Monthly Archives: December 2020

December 24, 2020

Subseasonal Weather Outlook (28 December 2020 – 10 January 2021)

Issued 24 December 2020
First forecast week: 28 December – 3 January
Second forecast week: 4 January – 10 January

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For the next fortnight (28 December 2020 – 10 January 2021), an increased chance of wetter conditions is predicted over parts of northern ASEAN region, in particular the Philippines, northern Borneo, southern Viet Nam, Cambodia, southern Thailand and Peninsular Malaysia. A lower increase in likelihood of wetter conditions is also predicted around the southeastern part of the Maritime Continent in the second week (4 – 10 January 2021).

An increased chance of cooler conditions is predicted over most of Mainland Southeast Asia in the next fortnight (28 December 2020 – 10 January 2021).

The Madden-Julian Oscillation (MJO) signal is becoming indiscernible over the Western Pacific (Phase 6). Some dynamical models predict the MJO to re-emerge over the Indian Ocean in early January 2021, propagating eastwards towards the Maritime Continent 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.

December 21, 2020

Review of Regional Haze Situation for November 2020

1.1 Intermonsoon conditions over the ASEAN region gradually made way for the Northeast Monsoon in November 2020. The prevailing winds blew from the northeast or east over the northern ASEAN region and were light and variable over the southern ASEAN region. In the northern ASEAN region, dry weather prevailed over most of the Mekong sub-region except for the coastal regions of southern Viet Nam where higher rainfall was observed partly due to Super Typhoon Goni. The average daily rainfall (Figure 1) was highest in the Philippines under the influence of Tropical Storm Etau, Typhoon Vamco and Super Typhoon Goni. Wet weather prevailed over most parts of the southern ASEAN region as the monsoon band moved south towards the equator.

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

1.2 Due to drier conditions over parts of Kalimantan, Myanmar and Thailand, hotspot counts in these regions were slightly elevated compared to the same review period in 2016 – 2018 but lower than those in 2019. Elsewhere over the ASEAN region, the hotspot counts were comparable to those in previous years’ review periods (Figures 2 and 3).

Figure 2: Hotspot counts for the southern ASEAN region for the month of November between 2016 and 2020. [Note: The hotspot counts from 2019 onwards 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 the month of November between 2016 and 2020. [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2016-2018 are based on the Suomi-NPP satellite.]

1.3 In November 2020, Isolated hotspots were detected in many parts of the ASEAN region, particularly in Kalimantan, the Lesser Sunda Islands, Sulawesi, and the Mekong sub-region (Figure 4). On a few days in November 2020, localised smoke plumes were observed to emanate from some of the hotspots in Kalimantan, Sulawesi, and the Myanmar. Otherwise, no significant smoke haze was observed.

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

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

December 15, 2020

Review of Regional Weather for November 2020

1. Overview

1.1 During November 2020, much of the eastern parts of Mainland Southeast Asia and the Philippines experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded over northern Philippines and central and southern Viet Nam based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended), linked to the tropical storms and cyclones in the first half of November 2020 (including Tropical Cyclone Goni, Tropical Storm Atsani, and Tropical Cyclone Vamco). Elsewhere in Mainland Southeast Asia, near-average rainfall was experienced in much of the region. A mix of above- and below-average rainfall was experienced for most regions in the equatorial region and south of the equator, with the largest region of above-average rainfall in the western Maritime Continent.

1.2 The observed large-scale rainfall anomaly pattern (i.e. above-average rainfall in regions linked to tropical storm and cyclone activity) is broadly consistent with the predictions from the subseasonal weather outlooks for November 2020 (2 – 15 Nov, 16 – 29 Nov).

Figure 1: Rainfall anomalies for the month of November 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 Colder-than-average temperatures were recorded over some regions of the eastern half of Mainland Southeast Asia in November 2020 (Figure 2), in particular Cambodia. In contrast, warmer-than-average temperatures were recorded over northern Viet Nam and Lao PDR, northwestern Thailand and parts of Myanmar. Elsewhere, the temperature for November was closer to average.

Figure 2: Temperature anomalies for the month of November 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 Starting off as a weak signal in the Western Pacific (Phase 7), the Madden-Julian Oscillation (MJO) signal strengthened in the Western Hemisphere (phases 8 and 1) during the first half of November (Figure 3), and continued propagating eastward through the Indian Ocean (phases 2 and 3) in the second half and eventually weakened as it approached the Matitime Continent (Phase 4) at the end of the month. Phases 8 and 1 typically bring below-average rainfall for much of Southeast Asia during this time of the year, while Phases 2 and 3 tend to bring wetter conditions to parts of the western Maritime continent (observed in the rainfall anomalies for November 2020, Figure 1) and drier conditions to eastern parts.

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).

2.2 Over the tropical Pacific Ocean, La Niña conditions were present. The sea surface temperatures in the central and eastern Pacific Ocean continued to cool, with atmospheric indicators (cloudiness and wind anomalies) also remaining consistent with La Niña conditions. La Niña events tend to bring wetter-than-average conditions to much of Southeast Asia during the September to November period.

