Monthly Archives: November 2023

November 30, 2023

21st ASEAN COF (Nov 2023, Online)

Twentieth Session of the ASEAN Climate Outlook Forum (ASEANCOF-21)

17, 20, 21, 23 Nov 2023, MSS

Consensus Bulletin for December-January-February (DJF) 2023-2024 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’s 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 Association of Southeast Asian Nations (ASEAN) region through pooling the expertise of ASEAN National Meteorological and Hydrological Services (NMHSs). In 2021, the ASEANCOF Working Group was established with the goal to guide and support the long-term development of ASEANCOF, in particular with regard to the implementation of objective outlooks.

The Twenty-First session of ASEANCOF (ASEANCOF-21) was organised by Meteorological Service Singapore (MSS) in collaboration with ASMC and the ASEANCOF Working Group. ASEANCOF-21 marked 10 years since the first ASEANCOF was held in December 2013. Participants from the NMHSs of ASEAN Member States created a consensus forecast for the boreal winter monsoon 2023/2024 in the ASEAN region. The consensus for the December-January-February (DJF) 2023/2024 outlook was achieved through an online session, which included presentations from different NMHSs, questionnaires, and discussions regarding the current climate conditions and predictions for Southeast Asia. The theme of ASEANCOF-21 was ‘The Future of Climate Services in Southeast Asia’’. On the last day of ASEANCOF-21, a sharing session was held which included presentations on the review of 10 years of ASEANCOF, Pilot Hydrological Outlook Forum, and WISER Asia Pacific project.

Conditions and Outlook

Recent analysis of sea surface temperature (SST) anomalies over the equatorial Pacific shows well above-average SSTs over the Nino3.4 region, along with atmospheric indicators such as trade wind strength and cloudiness, indicating El Niño conditions. In the Indian Ocean, a positive Indian Ocean Dipole is present.

For DJF 2023/2024, the current El Niño conditions are likely to continue. After DJF 2023/2024, global climate models predict the El Niño conditions to gradually weaken, though continue to indicate El Niño conditions for much of the first half of 2024. The peak strength of the ongoing El Niño, based on Nino3.4 index, is predicted to be moderate to strong.

The positive IOD is predicted to weaken and return to IOD-neutral over DJF 2023/2024.

The onset of the Northeast monsoon season has been or is expected to be later than average for much of Mainland Southeast Asia, with near or later than average over some parts of the Maritime Continent. The strength of the Northeast monsoon is expected to be weaker than normal over most of the Southeast Asia, based on model predictions and supported by the ongoing El Niño conditions.

During DJF 2023/2024, tropical cyclone frequency is predicted to be below average around the Philippine Sea and the Bay of Bengal, and below to near average around South China Sea.

Taking into consideration the national level forecasts, the present state of the climate, and the forecasts available from the GPCs, ASEANCOF-21 agreed on the following consensus-based outlook for DJF 2023-24 over the ASEAN region:

RAINFALL

Over much of the Maritime Continent, below- to near-normal rainfall is predicted, apart from over the equatorial region, where a mix of below- to above-normal rainfall is predicted.

For Mainland Southeast Asia, a mix of near- to above-normal rainfall is predicted. Near- to above-normal rainfall is predicted over parts of northern and central Mainland Southeast Asia, while below- to near-normal rainfall is predicted mainly over western parts. Elsewhere over this region, near-normal rainfall is predicted.

TEMPERATURE

Near- to above-normal temperature is predicted over Southeast Asia. While above-normal temperature is predicted for most of the region, near-normal temperature is predicted over parts of northern and western Myanmar, and near- to above-normal temperature is predicted over parts of Lao PDR, Viet Nam, and the 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 boreal (Northern Hemisphere) summer monsoon outlook and further updates on the national scale, the relevant NMHSs should be consulted (see Annex C).

