Monthly Archives: November 2024

November 21, 2024

Subseasonal Weather Outlook (25 November – 8 December 2024)

Issued: 20 November 2024
First forecast week: 25 November – 1 December 2024
Second forecast week: 2 December – 8 December 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over parts of the central equatorial region and the southern Maritime Continent in Week 1 (25 November – 1 December). Wetter conditions are predicted to persist over much of the southern Maritime Continent in Week 2 (2 – 8 December).

Warmer than usual temperature is predicted over most of the Maritime Continent, apart from the southern region, and southern parts of Mainland Southeast Asia in the next fortnight (25 November – 8 December).

A weak Madden-Julian Oscillation (MJO) signal was present over the Indian Ocean (Phase 2) during mid-November. Most models predict this MJO signal to strengthen and propagate across the Indian Ocean (Phases 2 and 3), and then during the forecast period, propagate through the Maritime Continent (Phases 4 and 5).

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.

November 15, 2024

Review of Regional Weather for October 2024

1. Overview

1.1 During October 2024, the ASEAN region experienced a mix of below- and above-average rainfall. For the Maritime Continent, much of the western region experienced below-average rainfall while much of the eastern region as well as northern and central Philippines experienced above-average rainfall (Figure 1). Above-average rainfall was recorded over much of southern Mainland Southeast Asia, with below-average rainfall over parts of northwestern and eastern Mainland Southeast Asia, although there was disagreement over central Viet Nam with GSMaP-NRT (Figure 1, left) recording below-average rainfall, while CMORPH-Blended (Figure 1, right) recorded above-average rainfall. The largest negative (drier) anomalies were recorded over southern Sumatra in both GSMap-NRT and CMORPH-Blended. The largest positive (wetter) anomalies were recorded over central Philippines (in both GSMap-NRT and CMORPH-Blended), partly associated with Tropical Storm Trami and Typhoon Kong-rey in October 2024.

1.2 The observed rainfall anomaly pattern of a mix of below- and above-average rainfall in the ASEAN region, with below-average rainfall over the western Maritime Continent is consistent with the predictions from the subseasonal weather outlooks for October 2024 (30 September – 13 October 2024 and 14 – 27 October 2024).

Figure 1: Rainfall anomalies for October 2024 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2023. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Above-average temperatures were recorded over the much of ASEAN region in October 2024 (Figure 2). The warmest anomalies (more than 1°C above average) were recorded mainly over southern Sumatra based on ERA-5 reanalysis.

Figure 2: Temperature anomalies for October 2024 based on ERA-5 reanalysis. The climatological reference period is 2001-2023. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 2.1 The Madden-Julian Oscillation (MJO) was active from the end of the second week of October 2024, based on the RMM index (Figure 3). An MJO signal was present over the Western Hemisphere (Phase 1) at the start of October, which quickly weakened and remained inactive for much of the first two weeks of October. At the end of the second week, the MJO signal emerged over the Maritime Continent (Phases 4 and 5), propagated eastwards through the Maritime Continent (Phases 4 and 5) in Week 3, and through the Western Pacific (Phases 6 and 7) during the last week of the month. For October, Phases 4 to 5 tend to bring wetter conditions to parts of southern Mainland Southeast Asia and the Philippines (in line with Figure 1), Phase 6 tends to bring wetter conditions over the Philippines, and Phase 7 tends to bring drier conditions to western 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 The tropical Pacific was in an ENSO neutral state during October.

November 8, 2024

Review of Regional Haze Situation for October 2024

1.1 In October 2024, the Southeast Monsoon transitioned to the inter-monsoon conditions. As the monsoon rainband shifted towards the Equator, the winds over the equatorial regions became light and variable in direction (Figure 1). However, strong winds affected the northern parts of the Philippines at times, driven by Tropical Storm Trami and Super Typhoon Kong-Rey (Figures 8 and 9).

1.2 Showers prevailed over most of the ASEAN region in October 2024, apart from Java, the Lesser Sunda Islands and the northern and central parts of the Mekong sub-region where conditions were relatively drier (Figure 1). On 14 October 2024, ASMC downgraded the Alert Level for the southern ASEAN region from Level 1 to Level 0, following increased shower activity, marking the end of the dry season of the region. Towards the end of the month, heavy rainfall affected the northern and central parts of the Philippines, influenced by Tropical Storm Trami and Typhoon Kong-Rey, which were located over the northern South China Sea and the northwestern Pacific Ocean, respectively (Figures 8 and 9).

Figure 1: Average Daily Rainfall and Mean Winds for October 2024. (Source: JAXA GsMaP and GFS, respectively)

1.3 Over the ASEAN region, hotspot counts in October 2024 were generally comparable or lower than the same month of previous years (Figure 2 and 3) except in Thailand where the highest hotspot counts over the past five years was recorded. Despite this, the overall hotspot activity in the northern ASEAN region remained relatively low compared to previous years.

Figure 2: Hotspot counts for the southern ASEAN region for October (2020-2024) based on NOAA-20 satellite surveillance.

Figure 3: Hotspot counts for the northern ASEAN region for October (2020-2024) based on NOAA-20 satellite surveillance.

1.4 During the second half of October 2024, persistent and intense hotspots were detected mostly in the central and southern parts of Sumatra, the central and southeastern parts of Kalimantan and parts of Sulawesi and the Lesser Sunda Islands (Figure 4 and 5). Slight localised smoke plumes were observed to emanate from hotspots detected in the southeastern parts of Kalimantan and the southern parts of Sumatra (Figure 6 and 7).

Figure 4: Distribution of hotspots detected in October 2024 based on NOAA-20 satellite surveillance.

Figure 5: Maximum fire intensity in October 2024 based on NOAA-20 satellite surveillance.

Figure 6: Slight localised smoke plumes were observed to emanate from a few hotspots in the southeastern parts of Kalimantan on 27 October 2024. (Source: NOAA-20 satellite surveillance)

Figure 7: Slight localised smoke plume was observed to emanate from a few hotspots over the southern parts of Sumatra on 29 October 2024. (Source: NOAA-20 satellite surveillance)

Figure 8: Tropical Storm Trami over the northern parts of the South China Sea (Source: AQUA satellite surveillance)

Figure 9: Typhoon Kong-Rey over the western Pacific Ocean (Source: NOAA-21 satellite surveillance)

November 6, 2024

Subseasonal Weather Outlook (11 – 24 November 2024)

Issued: 11 November 2024
First forecast week: 11 November – 17 November 2024
Second forecast week: 18 November – 24 November 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over the southern Maritime Continent in the next fortnight (11 – 24 November). Wetter conditions are also predicted over parts of southeastern Mainland Southeast Asia in Week 2 (18 – 24 November).

Warmer than usual temperature is predicted over the Maritime Continent, apart from the southern region, and southern coastal parts of Mainland Southeast Asia in the next fortnight (11 – 24 November).

A Madden-Julian Oscillation (MJO) signal was present over the Western Hemisphere and Africa (Phases 8 and 1) at the beginning of November. Most models predict this MJO signal to weaken by the start of Week 1, although a few predict it to propagate across the Indian Ocean (Phases 2 and 3), reaching the Maritime Continent (Phase 4) by the end of Week 2.