Monthly Archives: August 2023

August 18, 2023

Subseasonal Weather Outlook (21 August – 3 September 2023)

Issued: 18 August 2023
First forecast week: 21 August – 27 August 2023
Second forecast week: 28 August – 3 September 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over parts of Mainland Southeast Asia and the Philippines in the next fortnight (21 August – 3 September).

Drier conditions are predicted over much of the central Maritime Continent in Week 1 (21 – 27 August). These drier conditions are predicted to extend eastward covering much of the southern half of the Maritime Continent in Week 2 (28 August – 3 September).

Warmer than usual temperature is predicted over much of the Maritime Continent in the next fortnight (21 August – 3 September), in line with the predicted drier conditions. Warmer than usual temperature is also predicted over much of northern Mainland Southeast Asia in the next fortnight.

No coherent Madden-Julian Oscillation (MJO) signal was present during the first half of August. During the forecast period, models predict no strong MJO signal, although a few models predict a weak MJO signal to develop over the Western Hemisphere and Africa (Phases 8 and 1) and then propagate eastwards.

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.

Review of Regional Weather for July 2023

1. Overview

1.1 During July 2023, a mix of below- to above-average rainfall was recorded over Southeast Asia. Over Mainland Southeast Asia, below-average rainfall was recorded over the northeastern parts of the region, while a mix of below- to above-average rainfall was recorded over the rest of the region. However, there was some discrepancy over Cambodia, with GSMaP-NRT indicating predominantly above-average rainfall, while CMORPH-Blended indicating well below-average rainfall. Over the Maritime Continent, above-average rainfall was recorded over much of the western half of the region, with below-average rainfall over much of the eastern half. The largest positive (wetter) anomalies were recorded over parts of southern Myanmar, southern Viet Nam, and northern Philippines for GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates. The largest negative (drier) anomalies were recorded over parts of Papua (CMORPH-Blended) and northern Viet Nam and coastal Myanmar (both GSMaP-NRT and CMORPH-Blended).

1.2 The observed rainfall anomaly pattern of a mix of below- to near-average rainfall over the ASEAN region is broadly consistent with the predictions from the subseasonal weather outlooks for July 2023 (26 June – 9 July 2023, 10 – 23 July 2023 and 24 July – 6 August 2023).

Figure 1: Rainfall anomalies for July 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 The observed rainfall anomaly pattern of a mix of below- to near-average rainfall over the ASEAN region is broadly consistent with the predictions from the subseasonal weather outlooks for July 2023 (26 June – 9 July 2023, 10 – 23 July 2023, and 24 July – 6 August).

Figure 2: Temperature anomalies for July 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 At the start of July, the Madden-Julian Oscillation (MJO) signal was present over the Indian Ocean (Phase 2). This signal decayed during the first week of July, with no significant MJO activity for the rest of the month. Typically for June, Phase 2 tends to bring drier conditions in northern Southeast Asia and bring wetter conditions to the western Maritime Continent (somewhat discernible in Figure 1).

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 El Niño conditions were likely present during July 2023. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) were consistent with El Niño conditions, with some signs of El Niño-like response in some of the key atmospheric indicators (cloudiness). El Niño events tend to bring drier-than-average conditions to much of the Maritime Continent during the June to August period.

August 15, 2023

Review of Regional Haze Situation for July 2023

1.1 Southwest Monsoon conditions persisted in July 2023, with the monsoon rainband located predominantly over the northern ASEAN region. The prevailing winds over areas north of the equator blew mainly from the southeast or southwest, while the prevailing winds over areas south of the equator blew mostly from the east or southeast (Figure 1). Typhoon Talim (Figure 9) and Super Typhoon Doksuri (Figure 10) brought about periods of strong winds over the northern half of the equator.

1.2 Over the southern ASEAN region, brief periods of dry weather conditions were observed for most of July 2023. Towards the end of the month, dry conditions persisted over Kalimantan with clusters of scattered hotspots and slight to moderate smoke haze observed over the western and southeastern parts of Kalimantan. On some days, smoke haze emanating from clusters of hotspots in West Kalimantan was observed to drift northwards into western Sarawak. On 28 July 2023, Alert Level 2 was activated for Kalimantan as hotspot counts were persistently high and there was an increasing risk of transboundary haze. Over the northern ASEAN region, wet weather was observed on most days during the month, subduing the overall haze situation in the region. High rainfall amounts were recorded over the northern parts of the Philippines due to Typhoon Talim which made landfall over the Philippines on July 13, 2023 and Super Typhoon Doksuri which passed the northern tip of the Philippines between July 25 and July 27, 2023.

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

1.3 Over the southern ASEAN region, there was a rise in overall hotspot activity due to periods of drier conditions, with the hotspot counts in the region higher or comparable to previous years (Figure 2). Notably, Kalimantan experienced the most significant rise in hotspot activity, with the highest count recorded in five years. Over the Mekong sub-region, the overall hotspot count in 2023 was mostly comparable to or lower than in previous years (Figure 3).

Figure 2: Hotspot counts for the southern ASEAN region for July (2019-2023) based on NOAA-20 satellite surveillance.

Figure 3: Hotspot counts for the northern ASEAN region for July (2019-2023) based on NOAA-20 satellite surveillance.

1.4 Towards the end of July 2023, hotspot activities were persistent in West and South Kalimantan, as well as parts of the Lesser Sunda Islands (Figure 4). The overall fire intensity for the ASEAN region was low, except for over parts of western Kalimantan where moderate fire intensity was detected (Figure 5). Slight to moderate smoke haze was observed over the western and southeastern parts of Kalimantan (Figures 6, 7 and 8).

Figure 4: Distribution of hotspots detected in July 2023 based on NOAA-20 satellite surveillance.

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

Figure Figure 6: Number of days with moderate to dense haze observed in July 2023 based on NOAA-20 satellite surveillance.

Figure 7: Slight to moderate smoke haze was observed in West Kalimantan drifting northwards towards Sarawak on 27 July 2023. (Source: Himawari-9 satellite surveillance)

Figure 8: Moderate smoke plumes were observed to emit from the hotspots detected in South Kalimantan on 29 July 2023. (Source: NOAA-20 satellite surveillance)

Figure 9: Typhoon Talim over the western Pacific Ocean (Source: MODIS satellite surveillance)

Figure 10: Super Typhoon Doksuri over the western Pacific Ocean (Source: NOAA-20 satellite surveillance)

August 4, 2023

Subseasonal Weather Outlook (7 – 20 August 2023)

Issued: 4 August 2023
First forecast week: 7 August – 13 August 2023
Second forecast week: 14 August – 20 August 2023

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over much of the southern ASEAN region in the next fortnight (7 – 20 August). Drier conditions are also predicted over much of Mainland Southeast Asia and northern parts of the Philippines in Week 1 (7 – 13 August).

Wetter conditions are predicted over the central and southern Philippines as well as the surrounding region in the next fortnight (7 – 20 August).

Warmer than usual temperature is predicted over the eastern equatorial region in Week 1 (7 – 13 August). These warmer temperatures are predicted to extend westwards to cover most of the central and eastern equatorial region in Week 2 (14 – 20 August). Warmer than usual temperature is also predicted over much of the northern ASEAN region in the next fortnight (7 – 20 August).

No Madden-Julian Oscillation (MJO) signal was present at the start of August. Most models predict no significant MJO signal during the forecast period.