Monthly Archives: December 2022

December 23, 2022

Subseasonal Weather Outlook (26 December 2022 – 8 January 2023)

Issued: 23 December 2022
First forecast week: 26 December 2022 – 1 January 2023
Second forecast week: 2 January 2023 – 8 January 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are expected over the southern Maritime Continent in Week 1 (26 December 2022 – 1 January 2023). Wetter conditions are also predicted over parts of the northeastern Maritime Continent in the next fortnight (26 December 2022 – 8 January 2023), extending to southeastern Mainland Southeast Asia in Week 2 (2 – 8 January 2023). Drier conditions are predicted over the western Maritime Continent and the equatorial region in Week 1.

Cooler than usual temperature is predicted over much of central and eastern Mainland Southeast Asia in the next fortnight (26 December 2022 – 8 January 2023). Cooler conditions are also expected over much of the western and southern Maritime Continent in the next fortnight. Warmer than usual temperature is predicted over parts of the eastern equatorial region in Week 1 (26 December 2022 – 1 January 2023).

In the third week of December, a weak Madden-Julian Oscillation (MJO) signal was present over the Maritime Continent (Phases 4 and 5) based on the RMM index. Most models predict this MJO signal to propagate eastwards to the Western Pacific (Phase 6) in Week 1. There is a disagreement between the models for the MJO signal to either decay or continue propagating eastwards 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.

December 15, 2022

Review of Regional Haze Situation for November 2022

1.1 The inter-monsoon conditions gradually made way for the Northeast Monsoon over the ASEAN region in November 2022. The prevailing low-level winds over the northern ASEAN region blew from the northeast to east while the winds over most parts of the southern ASEAN region were light and variable in direction (Figure 1).

1.2 Most of the ASEAN region experienced wet weather conditions during November 2022, except for the northern, western and central parts of the Mekong sub-region where the conditions were relatively drier. Over the northern ASEAN region, rainfall amount was higher over the southern Mekong sub-region, coastal areas of Viet Nam and the Philippines. Widespread rainfall fell over much of the southern ASEAN region (Figure 1).

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

1.3 For November 2022, overall hotspot activities were mostly subdued due to the prevailing rainy conditions over the ASEAN region. Majority of the hotspots in the northern ASEAN region were detected in Myanmar, but the hotspot counts for the whole ASEAN region were generally lower or comparable to the counts in previous years (Figures 2 and 3).

Figure 2: Hotspot counts for the northern ASEAN region for the month of November (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 November (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 Throughout the November review period, few to isolated hotspots were detected in the ASEAN region. While these hotspots were mostly short-lived, hotspots were relatively more persistent in the southern parts of Myanmar, central and northern Viet Nam, as well as central Thailand (Figure 4). On most days, no discernable smoke plumes were observed.

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

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

1.5 The fire intensity of hotspots detected over the ASEAN region was generally low in November 2022 (Figure 5). No significant smoke haze was observed from satellite imagery.

Events – Start of Dry Season for the Northern ASEAN region – 2022

MEDIA RELEASE

START OF DRY SEASON FOR THE NORTHERN ASEAN REGION

Singapore, 15 December 2022 – According to the ASEAN Specialised Meteorological Centre (ASMC), the Northeast Monsoon season has become established over the ASEAN region in the past few weeks. This signals the onset of the traditional dry season in the northern ASEAN region¹, which is likely to extend into May 2023. During this period, prolonged dry weather can be expected as the monsoon rainband moves south of the Equator and dry northeasterly winds blow from continental Asia over the northern ASEAN region.

2 The prevailing La Niña conditions in the equatorial Pacific Ocean are expected to weaken and turn neutral by early 2023. The ongoing negative phase of the Indian Ocean Dipole (IOD) is also forecast to transition to a neutral phase by end of 2022². The return to neutral phase does not mean that weather conditions will necessarily be near their long-term average. Based on seasonal forecasts for the December 2022 to March 2023 period, the northern and western parts of the Mekong sub-region are expected to experience below-average rainfall, while near- to above-average rainfall is forecast for most other parts of the northern ASEAN region.

3 During this traditional dry season, fire hotspots and smoke haze may develop during extended periods of dry and warm weather, especially in parts of the Mekong sub-region where below-average rainfall is forecast. During the Northeast Monsoon, the low-level winds in the region typically blow from the northeast or east and transboundary haze may occur if the winds blow any smoke haze from fires to neighbouring countries. Early precautionary and mitigation measures are advised to prevent the occurrence of transboundary haze in the region.

