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.
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).
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)