Monthly Archives: May 2020

May 30, 2020

14th ASEAN COF (21 May 2020, Online Correspondence)

Fourteenth Session of the ASEAN Climate Outlook Forum (ASEANCOF-14)

21st May 2020, Online Correspondence

Consensus Bulletin for June-July-August (JJA) 2020 Season

The ASEAN Climate Outlook Forum (ASEANCOF) is an avenue to collaboratively develop consensus-based seasonal climate outlooks and related information on a regional scale.

The forum outlook and its activities contribute significantly to one of the key roles of the ASEAN Specialised Meteorological Centre (ASMC), which is to conduct climate and seasonal prediction for the ASEAN region through pooling the expertise of ASEAN National Meteorological Services.

The fourteenth ASEANCOF (ASEANCOF-14) was organised by Meteorological Service Singapore as host of the ASEAN Specialised Meteorological Centre. Representatives from National Meteorological and Hydrological Services (NMHSs) of ASEAN Member States created a consensus forecast for the summer monsoon 2020 in the ASEAN region. The consensus for June-July-August (JJA) 2020 outlooks was achieved through online correspondence, including questionnaires and online discussions regarding the current conditions and predictions for the Southeast Asia region. In particular, the forum considered the possible influence of the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on the climate system over Southeast Asia.

Conditions and Outlook

Recent analysis of sea surface temperature (SST) anomalies over the equatorial Pacific indicate near average SSTs and ENSO neutral conditions are present. The international climate outlooks predict ENSO neutral conditions are likely to continue during JJA 2020, although there is potential that La Niña conditions may begin to develop towards the end of the period or later in the year. The previous positive Indian Ocean Dipole (IOD) weakened in January 2020 and the current IOD state is neutral. Some models predict a negative IOD event to develop during JJA, but with relatively high uncertainty at this time of year.

The consensus from ASEANCOF is an increased chance of a negative IOD event to develop during JJA while ENSO conditions are most likely to remain neutral during JJA. The Southwest (SW) Monsoon is expected to be weaker than normal, based on model predictions. However, local rainfall for some regions will depend on tropical cyclone activity, which is uncertain. For most countries, the onset of the SW monsoon is expected to be near-normal. However, the SW monsoon related rainfall may arrive later than normal for a few countries (Thailand and Viet Nam). Overall, the tropical cyclone frequency is expected to be near normal for JJA 2020.

Taking into consideration the national level forecasts, the present state of the climate, and the forecasts available from GPCs and other global centres, the forum agreed on the following consensus-based outlook for JJA 2020 for the Southeast Asia region:

RAINFALL

For the upcoming Northern Hemisphere summer season (June-July-August), normal- to above-normal rainfall is expected over much of the equatorial region (Brunei, Malaysia, Singapore, and northern parts of Indonesia) as well as northern Viet Nam and coastal central Viet Nam. Normal- to below-normal rainfall is expected over southern Myanmar, southern and northeastern Thailand, northern Philippines, parts of Lao PDR, and southeastern Indonesia. Elsewhere, normal or climatological probabilities are forecasted.

TEMPERATURE

Above-normal temperature is expected over most of Southeast Asia, although the probability of above-normal temperature is lower over Viet Nam and parts of Indonesia, and northern Philippines.

Refer to Annex A for reference on what is meant by “above, near, or below normal” in the outlook. For more information on the Northern Hemisphere Summer Monsoon outlook and further updates on the national scale, the relevant NMHSs should be consulted (see Annex B).

Consensus Maps for JJA 2020

The following maps provide the probabilistic outlooks for JJA 2020 season in terms of tercile categories of “Above Normal” (AN: upper tercile), “Near Normal (NN: middle tercile) and “Below Normal” (BN: lower tercile).

PROBABILISTIC RAINFALL OUTLOOK

PROBABILISTIC TEMPERATURE OUTLOOK

Meeting Documents

ASEANCOF-14 Outlook Bulletin

Acknowledgements

The Forum would like to convey its appreciation to the National Meteorological Services of the ASEAN Member States for sharing their national-level forecasts, the Global Producing Centres and other participating international climate modelling centres for their products and expertise made available for this Climate Outlook Forum.

May 28, 2020

Subseasonal Weather Outlook (1 – 15 June 2020)

Issued 28 May 2020
Valid for weeks 1 and 2: 1 – 15 June 2020

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are expected over most parts of the Maritime Continent in the first fortnight of June 2020. However, the wetter conditions may ease in the western Maritime Continent in Week 2.

Over Mainland Southeast Asia, particularly over parts of Myanmar and Lao PDR, drier conditions are expected in the first week of June. Drier conditions are also expected over northern and central parts of the Philippines over the first two weeks in June. The drier conditions are associated with weaker-than-normal Southwest Monsoon winds during the fortnight.

Warmer conditions are expected over most parts of Mainland Southeast Asia and northern and central Philippines, especially in Week 1. Over the Maritime Continent, a higher likelihood of warmer conditions is expected around the Java region.

A weak Madden-Julian Oscillation (MJO) is currently present over the Western Pacific. A number of models predict the MJO to continue propagating to the Western Hemisphere and Africa in the first week of June 2020, and possibly as far as the Indian Ocean in the week after.

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.

May 18, 2020

Alert20200518 – End of Dry Season for the Mekong Sub-region

End of Dry Season for the Mekong Sub-region

Over the past week, there have been increased showers over the Mekong sub-region. Based on surveillance by the NOAA-20 satellite, the total hotspot count in the Mekong sub-region remained low, with 147 and 69 hotspots detected on 16 May 2020 and 17 May 2020 respectively.

