Monthly Archives: September 2022

September 30, 2022

Subseasonal Weather Outlook (3 – 16 October 2022)

Issued: 30 September 2022
First forecast week: 3 October – 9 October
Second forecast week: 10 October – 16 October

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For rainfall, wetter conditions are predicted over most of the southern ASEAN region in the next fortnight (3 – 16 October). Drier conditions are predicted over the western Maritime Continent in Week 2 (10 – 16 October).

For temperature, cooler than usual temperature is predicted over much of the central Maritime Continent in line with the wetter conditions in the next fortnight (3 – 16 October).

No clear Madden-Julian Oscillation (MJO) signal was present at the end of September. Most models forecast an MJO signal to emerge over the Maritime Continent (Phases 4 and 5) in Week 1 and propagate eastwards towards the Western Pacific (Phase 6).

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.

September 28, 2022

ASMC Bulletin (Issue #10, Sep 2022)

September 16, 2022

Subseasonal Weather Outlook (19 September – 2 October 2022)

Issued: 16 September 2022
First forecast week: 19 September – 25 September
Second forecast week: 26 September – 2 October

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over most of the southern ASEAN region in the next fortnight (19 September – 2 October).

Drier conditions are predicted over parts of northeastern Mainland Southeast Asia in Week 1 (19 – 25 September). These drier conditions are predicted to spread, covering much of Mainland Southeast Asia in Week 2 (26 September – 2 October).

For temperature, cooler than usual temperature is predicted over parts of the central Maritime Continent in Week 1 (19 – 25 September). Warmer than usual temperature is predicted over parts of the southeastern Maritime Continent in the next fortnight (19 September – 2 October).

No clear Madden-Julian Oscillation (MJO) signal was present in the first half of September. Models predict no significant MJO activity over the forecast period.

September 15, 2022

Review of Regional Haze Situation for August 2022

1.1 The monsoon rainband remained north of the Equator in August 2022, as Southwest Monsoon conditions persisted over the ASEAN region. The prevailing low-level winds blew mainly from the east or southeast for areas south of the Equator and from the southeast or southwest over areas north of the Equator.

1.2 For the southern ASEAN region, shower activities were observed across many areas despite the ongoing traditional dry season. Rainfall was most intense in Luzon, Philippines contributed by Severe Tropical Storm Ma-on which made landfall on August 23, 2022. Persistent dry weather conditions developed in Java and the Lesser Sunda Islands during the month. In addition, intermittent periods of drier weather were observed in Sumatra, Borneo, Peninsular Malaysia and Singapore in early to mid-August. The traditional wet season for the northern ASEAN region persisted in August 2022 and shower activities were observed over the region on most days of the month (Figure 1).

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

1.3 There was an increase in hotspot activity in the southern ASEAN region during brief periods of drier weather in the first half of August 2022. For the northern ASEAN region, continued showers helped to keep the hotspot counts low. The hotspot count for most parts of the ASEAN region were comparable or lower to previous years, except for Kalimantan where hotspot counts were higher compared to 2020 and 2021 (Figure 2 and 3).

Figure 2: Hotspot counts for the southern ASEAN region for the month of August (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 northern ASEAN region for the month of August (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 4. Dry periods in early to mid-August 2022, contributed to an escalation in hotspot activity in the southern ASEAN region (Figure 4). In particular, clusters of hotspots with high intensity were detected in West Kalimantan on several days during this period. Increased hotspot activity was also detected in parts of Viet Nam and Sumatra. (Figure 5). Moderate smoke haze was observed in the vicinity of the hotspot clusters in West Kalimantan on several days in the first half of August 2022, but the haze was generally localized. (Figures 6 and 7).

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

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

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

Figure 7: Himawari-8 satellite imagery showing moderate smoke haze in the vicinity of clusters of hotspots located in West Kalimantan on 9 August 2022 (left) and 18 August 2022 (right).

Review of Regional Weather for August 2022

1. Overview

1.1 During August 2022, much of the ASEAN region experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded over the southern parts of Myanmar, western Borneo, and the Maluku Islands based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). In contrast to the above-average rainfall, parts of northern Myanmar, the Malay Peninsula, northern Borneo, the Philippines, and Papua experienced below- to near-average rainfall, or a mix of between above- and below-average rainfall. The two datasets agree well over most of the ASEAN region. However, there are some discrepancies over the Philippines and west Papua where GSMaP-NRT recorded near- to above-average rainfall whereas CMORPH-Blended recorded below- to near-average rainfall.

1.2 The observed rainfall anomaly pattern of above-average rainfall for much of the Maritime Continent region is broadly consistent with the predictions from the subseasonal weather outlooks for August 2022 (25 July – 7 August, 8 – 21 August and 22 August – 4 September). While overall for August much of Mainland Southeast Asia experienced above-average rainfall as well, the subseasonal outlooks predicted wetter conditions in the second week, and drier conditions towards the end of the month.

Figure 1: Rainfall anomalies for August 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 The northernmost and southernmost parts of the ASEAN region experienced above-average temperatures during August 2022, with below- to near-average temperatures elsewhere (Figure 2). The warmest anomalies were recorded over northern Myanmar and Papua, with the coolest anomalies over parts of Sumatra and Cambodia. Most of the cooler anomalies occurred for areas that also experienced above-average rainfall.

Figure 2: Temperature anomalies for August 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 There were some signs of a Madden-Julian Oscillation (MJO) signal over the Maritime Continent (Phases 4 and 5) in the first week of August, however there was no discernible signal by the second week, based on the RMM Index (Figure 3). An MJO signal emerged over the Indian Ocean (Phase 2) towards the end of August, its strength briefly amplifying at the start of the last week in August, before becoming weak again at the end of the month. Typically, Phase 2 tends to bring drier conditions over the northeastern ASEAN region and wetter conditions for the western Maritime continent at this time of year, while Phases 4 and 5 bring wetter conditions to northern parts of the Maritime Continent. Therefore, while there was little MJO activity for most of August, the MJO signals near the start and end of the month may have contributed to the wetter-than-average conditions.

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 remain consistent with La Niña conditions. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during the June to August period. Over the Indian Ocean, a negative Indian Ocean Dipole (IOD) was present. Negative IOD tends to bring wetter-than-average conditions for much of Southeast Asia.

September 2, 2022

Subseasonal Weather Outlook (5 – 18 September 2022)

Issued: 2 September 2022
First forecast week: 5 September – 11 September
Second forecast week: 12 September – 18 September

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over much of the southern Maritime Continent in the next fortnight (5 – 18 September). Wetter conditions are also expected in Week 1 (5 – 11 September) over much of southwestern Mainland Southeast Asia.

Drier conditions are expected over the westernmost part of the Maritime Continent in the next fortnight (5 – 18 September).

For temperature, cooler than usual temperature is predicted over parts of the central Maritime Continent in the next fortnight (5 – 18 September).

No clear Madden-Julian Oscillation (MJO) signal was present at the start of September. Most models predict little to no MJO activity over the forecast period, based on the RMM index.