Consensus Maps for DJF 2023/2024 Season

The following maps provide the probabilistic outlooks for DJF 2023/2024 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-21 Outlook Bulletin

Acknowledgements

ASEANCOF would like to convey its appreciation to the NMHSs of the ASEAN Member States for sharing their national level forecasts, the GPCs, the Southeast Asia Regional Climate Centre – Network, RIMES, UN ESCAP, and other partners of ASEANCOF for sharing their products and expertise, and the World Meteorological Organization Regional Office in Asia and the Southwest Pacific (WMO-RAP) for their continued support of ASEANCOF.

November 24, 2023

Subseasonal Weather Outlook (27 November – 10 December 2023)

Issued: 24 November 2023
First forecast week: 27 November – 3 December 2023
Second forecast week: 4 December – 10 December 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over parts of southern Mainland Southeast Asia and the northern Malay Peninsula in the next fortnight (27 November – 10 December). Also, wetter conditions are predicted over much of the central and southeastern Maritime Continent in the next fortnight.

Warmer than usual temperature is predicted over most of the Maritime Continent and eastern coast of Mainland Southeast Asia during the next fortnight (27 November – 10 December).

A Madden-Julian Oscillation (MJO) signal has been present over the Western Hemisphere and Africa (Phases 8 and 1) since mid-November. Models predict the MJO signal to propagate eastwards, reaching the Indian Ocean (Phase 2) by the start of the forecast period. Most models predict the signal to weaken in Phase 3 during the first 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.

November 14, 2023

Alert20231114 – End of Dry Season for the Southern ASEAN Region

End of Dry Season for the southern ASEAN region

In recent days, widespread shower activities have helped to further suppress the overall hotspot and smoke haze situation over the southern ASEAN region. Based on surveillance by the NOAA-20 satellite, 18 and 36 hotspots were detected in Sumatra on 12 and 13 November 2023 respectively, and 3 hotspots were detected in Kalimantan on both days.

The hotspot and haze situation over the southern ASEAN region is expected to remain subdued as shower activities are forecast to continue in the coming months. However, isolated hotspots and localised smoke plumes may still develop in fire-prone areas during brief periods of relatively drier weather.

Review of Regional Weather for October 2023

1. Overview

1.1 During October 2023, a mix of below- to above-average rainfall was recorded over Southeast Asia (Figure 1). Over much of Mainland Southeast Asia, near- to above-average rainfall was recorded. Over much of the Maritime Continent, below-average rainfall was recorded. For Southeast Asia, the largest positive (wetter) anomalies were recorded over central Viet Nam based on GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates. In contrast, the largest negative (drier) anomalies were recorded over Sumatra and the Philippines (in both GSMaP-NRT and CMORPH-Blended).

1.2 The observed rainfall anomaly pattern of above-average rainfall over much of Mainland Southeast Asia and below-average rainfall over the Maritime Continent are broadly consistent with the predictions from the subseasonal weather outlooks for October 2023 (2 – 15 October 2023 and 16 – 29 October 2023).

Figure 1: Rainfall anomalies for October 2023 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2022. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Above-average temperatures were recorded over the Maritime continent and much of Mainland Southeast Asia (Figure 2). The warmest anomalies (more than 2°C above average) were recorded over southern Sumatra.

Figure 2: Temperature anomalies for October 2023 based on ERA-5 reanalysis. The climatological reference period is 2001-2022. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 No active Madden-Julian Oscillation (MJO) was observed for much of October 2023. An MJO was present in the Maritime Continent (Phase 5) on the first two days of November before decaying. There were signs of an MJO signal developing over the Western Pacific and Western Hemisphere (Phases 7 and 8) in the fourth week. Typically for October, Phase 7 tends to bring drier conditions to the western Maritime Continent and Phase 8 tends to bring drier conditions to much of the Maritime Continent.

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 El Niño conditions persisted over the equatorial Pacific during October 2023. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) continue to show El Niño conditions, with key atmospheric indicators (cloudiness and trade winds) also supporting these conditions. A positive Indian Ocean Dipole is also present. El Niño events tend to bring drier and warmer-than-average conditions to much of the Maritime Continent during September to November. Positive Indian Ocean Dipole events also tend to bring drier conditions to most of the southern half of the Maritime Continent during this period.