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 northern ASEAN region comprises of Cambodia, Lao PDR, Myanmar, the Philippines, Thailand and Viet Nam.
[2] Both La Niña and negative IOD events tend to bring wetter conditions to most parts of the ASEAN region.

– End –

Alert20221215 – Start of Dry Season for the Northern ASEAN Region

Start of Dry Season for the Northern ASEAN Region

Over the past week, periods of dry weather were observed over many parts of the northern ASEAN region. Based on surveillance by the NOAA-20 satellite, a total of 96, 136 and 155 hotspots were detected in Thailand, Myanmar and Cambodia, respectively, between 8 and 14 Dec 2022.

With drier conditions expected to prevail over much of the northern ASEAN region in the coming weeks, increased hotspot activity and smoke haze development can be expected. The traditional dry season is expected to persist until April/May 2023.

ASMC Media Release – Start of Dry Season for the Northern ASEAN Region

Review of Regional Weather for November 2022

1. Overview

1.1 During November 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 southern and northeastern Mainland Southeast Asia where a mix of below- to above-average rainfall was recorded (Figure 1). The largest positive anomalies (wetter conditions) were recorded over southern Mainland Southeast Asia and central Borneo, for the GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates datasets respectively. The largest negative anomalies (drier conditions) were recorded over central Sumatra and northern half of the Philippines, 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 southern Mainland Southeast Asia are broadly consistent with the predictions from the subseasonal weather outlooks for November 2022 (31 October – 13 November, 14 – 27 November and 28 November – 11 December), although the wetter condition over central Borneo was not included in any of the outlooks.

Figure 1: Rainfall anomalies for November 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 most of Southeast Asia north of 10°N, except for some northwesternmost parts of Mainland Southeast Asia where below- to near-average temperatures are observed. In contrast, below- to near-average temperatures were recorded for most of the regions south of 10°N during November 2022 (Figure 2), except for south-eastern parts of the Maritime Continent where above-average temperatures are observed. The warmest anomalies were recorded around northern Viet Nam, with the coolest anomalies over central parts of Java islands.

Figure 2: Temperature anomalies for November 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 was present over the Western Pacific and the Western Hemisphere (Phases 7 and 8) in the first week of November, however it weakened and became indiscernible by the second week, based on the RMM Index (Figure 3). At the beginning of the third week, an MJO signal emerged over the Maritime Continent (Phase 4), which strengthened and propagated eastwards towards the Western Pacific (Phase 7), before becoming weak again at the end of the month. Typically, during this time of the year, Phase 6 tends to bring wetter conditions for eastern Maritime Continent while Phases 7 and 8 tends to bring drier conditions for the western Maritime Continent. Also for November, Phases 4 and 5 bring wetter conditions to much of the Southeast Asia. Therefore, the MJO may have contributed to the wetter conditions over southern coastal parts of Mainland Southeast Asia and southeastern Maritime Continent region in November 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. La Niña events tend to bring wetter-than-average conditions to much of Southeast Asia during the September to November period. Over the Indian Ocean, a negative Indian Ocean Dipole (IOD) was present and showing signs of weakening. Negative IOD tends to bring wetter-than-average conditions for much of Southeast Asia.

December 9, 2022

Subseasonal Weather Outlook (12 – 25 December 2022)

Issued: 9 December 2022
First forecast week: 12 December – 18 December
Second forecast week: 19 December – 25 December

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over parts of the western Maritime Continent in the next fortnight (12 – 25 December). Wetter conditions are also predicted over the northeastern Maritime Continent in Week 2 (19 – 25 December).

Cooler than usual temperature is expected in Week 1 (12 – 18 December) over much of central and eastern Mainland Southeast Asia and the western Maritime Continent. In Week 2 (19 – 25 December), these cooler conditions are predicted to ease over eastern Mainland Southeast Asia and persist elsewhere. Warmer than usual temperature is predicted over much of Myanmar in the next fortnight (12 – 25 December).

No discernible Madden-Julian Oscillation (MJO) signal was present in the first week of December based on the RMM index. There is disagreement between the models regarding MJO development, although most models predict any MJO signal to be weak and stay within the unit circle in the RMM diagram 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.