December 11, 2020

Subseasonal Weather Outlook (14 – 27 December 2020)

Issued 11 December 2020
First forecast week: 14 December – 20 December
Second forecast week: 21 December – 27 December

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For the next fortnight (14 – 27 December), an increased chance of wetter conditions is predicted over the Philippines, parts of central and southern Viet Nam, southern Thailand and southern Myanmar. An increased chance of wetter conditions is also predicted around the southeastern part of the Maritime Continent in the first week (14 – 20 December). Drier conditions are predicted over parts of the equatorial region, in particular Borneo and central Sumatra for the next fortnight (14 – 27 December).

There is an increased chance of cooler conditions over southern parts of Indonesia in the first week (14 – 20 December), easing in the second week (21 – 27 December).

A weak Madden-Julian Oscillation (MJO) signal is present over the eastern Maritime Continent (Phase 5). Most models predict this MJO to continue propagating slowly eastwards over the Pacific, although weakening due in part to the La Niña conditions.

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.

December 3, 2020

Alert20201203 – Start of Dry Season for the Northern ASEAN Region

Start of Dry Season for the Northern ASEAN Region

Over the past several days, dry weather has persisted over the northern ASEAN region, and this has contributed to an increase in hotspot activities. In particular, localised smoke plumes were observed to emanate from some of these hotspots in Thailand and Myanmar. Based on surveillance by the NOAA-20 satellite, 95 and 27 hotspots were detected in the northern ASEAN region on 1 and 2 December 2020 respectively.

The Northeast Monsoon is expected to last until March 2021. Extended periods of dry weather may lead to a further increase in hotspot activities in the northern ASEAN region over the next several months.

December 1, 2020

15th ASEAN COF (Nov 2020, Online)

Fifteenth Session of the ASEAN Climate Outlook Forum (ASEANCOF-15)

23, 25, 27 November 2020, Online

Consensus Bulletin for December-January-February (DJF) 2020/2021 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 fifteenth ASEANCOF (ASEANCOF-15) was organised by the ASEAN Specialised Meteorological Centre. Representatives from National Meteorological and Hydrological Services (NMHSs) of ASEAN Member States created a consensus forecast for the winter monsoon 2020/2021 in the ASEAN region. The consensus for December-January-February (DJF) 2020/2021 outlook 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 indicated below average SSTs across most of the central and eastern tropical Pacific Ocean and that La Niña conditions are present. The international climate outlooks predict La Niña conditions are very likely to continue during DJF 2020/2021. The La Niña conditions are expected to be moderate to strong during this time. La Niña conditions are expected to weaken during the boreal (Northern Hemisphere) spring.

The current Indian Ocean Dipole (IOD) state is neutral and is expected to remain neutral for DJF 2020/2021.

The Northeast (NE) Monsoon is expected to be stronger than normal, based on model predictions and supported by the current La Niña conditions. For most countries, the onset of the NE monsoon is expected to be near-normal, or slightly earlier.

Overall, the tropical cyclone frequency is expected to be above average for the Bay of Bengal, South China Sea and around the Philippine Sea. This is based on model predictions as well as during La Niña events there tends to be more tropical cyclones than average for the region.

Taking into consideration the national level forecasts, the present state of the climate, and the forecasts available from the GPCs and other global centres, the forum agreed on the following consensus-based outlook for DJF 2020/2021 for the Southeast Asia region:

RAINFALL

For the upcoming boreal (Northern Hemisphere) winter season (December- January- February 2020/2021), near-normal to above-normal rainfall is expected over much of the region (Brunei Darussalam, Malaysia, the Philippines, Singapore, Thailand, and southern parts of Myanmar and Viet Nam). The highest probabilities of above-normal rainfall are over Brunei Darussalam, southern Thailand, and parts of Malaysia and the Philippines. Elsewhere, near-normal or a range of below-normal to above-normal rainfall is predicted.

TEMPERATURE

For the southern half of Southeast Asia near-normal to above-normal temperature is predicted, including Brunei Darussalam, Malaysia, Singapore, and the southern half of the Philippines. In the northern half of Southeast Asia, near-normal to below-normal temperature is expected for parts of Lao PDR and Viet Nam. An increased chance of above-normal temperature is expected over northern Thailand and northern Lao PDR. Elsewhere, near-normal temperature is expected, particularly over most of Thailand, Myanmar and northern Philippines. On top of these temperature outlook, there may be increased chance of cold surges due to the stronger Northeast Monsoon predicted for the coming December-January-February 2020/2021 season.

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

Consensus Maps for DJF 2020/2021 Season

The following maps provide the probabilistic outlooks for DJF 2020/2021 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-15 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 and regional centres for sharing their products and expertise, and WMO for their continued support of ASEANCOF. The Forum would also like to thank the participants from the disaster risk reduction sector who attended the final day of the forum, sharing valuable insights into how to make seasonal outlooks more useful in the ASEAN region.