Monthly Archives: January 2024

January 19, 2024

Subseasonal Weather Outlook (22 January – 4 February 2024)

Issued: 19 January 2024
First forecast week: 22 January – 28 January 2024
Second forecast week: 29 January – 4 February 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over parts of the southeastern Maritime Continent during the next fortnight (22 January – 4 February).

Drier conditions are predicted over parts of the northeastern Maritime Continent in Week 1 (22 – 28 January). In Week 2 (29 January – 4 February), drier conditions are predicted over the western Maritime Continent.

Cooler than usual temperature is predicted over much of central and eastern Mainland Southeast Asia in Week 1 (22 – 28 January). Warmer that usual temperature is predicted over most of the Maritime Continent and the southern most parts of Mainland Southeast Asia in the next fortnight (22 January – 4 February).

A Madden-Julian Oscillation (MJO) signal was present over the Maritime Continent (Phase 4) in mid-January based on the RMM index. Most models predict this MJO signal to continue propagating eastwards through the Maritime Continent (Phase 5) and the Western Pacific (Phase 6) in Week 1. In Week 2, some models predict this signal to further propagate over the Western Pacific (Phase 7), whereas other models predict this signal to weaken and become inactive.

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.

January 15, 2024

Review of Regional Weather for December 2023

1. Overview

1.1 During December 2023, a mix of below- to above-average rainfall was recorded over the Maritime Continent (Figure 1). Near- to above-average rainfall was recorded over much of the western Maritime Continent and Borneo, with below- to near-average over much of the rest of the region. Over Mainland Southeast Asia, near-average rainfall was recorded for most of the region. The largest positive (wetter) anomalies for December were recorded over the Malay Peninsula and northern Sumatra 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 central Philippines (in both GSMaP-NRT and CMORPH-Blended), as well as Java and parts of Papua (CMORPH-blended only). The other notable difference between the two datasets was over central Viet Nam where CMORPH-Blended recorded above-average rainfall, while GSMAP-NRT recorded near average.

1.2 The observed rainfall anomaly pattern of above-average rainfall over the western Maritime Continent, below- to near- average rainfall for the rest of the Maritime Continent, and near-average over Mainland Southeast Asia, is broadly consistent with the predictions from the subseasonal weather outlooks for December 2023 (27 November – 10 December 2023, 11 – 24 December 2023 and 25 December 2023 – 7 January 2024).

Figure 1: Rainfall anomalies for December 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 Southeast Asia in December 2023 (Figure 2). The warmest anomalies (more than 2°C above average) were recorded over parts of Mainland Southeast Asia, including parts of Myanmar and northwestern Thailand.

Figure 2: Temperature anomalies for December 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 A Madden-Julian Oscillation (MJO) signal was present over the Indian Ocean (Phase 3) at the start of December 2023 (Figure 3). This signal propagated eastwards during December, weakening temporarily as it moved through the Western Pacific (Phases 6 and 7) and Western Hemisphere (Phase 8) towards the middle of the month. By the end of December, the MJO signal had strengthened again and returned to the Indian Ocean (Phase 2). Considering the phases with the stronger MJO signal (based on the RMM index), typically for this time of year, Phases 4 and 5 bring wetter conditions for most of the ASEAN region whereas Phases 1 and 2 bring drier conditions to the eastern Maritime Continent, with Phase 2 also bringing wetter conditions to the western 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 December 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. The positive Indian Ocean Dipole started to weaken in December. El Niño events tend to bring drier and warmer-than-average conditions to much of the Maritime Continent during December – February. Positive Indian Ocean Dipole events also tend to bring drier conditions to most of the southern half of the Maritime Continent during this period.

January 8, 2024

Review of Regional Haze Situation for December 2023

1.1 In December 2023, the prevailing winds over areas north of the Equator in the ASEAN region blew mostly from the northeast or east while the prevailing winds over areas south of the Equator were predominantly light and variable in direction (Figure 1). This signalled the establishment of Northeast Monsoon conditions over the ASEAN region. At times during the month, the northeasterly winds strengthened over parts of the Mekong sub-region and the South China Sea as well as over Peninsular Malaysia and Singapore, and brought periods of widespread rainfall associated with the monsoon surge.

1.2 Dry conditions were observed over the Mekong sub-region except for the coastal areas in the southern parts of Viet Nam where some showers occurred (Figure 1). The Alert Level 1 for the onset of the dry season for the northern ASEAN region was issued on the 14 December 2023. Rainfall was recorded over the rest of the ASEAN region except for the northern and the central parts of the Philippines where conditions were dry. Rainfall was noticeably higher over the eastern coastal areas of Peninsular Malaysia, southern parts of Thailand and the northern parts of Sabah, East Malaysia partly due to the occurrence of the monsoon surge (Figure 1). During the monsoon surge that occurred towards the end of the month, floods and landslides were reported which resulted in fatalities, displacement of people from homes and infrastructure damages in Peninsular Malaysia and the southern parts of Thailand. Higher rainfall amounts were also observed over Mindanao region, Philippines (Figure 1) partly due to the influence of Tropical Storm Jelawat which passed through the island between 17 and 19 December 2023, causing floods in the region.

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

1.3 The overall hotspot counts for the southern ASEAN region were mostly higher in December 2023 compared to previous years, particularly in Kalimantan and Sumatra as well as Sabah and Sarawak (Figure 2). In the northern ASEAN region, the hotspot counts were comparable to previous years (Figure 3).

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

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

1.4 Isolated to scattered hotspots were detected in the Mekong sub-region (Figure 4). While most of the hotspots were short-lived, some were persistent and intense. Clusters of hotspots were observed in the southern parts of Myanmar as well as the southwestern and eastern parts of Cambodia (Figure 4 and 5). A few persistent hotspots were also detected in parts of Thailand (Figure 4). A localised moderate smoke plume was observed to emanate from the hotspots detected in the southwestern parts of Cambodia on a few days (Figure 6 and 7)

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

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

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

Figure 7: A moderate smoke plume was observed in the southwestern parts of Cambodia on 20 December 2023. (Source: NOAA-20 satellite surveillance)

January 5, 2024

Subseasonal Weather Outlook (8 – 21 January 2024)

Issued: 5 January 2024
First forecast week: 8 January – 14 January 2024
Second forecast week: 15 January – 21 January 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over much of the southern ASEAN region in the next fortnight (8 – 21 January).

Drier conditions are predicted over parts of eastern Mainland Southeast Asia, as well as the Philippines and the surrounding region in Week 1 (8 – 14 January).

Warmer than usual temperature is predicted over much of the northern ASEAN region, as well as over the southern Maritime Continent in the next fortnight (8 – 21 January).

A Madden-Julian Oscillation (MJO) signal was present over the Indian Ocean (Phases 2 and 3) at the start of January. Most models predict this MJO signal to continue propagating eastwards through Phase 3 in Week 1 and then the Maritime Continent (Phases 4 and 5) during Week 2.