Monthly Archives: May 2022

May 27, 2022

Subseasonal Weather Outlook (30 May – 12 June 2022)

Issued: 27 May 2022
First forecast week: 30 May – 5 June
Second forecast week: 6 June – 12 June

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For rainfall, wetter conditions are expected over the southern Maritime Continent in the next fortnight (30 May – 12 June). Drier conditions are expected over much of the eastern half of the equatorial region in Week 1 (30 May – 5 June). In Week 2 (6 June – 12 June), drier conditions are expected over southeastern Mainland Southeast Asia.

For temperature, warmer than usual temperatures are predicted over the southeastern Maritime Continent in Week 1 (30 May – 5 June). These warmer conditions may ease in Week 2 (6 June – 12 June). Cooler than usual temperatures are expected over southern Mainland Southeast Asia and parts of the Philippines in Week 1.

There was no Madden-Julian Oscillation (MJO) signal present towards the end of May based on the RMM index. An MJO signal is expected to emerge over the Western Pacific (Phases 6 and 7) and then propagate to the Western Hemisphere and Africa (Phase 8) in Week 1. Most models predict the MJO signal to decay in Week 2.

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.

May 19, 2022

Alert20220519 – End of Dry Season for the Northern ASEAN Region

End of Dry Season for the Northern ASEAN Region

Over the past week, there have been widespread shower activities over much of the Mekong sub-region. The wet weather has helped to subdue the overall hotspot activity and no significant smoke haze was observed in recent days. The total hotspot count in the sub-region also remained low, with a total of 8 and 1 hotspots detected in the Mekong sub-region on 17 and 18 May 2022, respectively, from the NOAA-20 satellite surveillance.

With rainy weather forecast to persist over the northern ASEAN region in the coming days, hotspot and smoke haze activity is expected to remain generally subdued.

May 17, 2022

Review of Regional Weather for April 2022

1. Overview

1.1 During April 2022, near- to above-average rainfall was recorded over much of the northern ASEAN region, while a mix of below- to above-average rainfall was recorded over the southern ASEAN region (Figure 1). For the northern ASEAN region, the largest positive anomalies (wetter conditions) were recorded over the Philippines for both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended), which partly was associated with Tropical Storm Megi during the middle of April. For the southern ASEAN region, negative anomalies (drier conditions) were recorded over the eastern parts. Elsewhere in the southern ASEAN region, rainfall tended to be a mix of below- to above-average. There are some discrepancies between the two datasets, as GSMaP-NRT recorded a mix of below- to above-average rainfall for much of southern Sumatra and Borneo, while CMORPH-Blended recorded below- to near-average rainfall with isolated areas of above-average rainfall over the mentioned regions.

1.2 The observed rainfall anomaly pattern of above-average rainfall for parts of the northern ASEAN region, including the Philippines and a mix of below- to above-average rainfall for the southern ASEAN region is broadly consistent with the predictions from the subseasonal weather outlooks for April 2022 (4 – 17 April, and 18 April – 1 May).

Figure 1: Rainfall anomalies for the month of April 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 Most parts of northern ASEAN region recorded below-average temperature in April 2022 (Figure 2). The largest negative anomalies (less than 1°C cooler) were over northeastern Thailand, Lao PDR, and Viet Nam. Elsewhere, there was near- to above-average temperature, with most of the regions recording above-average temperature south of the equator.

Figure 2: Temperature anomalies for the month of April 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 The Madden-Julian Oscillation (MJO) signal was weak or indiscernible for much of April 2022, based on the MJO phase diagram below (Figure 3). At the start of the month, the MJO was indiscernible. In the second week of April, there were signs of eastward progression of a signal, however, this signal was weak and remained inside the unit circle. Around the middle of April, the signal strengthened slightly, moving outside the unit circle in the Western Hemisphere (Phase 8) before becoming indiscernible again by the third week in April as it moved towards the Indian Ocean (Phase2). Phase 8 tends to bring drier conditions to much of the Maritime Continent, while Phase 1 tends to bring drier conditions only to parts of the eastern Maritime Continent. Therefore, the MJO may have contributed to the drier conditions in the April in the southeastern 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 Over the tropical Pacific Ocean, La Niña conditions were present. 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. La Niña events tend to bring wetter-than-average conditions to much of Southeast Asia during the March to May period.

Review of Regional Haze Situation for April 2022

1.1 The Northeast Monsoon gradually transitioned to inter-monsoon conditions in April 2022 as the monsoon rainband moved northwards over the equator. The prevailing winds over most parts of the ASEAN region were light and variable in direction on most days, except for the Philippines where winds blew mostly from the northeast or east (Figure 1).