November 10, 2023

Subseasonal Weather Outlook (13 – 26 November 2023)

Issued: 10 November 2023
First forecast week: 13 November – 19 November 2023
Second forecast week: 20 November – 26 November 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For the southern ASEAN region in the next fortnight (13 – 26 November), drier conditions are predicted, except over parts of the equatorial region where wetter conditions are predicted.

For the northern ASEAN region in Week 1 (13 – 19 November), wetter conditions are predicted over much of this region. In Week 2 (20 – 26 November), drier conditions are predicted over southern Mainland Southeast Asia.

Warmer than usual temperature is predicted over most of the Maritime Continent during the next fortnight (13 – 26 November).

No Madden-Julian Oscillation (MJO) signal was present around the start of the forecast period. Most models predict an MJO signal to develop over the Western Pacific (Phase 7) in Week 1 and then propagate to the Western Hemisphere and Africa (Phases 8 and 1).

November 3, 2023

Review of Regional Haze Situation for October 2023

1.1 The Southwest Monsoon gradually transitioned into inter-monsoon conditions from the end of October 2023. As the monsoon rainband moved towards the Equator, the prevailing winds weakened and turned light and variable over the equatorial regions (Figure 1). During the first week of October, Typhoon Koinu (Figure 9) brought about heavy rainfall and strong winds over parts of the northern Philippines.

1.2 Dry weather persisted over much of the southern ASEAN region for the first half of October, with moderate to dense haze observed mainly over southern and central Sumatra, as well as southern and central Kalimantan (Figure 6). Towards the end of October, there was an increase in showers over parts of southern Kalimantan and southern Sumatra, which helped to improve the hotpot and haze situation (Figure 1). On 24 October 2023, the ASMC Alert Level for the southern ASEAN region was downgraded to Alert Level 1 as the risk of transboundary haze subsided. Over the northern ASEAN region, wet weather prevailed, and the overall haze situation was subdued in the region (Figure 1).

Figure 1: Average Daily Rainfall and Mean Winds for October 2023. (Source: JAXA GsMaP and GFS, respectively)

1.3 Over the southern ASEAN region, the hotspot counts in October 2023 were mostly higher compared to previous years, especially over Sumatra and Kalimantan where there was a significant rise in hotspot activity with the highest count recorded in five years (Figure 2). Over the Mekong sub-region, the overall hotspot count in October 2023 was mostly comparable to or lower than in previous years (Figure 3).

Figure 2: Hotspot counts for the southern ASEAN region for October (2019-2023) based on NOAA-20 satellite surveillance.

Figure 3: Hotspot counts for the northern ASEAN region for October (2019-2023) based on NOAA-20 satellite surveillance.

1.4 In October, hotspot activities were persistent in parts of central and southern Sumatra, southern and central Kalimantan, as well as parts of the Lesser Sunda Islands and Sulawesi (Figure 4). The fire intensity was highest for parts of southern Sumatra and Kalimantan (Figure 5). Moderate to dense smoke haze was observed in central and southern Sumatra, as well as southern and eastern Kalimantan on many days this month (Figures 6, 7 and 8). Lighter smoke haze drifted under prevailing winds to affect parts of Peninsular Malaysia and Singapore in early October 2023.

Figure 4: Distribution of hotspots detected in October 2023 based on NOAA-20 satellite surveillance.

Figure 5: Maximum fire intensity in October 2023 based on NOAA-20 satellite surveillance.

Figure 6: Number of days with moderate to dense smoke haze observed in October 2023 based on satellite imagery, ground observations, and air quality reports.

Figure 7: Moderate to dense smoke haze was observed in southern and eastern Kalimantan on 3 October 2023. (Source: Himawari-9 satellite surveillance)

Figure 8: Moderate to dense smoke haze was observed in parts of central and southern Sumatra on 16 October 2023. (Source: Himawari-9 satellite surveillance)

Figure 9: Typhoon Koinu over the western Pacific Ocean on 4 October 2023. (Source: MODIS satellite surveillance)