With rainy weather forecast over the Mekong sub-region in the coming days, hotspot activities are expected to be generally subdued.

May 15, 2020

Subseasonal Weather Outlook (16 – 31 May 2020)

Issued 15 May 2020
Valid for weeks 3 and 4: 16 – 31 May 2020

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For the second fortnight of May 2020, drier conditions are expected over western Mainland Southeast Asia (parts of Myanmar and Thailand), easing over Thailand and southern Myanmar in Week 4.

For most of the southern parts of Southeast Asia, there is an increased chance of wetter conditions, particularly in Week 3.

Warmer conditions are expected over most of Mainland Southeast Asia. Much of the Maritime Continent also has an increased chance of warmer conditions, except for parts of Peninsular Malaysia, Borneo and northern Philippines.

There was no clear Madden-Julian Oscillation (MJO) signal in the second week of May. While models predict an MJO to emerge over the Indian Ocean in Week 3, most models suggest the signal will be short-lived.

May 13, 2020

Review of Regional Weather for April 2020

Print Version

1. Overview

1.1 The rainfall anomalies for April 2020 were a mix of above-, near-, and below- average (Figure 1). Above-average rainfall was experienced by much of the western and southern parts of the Maritime Continent (Peninsular Malaysia, Sumatra, Java, and western parts of Borneo) as well as parts of Mainland Southeast Asia (northern Lao PDR, northern Viet Nam, southern Cambodia, and southern Thailand). The largest positive anomalies (wetter conditions) were recorded over Sumatra based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended), as well as over Java (CMORPH-Blended only). Below-average rainfall was recorded over central and southern Philippines, as well as northern Borneo. The rest of the regions either experienced near-average rainfall for this time of year, or a mix between above- and below-average. The observed large-scale rainfall anomaly pattern over the Southeast Asia region during April (i.e. wetter over the southern parts of the Maritime Continent, and drier over central and southern Philippines, as well as northern Borneo) is broadly aligned with the model predictions depicted in the subseasonal weather outlooks for the first and second fortnights of April 2020, apart from the anomalies over Mainland Southeast Asia.

Figure 1: Rainfall anomalies for the month of April 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).

1.2 Most parts of Southeast Asia south of 10°N experienced above-average temperature during April 2020 (Figure 2). The region between 10°N and 20°N experiences a range of below-average to above-average temperatures, while the northernmost parts of Southeast Asia (northern Myanmar, northern Lao PDR, and northern Viet Nam) experienced below-average temperature.

Figure 2: Temperature anomalies for the month of April 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) was active during April 2020. The MJO signal propagated eastwards from Phase 4 (Maritime Continent) to Phase 1 (Western Hemisphere) during the first two weeks of April. The MJO then stalled during the third week, before continuing to propagate eastward through Phases 2 and 3 (Indian Ocean) before reaching Phase 4 (Maritime Continent) at the end of the month. Typically for the region in April, Phases 7, 8, and 1 bring drier conditions, while Phases 3 to 5 bring wetter conditions, particularly in southern Southeast Asia.

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).

May 5, 2020

Review of Regional Haze Situation for April 2020

1.1 Northeast Monsoon conditions prevailed over most parts of the ASEAN region in April 2020. The prevailing winds blew mainly from the east or southeast over the eastern half of the Mekong sub-region, and from the southeast or south in the western half of the sub-region. In early April 2020, there was a gradual increase in shower activities over the eastern half of the sub-region. By the latter half of the month, an increase in shower activities were also observed over the western half of the sub-region. In the southern ASEAN region, scattered showers fell over most parts of the region. The prevailing winds blew mainly from the northeast or east over areas north of the equator and remain light and variable in direction over areas to the south.

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

1.2 In April 2020, hotspot activities continued to remain elevated in the Mekong sub-region, but the overall hotspot count was lower compared to that of past years. In the southern ASEAN region, the hotspot activities continued to remain subdued.

Figure 2: Hotspot count for the northern ASEAN region for Apr 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 Apr 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 April 2020, hotspot clusters were detected mostly in the northern Mekong sub-region, particularly in Myanmar and northern Lao PDR. These hotspot activities persisted for more than two to three weeks. Isolated hotspot activities were also detected in Cambodia and southern Lao PDR on many days. In the southern ASEAN region, isolated hotspots were detected on some days and were mostly short-lived.

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

1.4 In terms of fire intensity, the hotspot activities in northern Lao PDR, as well as in several parts of Myanmar recorded higher intensities as compared to other parts of the ASEAN region.

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

1.5 The smoke haze observed in the Mekong sub-region was less extensive in April 2020 as compared to March 2020. In April 2020, persistent smoke haze was observed mainly over the northern parts of the sub-region, particularly over Myanmar, northern Lao PDR, and northern and central Thailand. Over these areas, dense smoke haze was observed on many days during the first fortnight of the month, but an increase in shower activities brought a gradual improvement to the haze situation in the second half of the month. The air quality readings in northern and central Thailand improved from the Unhealthy to Very Unhealthy levels to the Excellent to Satisfactory levels by end-April 2020. Showers in the later part of the month had also brought an improvement to the haze situation in northeastern Cambodia and southern Lao PDR. In the southern ASEAN region, no significant smoke haze was observed except for localized smoke plumes emanating from some hotspots in Riau, Sumatra and the east coast of Peninsular Malaysia.

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 Apr 2020.