Monthly Archives: March 2023

March 31, 2023

Subseasonal Weather Outlook (3 – 16 April 2023)

Issued: 31 March 2023
First forecast week: 3 April 2023 – 9 April 2023
Second forecast week: 10 April 2023 – 16 April 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are expected over much of Mainland Southeast Asia in Week 1 (3 – 9 April), in particular over central parts of Mainland Southeast Asia. Drier conditions are also predicted over parts of the western and central Maritime Continent in Week 2 (10 – 16 April).

Warmer than usual temperature is predicted over much of Mainland Southeast Asia in Week 1 (3 – 9 April), in line with the predicted drier conditions. These warmer conditions are predicted to persist over central Mainland Southeast Asia and gradually ease elsewhere in Week 2 (10 – 16 April).

No discernible Madden-Julian Oscillation (MJO) signal was present at the end of March. Most models predict an MJO signal to emerge in the Western Pacific (Phases 6 and 7) during Week 1 and then slowly propagate eastwards over the rest of the forecast period. However, some models predict no discernible MJO signal during this time.

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.

March 28, 2023

ASMC Climate Bulletin (Mar 2023)

March 17, 2023

Subseasonal Weather Outlook (20 March – 2 April 2023)

Issued: 17 March 2023
First forecast week: 20 March 2023 – 26 March 2023
Second forecast week: 27 March 2023 – 2 April 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are expected over much of the northern ASEAN region in Week 1 (20 – 26 March), in particular over central and eastern Mainland Southeast Asia and northern Philippines. These drier conditions are predicted to persist over these regions and extend further southwards to the Malay Peninsula in Week 2 (27 March – 2 April).

Warmer than usual temperature is expected over central and eastern Mainland Southeast Asia and northern Philippines in the next fortnight (20 March – 2 April), in line with the predicted drier conditions.

A Madden-Julian Oscillation (MJO) signal was present over the Western Hemisphere and Africa (Phases 8 and 1) in the middle of March. Models predict this signal to weaken and continue propagating eastwards to the Indian Ocean (Phase 2), and decay by the end of Week 1.

March 16, 2023

Review of Regional Weather for February 2023

1. Overview

1.1 During February 2023, a mix of below- to above-average rainfall was recorded over the Maritime Continent. The northern half of the Maritime Continent received predominantly near- to above-average rainfall, and the southern half received predominantly below-average rainfall although some above-average rainfall was recorded in the southern most parts (Figure 1). Over Mainland Southeast Asia, near-average rainfall was recorded over most of region. The largest positive anomalies (wetter conditions) were recorded over the 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 parts of southern Sumatra and Sulawesi, 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 (with much of above-average rainfall in the northern Maritime Continent and below-average rainfall in the southern part) and near-average rainfall for Mainland Southeast Asia are broadly consistent with the predictions from the subseasonal weather outlooks for February 2023 (6 – 19 February 2023 and 20 February – 5 March 2023).

Figure 1: Rainfall anomalies for February 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 Warmer-than-average temperatures were recorded over northern Mainland Southeast Asia and parts of eastern Maritime Continent. Near- to below-average temperatures were observed over parts of southern Mainland Southeast Asia and around the Malay Peninsula. Elsewhere in the ASEAN region, near-average temperatures were observed. The warmest anomalies were recorded over northern Myanmar and northern Viet Nam, and the coolest over the southeastern Mainland Southeast Asia.

Figure 2: Temperature anomalies for February 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 February. This MJO signal propagated eastwards through the Maritime Continent (Phases 4 and 5) in the first half of February and reached the Western Pacific (Phases 6 and 7) by the end of Week 2. The signal continued propagating eastwards before weakening from the middle of Week 3 over the Western Pacific (Phase 7) and becoming indiscernible at the end of the month, based on the RMM Index. Typically, during this time of the year, Phase 3 tends to bring wetter conditions to the western Maritime Continent, Phases 4 and 5 tends to bring wetter conditions to the Maritime Continent. Phase 6 tends to bring wetter conditions to eastern Maritime Continent while 7 tends to bring drier 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 La Niña conditions were present over the tropical Pacific but have weakened since December 2022. Although overall, sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric indicators over the tropical Pacific Ocean, continued to indicate La Niña conditions. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during the December to February period.

March 8, 2023

Review of Regional Haze Situation for February 2023

1.1 The ASEAN region continued to experience Northeast Monsoon conditions in February 2023. Over areas north of the equator, the prevailing winds blew mainly from the northeast even though the winds were mostly light and variable in direction over the Mekong sub-region. For areas south of the equator, the prevailing winds blew mostly from the west or northwest (Figure 1).

1.2 Dry conditions persisted over the Mekong sub-region throughout the review period of February 2023, except for isolated shower activities in the southern parts of the sub-region on some days. Elsewhere in the ASEAN region, rainy weather was observed in many areas. However, parts of Peninsular Malaysia and the northern Philippines experienced brief periods of drier weather. (Figure 1).

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

1.3 Prolonged dry conditions over the Mekong sub-region led to an increase in overall hotspot activity in February 2023 and the hotspot counts in the Mekong sub-region were higher or comparable to previous years (Figure 2). In particular, the highest hotspot activity was detected in Myanmar, and the hotspot counts for both Myanmar and Lao PDR were the highest in 5 years. For the southern ASEAN region, hotspot activity remained generally subdued and the hotspot counts were generally lower than in previous years (Figure 3).

Figure 2: Hotspot counts for the northern ASEAN region for the month of February (2019 – 2023) based on NOAA-20 satellite surveillance.

