to develop in 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.

June 15, 2020

Subseasonal Weather Outlook (16 – 30 June 2020)

Issued 15 June 2020
Valid for weeks 3 and 4: 16 – 30 June 2020

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are expected over most parts of the equatorial Maritime Continent in the second fortnight of June 2020.

Over northern Southeast Asia, drier conditions are expected in the second fortnight of June except for some coastal parts of Myanmar where wetter conditions are expected in Week 3.

Warmer conditions are expected over most parts of northern Southeast Asia, especially in Week 4. A higher likelihood of warmer conditions is also expected around the southeastern part of the Maritime Continent.

A Madden-Julian Oscillation (MJO) is currently present over the Indian Ocean. During the forecast period, most models predict the MJO to slow down as it enters the Maritime Continent. If the MJO continues to propagate, this would increase the likelihood of wetter conditions in the Maritime Continent.

Review of Regional Weather for May 2020

Print Version

1. Overview

1.1 The rainfall anomalies for May 2020 can be partitioned broadly into northern and southern Southeast Asia (Figure 1). Over northern Southeast Asia (10-20°N), most of the coastal regions and some areas further inland experienced below-average rainfall. As this period marks the start of the Southwest Monsoon season, this could mean a slight delay in the onset of the monsoon season for some parts of northern Southeast Asia. There are differences in the intensity and spatial extent between the two data sources, GSMaP-NRT and CMORPH-Blended. For CMORPH-Blended, the areas with below-average rainfall extended further inland over Mainland Southeast Asia, apart from coastal Myanmar (wetter based on CMORPH-Blended, but drier based on GSMaP-NRT).

1.2 For southern Southeast Asia, most of the Maritime Continent region experienced above-average rainfall amounts. The more intense rainfall was observed over the western Maritime Continent (parts of Java, Sumatra, and Borneo). Over the eastern side (Maluku Islands and West Papua), mostly drier conditions were observed. This large-scale rainfall anomaly pattern (below-rainfall conditions in the north and above-average conditions in the south) is broadly consistent with the predictions in the subseasonal weather outlooks for the first and second fortnights of May 2020, except for the eastern Maritime Continent region.

Figure 1: Rainfall anomalies for the month of May 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 Southeast Asia experienced above-average temperature during May 2020 (Figure 2). Much warmer anomalies (≥ 1.0°C) are concentrated over Mainland Southeast Asia and West Papua; thus broadly aligned to areas that experienced drier conditions during the same period.

Figure 2: Temperature anomalies for the month of May 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) retreated from Phase 4 into the unit circle (weak signal) during the first and second weeks of May 2020. The MJO then emerged over the Indian Ocean (Phase 2) in the later part of the second week, weakened momentarily during Phase 3 and Phase 4, and re-emerged to propagate strongly eastwards in Phase 6, Phase 7, and Phase 8 in the last week of May 2020. Typically, the Maritime Continent experiences drier conditions during Phase 6 to Phase 8 of the MJO. For May 2020, this is only true for the eastern Maritime Continent (see 1.2). The western Maritime Continent rainfall anomaly, on the other hand, could have been dominated by the wetter conditions that prevailed in the first three weeks.

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).

June 4, 2020

Review of Regional Haze Situation for May 2020

1.1 The inter-monsoon conditions that prevailed over the ASEAN region in May 2020 transitioned to Southwest Monsoon conditions in late-May 2020. The presence of the monsoon rain band further north of the Equator brought an increase in shower activities over the Mekong sub-region in the latter half of the month. In the southern ASEAN region, scattered showers fell over most parts of the region. During the review period, the prevailing winds over the ASEAN region were light and variable in direction but gradually shifted to blow from the southeast or southwest with the start of the Southwest Monsoon season.

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

1.2 In early May 2020, most of the hotspot activities were detected in Lao PDR, Myanmar and Viet Nam. An increase in shower activities over the northern ASEAN region during the month contributed to a gradual reduction of hotspot activities in the Mekong sub-region. In the southern ASEAN region, the hotspot activities continued to remain subdued due to wet weather over many parts of the region.

Figure 2: Hotspot count for the northern ASEAN region for May 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 May 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 May 2020, clusters of hotspots were detected mostly in the northern part of Lao PDR. These hotspots persisted for about one week. Isolated hotspots were also detected in Cambodia and Viet Nam on many days. In the southern ASEAN region, short-lived isolated hotspots were detected on some days.

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

1.4 In May 2020, hotspot activities were more intense in the northern parts of Myanmar and Lao PDR. Some of these hotspot activities contributed to the occurrence of smoke haze in the sub-region.

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

1.5 The increase in shower activities brought a further improvement to the haze situation in the Mekong sub-region in the first half of May 2020. During periods of drier weather in early May 2020, moderate smoke haze was observed mainly in the northern parts of Lao PDR. Localised smoke plumes were also observed to emanate from some of the hotspots in the Mekong sub-region on some days. In the southern ASEAN region, while there were localised hotspot activities, no significant smoke haze was observed.

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 May 2020.