Monthly Archives: January 2023

January 27, 2023

Alert20230127 – Activation of Alert Level 2 for the Mekong Sub-region

Activation of Alert Level 2 for the Mekong Sub-region

In recent days, prevailing dry weather conditions over the Mekong sub-region have resulted in an increase in hotspot activities. Based on satellite surveillance, moderate smoke haze was observed to emit from clusters of hotspots detected in the northern and eastern parts of Cambodia, as well as northern parts of Myanmar. Isolated hotspots with smoke plumes were also detected elsewhere in the Mekong sub-region. A total of 757 and 403 hotspots were detected in the Mekong sub-region on 25 and 26 January 2023 respectively from the NOAA-20 satellite.

Dry weather conditions are forecast to continue over the Mekong sub-region in the coming weeks, with prevailing winds likely to blow from the northeast or east. Under these conditions, the hotspot and smoke haze situation could worsen with an increased risk of transboundary smoke haze development.

January 20, 2023

Subseasonal Weather Outlook (23 January – 5 February 2023)

Issued: 20 January 2023
First forecast week: 23 January 2023 – 29 January 2023
Second forecast week: 30 January 2023 – 5 February 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over much of the Maritime Continent and coastal parts of eastern Mainland Southeast Asia in the next fortnight (23 January – 5 February). The highest likelihood of wetter conditions is over the region between 0° and 10°N, including the Malay Peninsula, northern Borneo, and the southern Philippines, in Week 1 (23 – 29 January).

Cooler than usual temperature is predicted over much of the southern half of the ASEAN region in Week 1 (23 – 29 January), generally in line with the predicted wetter conditions.

No clear Madden-Julian Oscillation (MJO) signal was present during the third week of January. Some models predict an MJO signal to develop and propagate eastward over the Indian Ocean (Phases 2 and 3) during the forecast period.

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 12, 2023

Review of Regional Weather for December 2022

1. Overview

1.1 During December 2022, a mix of below- to above-average rainfall was recorded over the Maritime Continent, while near-average rainfall was recorded over much of Mainland Southeast Asia, except for coastal parts of eastern Mainland Southeast Asia where above-average rainfall was recorded (Figure 1). The largest positive anomalies (wetter conditions) were recorded over northwestern Continent, including Malay Peninsula for both the GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates. The largest negative anomalies (drier conditions) were recorded over the southern Borneo, with CMORPH-Blended data showing relatively drier anomalies as compared to GSMaP-NRT data.

1.2 The observed rainfall anomaly pattern of a mix of below- to above-average rainfall for the Maritime Continent and the above-average rainfall for eastern Mainland Southeast Asia are broadly consistent with the predictions from the subseasonal weather outlooks for December 2022 (28 November – 11 December 2022, 12 – 25 December 2022 and 26 December 2022 – 8 January 2023).

Figure 1: Rainfall anomalies for December 2022 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2021. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Warmer-than-average temperatures were recorded over northwestern Mainland Southeast Asia and parts of southeastern Maritime Continent, whereas below- to near-average temperatures were observed elsewhere over the ASEAN region. The warmest anomalies were recorded over Myanmar and the coolest over the eastern Mainland Southeast Asia.

Figure 2: Temperature anomalies for December 2022 based on ERA-5 reanalysis. The climatological reference period is 2001-2021. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 An Madden-Julian Oscillation (MJO) signal emerged over the Indian Ocean (Phase 3) and the Maritime Continent (Phase 4) at the end of the first week of December, based on the RMM index (Figure 3). This signal weakened and went inside the RMM unit circle at the end of the second week of December. At the end of the third week, an MJO signal reappeared over the Maritime Continent (Phases 4 & 5), which strengthened and propagated eastwards towards the Western Pacific (Phase 6) over the last week of December. Typically, during this time of the year, Phases 4 and 5 bring wetter conditions for most of the ASEAN region whereas Phase 6 tends to bring wetter conditions for eastern Maritime Continent. Therefore, the MJO may have contributed to the wetter conditions over northern parts of the Maritime Continent region December 2022.