1.2 Most parts of the Mekong sub-region experienced prolonged dry weather in April 2022, except for southern Cambodia and northern Myanmar where showers were observed on some days. Rainy weather conditions were observed elsewhere in the ASEAN region on most days during this period, although drier conditions prevailed over northern Philippines and the Lesser Sunda Islands. Heavy rainfall was observed in parts of central and southern Philippines, contributed by the passage of Tropical Storm Megi in the second week of April 2022 (Figure 1).

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

1.3 For April 2022, the total number of hotspots were lower or comparable to previous years for the same period (Figures 2 and 3), except for Lao PDR where significantly higher numbers of hotspots were detected in April 2022 compared to previous years. Slightly more hotspots were detected in Sumatra compared to previous years.

Figure 2: Hotspot counts for the northern ASEAN region for the month of April (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 April (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 Under the prevailing dry weather in April 2022, scattered to widespread hotspots were detected in most parts of the Mekong sub-region on many days. In particular, persistent clusters of high intensity hotspots, were detected in northern and central Lao PDR, as well as western and northeastern Myanmar during the month (Figures 4 and 5). Widespread moderate to dense smoke haze was observed to emanate from these hotspots on several days in early to mid- April, with transboundary haze observed to drift from Lao PDR into Thailand, Viet Nam and Cambodia on several days (Figures 6 and 7). As a result, Alert Level 3 was issued on 11 April 2022. As shower activities returned later in the month, the overall hotspot and smoke haze situation improved and a downgrade to Alert Level 2 was issued on 29 April 2022.

1.5 The hotspot and smoke haze situation in the southern ASEAN region remained comparatively subdued as rainy conditions prevailed. Isolated hotspots were detected and localised smoke plumes were observed to emanate from some of these hotspots in West Kalimantan and the western coastal areas of central Sumatra on some days (Figure 8).

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

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

Figure 6: Number of days with moderate to dense smoke haze observed in April 2022 based on satellite imagery, ground observations, and air quality reports.

Figure 7: Moderate to dense smoke haze was observed over western and central
Myanmar, as well as over Lao PDR drifting into Thailand, Viet Nam and Cambodia (right).

Figure 8: Localised smoke plumes were observed to emanate from isolated hotspots in West Kalimantan (left) and the western coast of Central Sumatra (right) on some days.

May 13, 2022

Subseasonal Weather Outlook (16 – 29 May 2022)

Issued: 13 May 2022
First forecast week: 16 May – 22 May
Second forecast week: 23 May – 29 May

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are expected over much of Mainland Southeast Asia in the next fortnight (16 – 29 May). The highest likelihood of wetter conditions is over parts of Myanmar and Thailand in Week 1 (16 – 22 May). Wetter conditions are also expected over much of the northern half of the Philippines in Week 1.

Drier conditions are expected to develop over much of the equatorial region in the next fortnight (16 – 29 May). In Week 1 (16 – 22 May), drier conditions are expected in the western Maritime Continent and easternmost part of the equatorial region. In Week 2 (23 – 29 May), these drier conditions are predicted to extend to cover most of the equatorial region.

Cooler temperatures than usual are expected over most of Mainland Southeast Asia in the next fortnight (16 May – 29 May) with the highest likelihood over northeastern Mainland Southeast Asia.

Warmer than usual temperatures are predicted over the western half of the equatorial region over the next fortnight (16 May – 29 May).

A weak Madden-Julian Oscillation (MJO) signal was present over the Indian Ocean (Phases 2 and 3) in the beginning of May. Models predict the MJO signal to be over the Western Pacific (Phase 7) at the start of forecast period. This signal is predicted to decay over the Western Hemisphere and Africa (Phase 8) during Week 1.

May 10, 2022

Alert20220510 – Downgrade to Alert Level 1 for the Mekong Sub-Region

Downgrade to Alert Level 1 for the Mekong Sub-Region

In recent days, shower activities have increased over the Mekong sub-region. The showers have helped to improve the overall hotspot and haze situation, with localised hotspots and smoke haze observed over some parts of Myanmar, northern Thailand, and northern Lao PDR. With rainy weather forecast to continue in the coming days, the hotspot and haze situation over the Mekong sub-region is expected to improve further.

The hotspot count over the Mekong sub-region continued to be on a declining trend, with a total of 183 and 39 hotspots detected on 7 and 8 May 2022 respectively, from the surveillance by the NOAA-20 satellite.