Monthly Archives: January 2022

January 21, 2022

Subseasonal Weather Outlook (24 January – 6 February 2022)

Issued 21 January 2022
First forecast week: 24 January – 30 January
Second forecast week: 31 January – 6 February

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

In Week 1 (24 – 30 January), drier conditions are predicted over much of the western and southern Maritime Continent. Also in Week 1, wetter conditions are predicted over northeastern parts of the Maritime Continent (in particular for the Philippines).

For temperature, warmer than usual conditions are predicted for much of the central part of Southeast Asia (central and eastern Mainland Southeast Asia, the western half of the Maritime Continent) and the northern Philippines in Week 1 (24 – 30 January). In Week 2 (31 January – 6 February), these warmer conditions are expected to ease, apart from over the coastal regions of eastern Mainland Southeast Asia.

Cooler than usual conditions are predicted for northwestern Mainland Southeast Asia in the next fortnight (24 January – 6 February).

By the middle of January, the previous Madden-Julian Oscillation (MJO) signal had decayed. Most models predict no significant MJO activity 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 20, 2022

Review of Regional Haze Situation for December 2021

1.1 By December 2021, Northeast Monsoon conditions had become fully established over the ASEAN region. The prevailing low-level winds over regions north of the equator blew mostly from the north or northeast while the winds over regions south of the equator blew mainly from the west or northwest. Alert Level 1 for the Mekong sub-region was issued on 7 December 2021, indicating the start of the dry season. Persistent dry conditions were observed over the sub-region in December 2021. Higher rainfall was observed over the rest of the ASEAN region, particularly over Peninsular Malaysia and the southern Philippines, which were affected by heavy rainfall in December 2021 (Figure 1). In particular, Super Typhoon Rai made landfall over the southern Philippines on December 16, 2021 and caused severe damage, flooding and loss of lives. Floods also affected several Malaysian states including Pahang, Melaka, Negri Sembilan and Johor in the second half of December, resulting in significant damage and casualties.

Figure 1: Average Daily Rainfall and Mean Wind for December 2021. (Source: JAXA GsMaP and GFS respectively)

1.2 For the December 2021 review period, overall hotspot activities started to increase in the Mekong sub-region following the onset of dry conditions, while wet conditions continued to subdue hotspot activities in the southern ASEAN region. The hotspot counts for the Mekong sub-region in December 2021 were mostly lower compared to previous years, while the hotspot counts over the southern ASEAN region were generally comparable to those in previous years (Figures 2 and 3).

Figure 2: Hotspot counts for the northern ASEAN region for the month of December (2017 – 2021). [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2017 – 2018 are based on the Suomi-NPP satellite.]

Figure 3: Hotspot counts for the southern ASEAN region for the month of December (2017 – 2021). [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2017 – 2018 are based on the Suomi-NPP satellite.]

1.3 During the review period, isolated to scattered hotspots were detected throughout the Mekong sub-region and isolated smoke plumes were sometimes observed to emanate from the detected hotspots. Although isolated hotspots were detected in Sumatra, parts of Peninsular Malaysia and Kalimantan, the hotspot activities were generally subdued over the southern ASEAN region (Figures 4 and 5).

Figure 4: Distribution of hotspots detected in December 2021 based on NOAA-20 satellite surveillance.

Figure 5: Maximum fire intensity in December 2021 based on NOAA-20 satellite surveillance.

January 13, 2022

Review of Regional Weather for December 2021

1. Overview

1.1 During December 2021, coastal central parts of Viet Nam, Peninsular Malaysia and southern half of the Philippines experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded over the central Philippines and the Peninsular Malaysia (due to Super Typhoon Rai and Tropical Depression 29W respectively, which made landfall in mid-December), for both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). For the rest of the Mainland Southeast Asia, rainfall anomalies were negligible, as expected at the start of dry season for the northern ASEAN region. A mix of above- and below-average rainfall was experienced for most regions in the equatorial region. There is some discrepancy between the two satellite datasets for the below-average rainfall for central parts of Borneo, with more extensive drier conditions based on CMORPH-Blended (Figure 1, right) compared to near- to above-average rainfall for GSMaP-NRT (Figure 1, left). Elsewhere in the southern Maritime Continent, wetter-than-average rainfall conditions were recorded over much of the land masses.

1.2 The observed large-scale rainfall anomaly pattern (i.e. above-average rainfall in regions linked to tropical storm and cyclone activity and below-average rainfall over parts of equatorial region) is broadly consistent with the predictions from the subseasonal weather outlooks for December 2021 (29 November – 12 December, 13 – 26 December, and 27 December – 9 January), apart from the positive anomalies (wetter conditions) for Peninsular Malaysia not highlighted in the outlooks.

Figure 1: Rainfall anomalies for the month of December 2021 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2020. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Below-average temperatures were recorded over central and eastern regions of Mainland Southeast Asia in December 2021 (Figure 2). In contrast, above-average temperatures (more than 1°C warmer) were recorded over parts of Myanmar. Elsewhere, near- to slightly above-average temperature were recorded.

Figure 2: Temperature anomalies for the month of December 2021 based on ERA-5 reanalysis. The climatological reference period is 2001-2020. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 A Madden-Julian Oscillation (MJO) was present over the Western Pacific (Phase 6) at the start of December 2021, based on the MJO phase diagram below (Figure 3). From second week of December onwards, this signal was not very coherent (very slow eastwards propagation towards Phase 7) and likely influenced by the background La Niña conditions. Phase 6 tends to bring wetter conditions to eastern Maritime Continent, while Phase 7 tends to bring drier conditions to the western Maritime Continent at this time of the year.

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 the Maritime Continent during the December to February period.

January 7, 2022

Subseasonal Weather Outlook (10 – 23 January 2022)

Issued 7 January 2022
First forecast week: 10 January – 16 January
Second forecast week: 17 January – 23 January

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted in the next fortnight (10 – 23 January) over a band that includes the Malay Peninsula, southern Viet Nam, and much of the northern Philippines and surrounding area.

Wetter conditions are predicted in Week 1 (10 – 16 January) over central parts of the Maritime Continent (in particular for western Borneo and Java). These wetter conditions are expected to ease in Week 2 (17 – 23 January), although there is a chance that they remain over the region around Java. Also in Week 2, wetter conditions are predicted to develop over parts of the central and southern Philippines.

No significant regional temperature anomalies are expected in the next fortnight (10 – 23 January).

Based on the RMM index, a Madden-Julian Oscillation (MJO) signal was present over the Western Pacific (Phase 7) at the start of January, although the signal has been less coherent in part due to the background La Niña state. As with the previous outlook, while some models predict this signal to propagate slowly eastwards, others predict the signal to decay in Phase 7.