Monthly Archives: April 2023

April 28, 2023

Subseasonal Weather Outlook (1 – 14 May 2023)

Issued: 28 April 2023
First forecast week: 1 May 2023 – 7 May 2023
Second forecast week: 8 May 2023 – 14 May 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

In Week 1 (1 – 7 May), drier conditions are predicted over much of central and eastern Mainland Southeast Asia, as well as northern parts of the Philippines. Also in Week 1, wetter conditions are predicted over much of the Maritime Continent.

Warmer than usual temperature is predicted over much of the eastern half of the Maritime Continent during the next fortnight (1 – 14 May). Warmer than usual temperature is also predicted over much of Mainland Southeast Asia in Week 1 (1 – 7 May).

A Madden-Julian Oscillation (MJO) signal was present over the Indian Ocean (Phase 2) at the end of April. Most models predict an MJO signal to continue propagating eastwards reaching the Western Pacific (Phases 6 and 7) in Week 2 (8 – 14 May).

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.

April 24, 2023

Alert20230424 – Downgrade to Alert Level 2 for the Mekong Sub-Region

Downgrade to Alert Level 2 for the Mekong Sub-Region

In recent days, increased rainfall has helped to improve the overall hotspot and smoke haze situation over the Mekong sub-region. This has helped to reduce the extent of transboundary smoke haze in the sub-region, although elevated hotspot and smoke haze activity is still expected mainly in the drier areas of the northern and western sub-region.

A total of 919 and 676 hotspots were detected in the Mekong sub-region on 22 and 23 April 2023 respectively from the NOAA-20 satellite. As more rainfall is forecast in the coming weeks, the hotspot and haze situation over the sub-region is expected to further improve.

April 14, 2023

Subseasonal Weather Outlook (17 – 30 April 2023)

Issued: 14 April 2023
First forecast week: 17 April 2023 – 23 April 2023
Second forecast week: 24 April 2023 – 30 April 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

In Week 1 (17 – 23 April), drier conditions are predicted over much of Mainland Southeast Asia, the Malay Peninsula and parts of the central Maritime Continent.

Warmer than usual temperature is predicted over much of Mainland Southeast Asia and the Malay Peninsula in Week 1 (17 – 23 April), in line with the predicted drier conditions over these regions.

A Madden-Julian Oscillation (MJO) signal was present over the Western Pacific (Phases 6 and 7) in the second week of April. Most models predict this MJO signal to continue propagating eastwards before decaying over the Western Hemisphere and Africa (Phase 1) towards the end of the forecast period.

April 13, 2023

Review of Regional Weather for March 2023

1. Overview

1.1 During March 2023, a mix of below- to above-average rainfall was recorded over much of the Maritime Continent. Parts of the northern Maritime Continent, including Philippines and northeastern Borneo, received below- to near-average rainfall, while parts of the equatorial region received above-average rainfall. Over Mainland Southeast Asia, near-average rainfall was recorded over most of northwestern and eastern region, and below-normal elsewhere. The largest positive anomalies (wetter conditions) were recorded over the central parts of Borneo 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 in both CMORPH-Blended data and GSMaP-NRT data.

1.2 The observed rainfall anomaly pattern of a mix of below- to above-average rainfall for the Maritime Continent and below- to near-average rainfall for Mainland Southeast Asia are broadly consistent with the predictions from the subseasonal weather outlooks for March 2023 (6 – 19 March 2023 and 20 March – 2 April 2023).

Figure 1: Rainfall anomalies for March 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 Below- to near-average temperatures were recorded over much of the western and central Maritime Continent, with above-average temperatures over parts of the eastern Maritime Continent. A mix of below- to above-average temperatures were recorded over the northern and central Mainland Southeast Asia and predominantly below-average temperatures were observed over southeastern Mainland Southeast Asia. The warmest anomalies were recorded over northern Viet Nam, and the coolest over the southeastern Mainland Southeast Asia.

Figure 2: Temperature anomalies for March 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 Western Pacific (Phase 6) at the start of March. This MJO signal propagated eastwards and strengthened as it passed through the Western Pacific (Phase 7) and Western Hemisphere (Phases 8 and 1) in the first half of March. In the second half of March, this signal relatively weakened and continued propagating eastwards through the Western Pacific (Phase 1) and Indian Ocean (Phases 2 and 3). The MJO signal weakened at the end of month and became indiscernible over the Maritime Continent (Phase 4), based on the RMM Index. Typically, during this time of the year, Phase 6 tends to bring wetter conditions to eastern Maritime Continent, while 7 and 8 tends to bring drier conditions to much of the Maritime Continent. Phases 1 and 2 tends to bring drier conditions over the eastern Maritime Continent, whereas Phase 3 tends to bring wetter conditions to the western Maritime Continent. Phase 4 usually brings wetter 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 La Niña conditions have now ended, and the tropical Pacific is now in an ENSO neutral state. Overall, sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric and oceanic indicators over the tropical Pacific Ocean, indicate neutral conditions.

April 6, 2023

Review of Regional Haze Situation for March 2023

1.1 In March 2023, the ASEAN region continued to experience Northeast Monsoon conditions. Over areas north of the equator, the prevailing winds blew mainly from the northeast although light and variable winds prevailed over most parts of the Mekong sub-region. The prevailing winds over areas south of the Equator blew mostly from the west or northwest. As the Northeast monsoon conditions gradually weakened in the last week of the month, the prevailing winds over most of the ASEAN region started to turn light and variable on several days. (Figure 1).

1.2 The dry conditions over the Mekong sub-region and northern Philippines persisted throughout the review period of March 2023, except for isolated shower activities in some parts of the sub-region on a few days. Elsewhere in the ASEAN region, generally wet conditions were observed in many areas. (Figure 1).

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

1.3 For March 2023, the hotspot counts in the Mekong sub-region were higher or comparable to previous years under extended dry conditions, leading to an increase in overall hotspot activity (Figure 2). In particular, the highest hotspot activity was detected in Lao PDR, and the hotspot counts for 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 March (2019 – 2023) based on NOAA-20 satellite surveillance.

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

1.4 Scattered to widespread hotspots were detected in the Mekong sub-region during the continued dry weather conditions. Clusters of hotspots were more intense and persistent in eastern and central Myanmar, Lao PDR, northern Thailand, and northeastern Cambodia. 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 March 2023 based on NOAA-20 satellite surveillance.

1.5 The overall fire intensity in the Mekong sub-region had increased in March 2023, particularly over the fire-prone areas in Lao PDR, eastern and central Myanmar. (Figure 5). Widespread transboundary moderate to dense smoke haze was observed in the vicinity of the hotspot clusters in eastern Myanmar, northern and central Thailand, Lao PDR and northern Cambodia (Figure 6, 7 and 8) on many days. With the deteriorating hotspots and haze situation, Alert Level 3 was issued for the Mekong sub-region on 2 Mar 2023. Localised smoke plumes and occasional hazy conditions were also observed in northern Viet Nam on some days.

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

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

Figure 7: Moderate to dense smoke haze emanated from the hotspot clusters detected in northeastern Cambodia and southern Lao PDR on 8 March 2023, based on NOAA-20 satellite observation.

Figure 8: Moderate to dense smoke haze observed over eastern Myanmar, northern Thailand, and northern Lao PDR on 23 March 2023, based on NOAA-20 satellite surveillance.