Figure 3: Hotspot counts for the southern ASEAN region for the month of February (2019 – 2023) based on NOAA-20 satellite surveillance.

1.4 Hotspot activity was widespread and persistent over the Mekong sub-region during the review period of February 2023. On many days, clusters of hotspots were detected in parts of Lao PDR, northern and eastern Cambodia, northern and central Myanmar, and northern Thailand. Isolated hotspots were also detected in northern Viet Nam. Over the southern ASEAN region, few hotspot activities were detected but most of them was short-lived (Figure 4).

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

1.5 The overall fire intensity in the Mekong sub-region had increased in February 2023, particularly over the fire-prone areas in Lao PDR, northern and central Myanmar, northern and eastern Cambodia, and northern Thailand (Figure 5). As a result, moderate to dense smoke haze was observed in the vicinity of the hotspot clusters in Myanmar, Thailand, and Cambodia (Figure 6, 7, 8 and 9) on many days. Localised smoke plumes and occasional hazy conditions were also observed in northern Viet Nam on some days.

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

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

Figure 7: Moderate to dense smoke haze observed over northern and central Myanmar on 24 February 2023, based on NOAA-20 satellite surveillance.

Figure 8: Moderate to dense smoke haze emanated from the hotspot clusters detected in northern and central Thailand on 24 February 2023, based on NOAA-20 satellite observation.

Figure 9: Moderate smoke haze emanated from the hotspot clusters detected in northern and eastern Cambodia on 20 February 2023, based on NOAA-20 satellite observation.

March 3, 2023

Subseasonal Weather Outlook (6 – 19 March 2023)

Issued: 3 March 2023
First forecast week: 6 March 2023 – 12 March 2023
Second forecast week: 13 March 2023 – 19 March 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are expected over the southern Maritime Continent in the next fortnight (6 – 19 March). Drier conditions are also expected over southern Mainland Southeast Asia in Week 1 (6 – 12 March).

Wetter conditions are expected over much of the western Maritime Continent in Week 1 (6 – 12 March) and much of the northeastern Maritime Continent in Week 2 (13 – 19 March).

Cooler than usual temperature are predicted over much of the ASEAN region in the next fortnight (6 – 19 March), in particular over southern Mainland Southeast Asia, the western and central Maritime Continent and parts of the Philippines.

No clear Madden-Julian Oscillation (MJO) signal was present at the end of February. Models predict an MJO signal to emerge over the Western Pacific (Phases 6 and 7) by Week 1 and propagate eastwards over the Western Hemisphere and Africa (Phases 8 and 1) during the forecast period.

March 2, 2023

Alert20230302 – Activation of Alert Level 3 for the Mekong Sub-region

Activation of Alert Level 3 for the Mekong Sub-region

In the past few days, persistent dry weather over the Mekong sub-region has led to an escalation in the hotspot and haze situation there. Based on NOAA-20 satellite surveillance, a total of 1180 and 1636 hotspots were detected in the Mekong sub-region on 28 Feb 2023 and 1 Mar 2023 respectively.

The current dry conditions are expected to persist in the coming days, with the prevailing winds forecast to blow from the northeast. Under these conditions, the elevated hotspot activity and widespread hazy conditions in the Mekong sub-region are likely to continue, with a high risk of transboundary haze occurrence in the sub-region.

ASMC Media Release – Deteriorating haze conditions in the Mekong sub-region

Events – Deteriorating haze conditions in the Mekong sub-region – 2023

MEDIA RELEASE

WIDESPREAD SMOKE HAZE IN THE MEKONG SUB-REGION UNDER PREVAILING DRY WEATHER

Singapore, 2 March 2023 – The ASEAN Specialised Meteorological Centre (ASMC) has raised the Alert Level for early warning of transboundary smoke haze in the Mekong sub-region1 to the highest level (Alert Level 3) on 2 March 2023. With persistent dry weather conditions expected, there may be a worsening in transboundary smoke haze situation in the coming weeks.

2 Hotspot and smoke haze activities in the Mekong sub-region have escalated since the start of the northern ASEAN dry season in December 2022. Based on NOAA-202 satellite surveillance, a total of 1180 and 1636 hotspots were detected in the Mekong sub-region on 28 February 2023 and 1 March 2023 respectively. Widespread moderate to dense smoke haze was observed over northern Lao PDR, northern and central parts of Thailand, as well as central and southern parts of Myanmar in the past few days. Many air quality stations in the central and northern Mekong sub-region also reported air quality at the unhealthy to very unhealthy levels.

3 The prevailing low-level winds in the Mekong sub-region are forecast to continue blowing from the northeast in the coming days, which will contribute to a high risk of transboundary haze occurrence. Existing La Niña3 conditions in the equatorial Pacific Ocean are likely to weaken to neutral in March or April 2023. Although near-to-above normal rainfall is predicted for the Mekong sub-region in the coming months, prolonged dry periods are still expected, and the hotspot and smoke haze situation is likely to stay elevated till the end of the traditional dry season in May 2023.

4 For regular and ad-hoc updates of the regional weather and smoke haze situation and early warnings, please visit the ASMC website at https://asmc.asean.org.

[1] The Mekong sub-region comprises of Cambodia, Lao PDR, Myanmar, Thailand and Vietnam.
[2] The National Oceanic and Atmospheric Administration-20 (NOAA-20) satellite monitors global environmental conditions and collects and disseminates data related to weather, land and oceans.
[3] La Niña conditions tend to bring wetter conditions to most parts of the ASEAN region.

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