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 La Niña conditions were present over the tropical Pacific. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric indicators over the tropical Pacific Ocean were consistent with La Niña conditions, though there are signs of weakening. La Niña events tend to bring wetter-than-average conditions to much of Southeast Asia during the September to November period.

January 11, 2023

Review of Regional Haze Situation for December 2022

1.1 In December 2022, the Northeast Monsoon was well established over the ASEAN region as the predominant low-level winds blew from the northeast over areas north of the Equator and blew from the west or northwest over areas south of the Equator. The northeasterly winds strengthened at times, bringing a monsoon surge over the South China Sea and parts of the Mekong sub-region (Figure 1).

1.2 During the month, dry conditions were experienced over most parts of the Mekong sub-region except for the southeastern parts of the sub-region where some rainfall was observed. Alert Level 1 for the onset of the dry season in the northern ASEAN region was issued on the 15 December 2022. Wet weather was experienced elsewhere in the ASEAN region with the highest rainfall observed over the eastern parts of the Peninsular Malaysia and the southern parts of Thailand and the Philippines (Figure 1), under the influence of the monsoon surge. Floods and landslides were also reported in these areas on several days during the month which resulted in several fatalities and displacement of people from their homes.

Figure 1: Average Daily Rainfall and Mean Winds for December 2022. (Source: JAXA GsMaP and GFS, respectively)

1.3 1.3 There was an increase in the overall hotspot activities in the Mekong sub-region following the onset of the dry conditions over the sub-region in December 2022 with the highest hotspot activity detected in Cambodia (Figure 2). In the southern ASEAN region, hotspot activities were mostly subdued due to the prevailing wet weather (Figure 3). While the hotspot activities in ASEAN region were mostly comparable to the same month in previous years, there was a noticeable increase in the hotspot activities in Cambodia compared to the last two years.

Figure 2: Hotspot counts for the northern ASEAN region for the month of December (2018 – 2022). [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2018 are based on the Suomi-NPP satellite.]

Figure 3: Hotspot counts for the southern ASEAN region for the month of December (2018 – 2022). [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2018 are based on the Suomi-NPP satellite.]

1.4 In the northern ASEAN region, isolated to scattered hotspots were detected mostly in the Mekong sub-region. The hotspots were more persistent in the northern and eastern parts of Cambodia, the southern parts of Myanmar, the northern parts of Viet Nam and the northern and central parts of Thailand (Figure 4). While the overall fire intensity of hotspots was low, localised smoke plumes were observed to emanate from hotspots in the eastern parts of Cambodia and northern parts of Viet Nam where the fire intensity was slightly higher (Figure 5). In the southern ASEAN region, hotspot activities were subdued due to the wet weather with few hotspots detected in Sumatra, Kalimantan and Sulawesi.

Figure 4: Distribution of hotspots detected in December 2022 based on NOAA-20 satellite surveillance.

Figure 5: Maximum fire intensity in December 2022 based on NOAA-20 satellite surveillance.

January 6, 2023

Subseasonal Weather Outlook (9 – 22 January 2023)

Issued: 6 January 2023
First forecast week: 9 January 2023 – 15 January 2023
Second forecast week: 16 January 2023 – 22 January 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over much of southeastern Mainland Southeast Asia and the Philippines in the next fortnight (9 – 22 January). Wetter conditions are also predicted to develop over the western Maritime Continent in Week 2 (16 – 22 January).

Drier conditions are predicted over parts of the southern Maritime Continent in Week 1 (9 – 15 January).

Warmer than usual temperature is predicted around central and northeastern Mainland Southeast Asia in Week 1 (9 – 15 January).

A Madden-Julian Oscillation (MJO) signal weakened over the Western Pacific (Phase 7) at the start of January. Most models predict this MJO signal to strengthen again as the signal propagates eastward over the Western Hemisphere and Africa (Phases 8 and 1) during Week 1, and reaching the Indian Ocean (Phases 2 and 3) during Week 2.