Monthly Archives: August 2024

August 28, 2024

Subseasonal Weather Outlook (2 – 15 September 2024)

Issued: 28 August 2024
First forecast week: 2 – 8 September 2024
Second forecast week: 9 – 15 September 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted for much of the northern ASEAN region in the next fortnight (2 – 15 September). In Week 1 (2 – 8 September), the highest likelihood of wetter conditions is over southern Mainland Southeast Asia.

Drier conditions are predicted over the central equatorial region in Week 1 (2 – 8 September).

Warmer than usual temperature is predicted over most of the Maritime Continent in the next fortnight (2 – 15 September). Warmer than usual temperature is also predicted over northern Mainland Southeast Asia in Week 1 (2 – 8 September).

A Madden-Julian Oscillation (MJO) signal was present over the Indian Ocean (Phase 3) towards the end of August based on the RMM index. For Week 1, most models predict an MJO signal to propagate from the Maritime Continent (Phases 4 and 5) to the Western Pacific (Phases 6 and 7). For Week 2, there is disagreement between the models whether this signal will continue propagating eastwards or weaken and become indiscernible.

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.

August 22, 2024

Summary of the 4th Workshop on Subseasonal to Seasonal Prediction for Southeast Asia (S2S-SEA IV)

August 2023, Singapore

The S2S-SEA IV workshop in August 2023, led by the ASMC and the Centre for Climate Research Singapore, marked the end of a four-part workshop series on Subseasonal-to-Seasonal (S2S) prediction in Southeast Asia. The workshop series aimed to build capacity and enhance collaboration among the National Meteorological and Hydrological Services (NMHSs) in the ASEAN region regarding S2S prediction. The fourth S2S-SEA Workshop included two virtual sessions (15 and 30 August) and an in-person segment between 22 and 24 August 2023, conducted in Singapore. Fifteen NMHS representatives from nine ASEAN Member States attended the in-person training, along with six trainers. Encompassing the in-person training, the two virtual sessions allowed more users to participate in the workshop, as well as more time for reflection in between the sessions. An additional 26 users and three trainers attended the virtual sessions, leading to a total number of 50 participants in SEA-SEA IV over the in-person and virtual sessions.

Key takeaways shared by the participants during the workshop included information on latest updates on sources of S2S predictability (including questions that are still unanswered), a better awareness of S2S products, and the procedure to give a S2S briefing to users (something NMHSs are not always trained in). The workshop also discussed the future of S2S predictions and plans for collaboration in the ASEAN region. Common challenges faced by NMHSs raised in the workshop include the need for improved communication, data access, and automation. Plans were made for fortnightly discussions between ASEAN NMHSs to review climate drivers and S2S outlooks.

Since the first workshop in 2017, many of the NMHSs in Southeast Asia have moved from research to delivering operational S2S products. While there is still more to do around delivering actionable products, discussions during the S2S-SEA IV highlighted that sharing experiences and expertise in the region is useful for the continued development of S2S predictions in Southeast Asia.

Participants during Virtual Sessions of the S2S SEA-IV workshop.

Group photo during the S2S-SEA Workshop, Singapore (in-person, 22-24 August 2023).

Workshop report

S2S SEA SIV report

August 19, 2024

Review of Regional Weather for July 2024

1. Overview

1.1 During July 2024, below-average rainfall was recorded over parts of the southern ASEAN region, in particular over the equatorial region, while above-average rainfall was recorded over parts of the central equatorial region and near-average rainfall over the southernmost region (Figure 1). For the northern ASEAN region, above-average rainfall was recorded over eastern and southern Mainland Southeast Asia as well as over the Philippines, while a mix of below- to above-average rainfall was recorded over northern Mainland Southeast Asia. The largest positive (wetter) anomalies were recorded over southern coast of Myanmar based on GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates. In contrast, the largest negative (drier) anomalies were recorded over northern Sumatra (in both GSMaP-NRT and CMORPH-Blended).

1.2 The observed rainfall anomaly pattern of above-average rainfall over parts of the southern Mainland Southeast Asia coupled with below-average rainfall over parts of the equatorial region are broadly consistent with the predictions from the subseasonal weather outlooks for July 2024 (24 June – 7 July 2024 , 8 – 21 July 2024 and 22 July – 4 August 2024).

Figure 1: Rainfall anomalies for July 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 most of the Maritime Continent and northern Mainland Southeast Asia (Figure 2) in July 2024. The exceptions were over central and southeastern Mainland Southeast Asia, where below-to near-average temperature was recorded over parts of eastern Thailand, Cambodia and Vietnam. The warmest anomalies (more than 1°C above average) were recorded over Sumatra.

Figure 2: Temperature anomalies for July 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 The Madden-Julian Oscillation (MJO) was present over the Indian Ocean (Phase 3) for the first week of July based on the RMM index (Figure 3). The MJO signal weakened and became indiscernible for much of the rest of July, except during mid-July when an MJO signal emerged briefly for a few days over the Maritime Continent (Phases 4 and 5). Typically for July, Phases 3 and 4 tend to bring wetter conditions to the Maritime Continent and southern Mainland Southeast Asia, and Phase5 tends to bring wetter conditions to the eastern 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 July, although the lingering effect from the El Niño still likely contributed to the warmer temperatures observed in Figure 2.

August 15, 2024

Subseasonal Weather Outlook (19 August – 1 September 2024)

Issued: 14 August 2024
First forecast week: 19 – 25 August 2024
Second forecast week: 26 August – 1 September 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

For the equatorial region, wetter conditions are predicted over much of the region in Week 1 (19 – 25 August). In Week 2 (26 August – 1 September), wetter conditions are predicted to continue over the eastern half of the equatorial region, with drier conditions predicted to develop over much of the western half.

Elsewhere, wetter conditions are predicted over much of central and southern Mainland Southeast Asia and the Philippines in Week 2 (26 August – 1 September), while drier conditions are predicted to persist over the southern Maritime Continent in the next fortnight (19 August – 1 September).

Warmer than usual temperature is predicted over much of central and southern Mainland Southeast Asia and the Philippines in Week 1 (19 – 25 August). In Week 2 (26 August – 1 September), warmer temperatures are predicted over the western, southern, and eastern Maritime Continent.

A Madden-Julian Oscillation (MJO) signal was present over the Western Hemisphere and Africa (Phase 1) towards the middle of August based on the RMM index. Most models predict the signal to continue propagating eastwards, reaching the Maritime Continent (Phases 4 and 5) by the end of Week 1 and into Week 2, in line with the wetter conditions predicted.

August 6, 2024

Review of Regional Haze Situation for July 2024

1.1 In July 2024, the Southwest Monsoon conditions continued over the ASEAN region. Over the northern ASEAN region, the prevailing winds blew mostly from the southwest to west. In the southern ASEAN region, the prevailing winds over areas near the Equatorial region were observed to be generally weak and variable in direction while southeasterly winds were observed over the rest of the region (Figure 1).

1.2 Showers were observed over most of the ASEAN region during the review period, apart from Java and the Lesser Sunda Islands where dry conditions were observed (Figure 1). Parts of Peninsular Malaysia, Sumatra, and Kalimantan also experienced drier conditions during the latter half of the review period. On 17 July 2024, the Alert Level 1 for the southern ASEAN region was activated, signalling the start of the traditional dry season for the region. Over the northern ASEAN region, heavy rainfall was recorded over the northern parts of the Philippines due to the influence of Tropical Storm Prapiroon and Typhoon Gaemi situated over the northern parts of the South China Sea and the northwest Pacific Ocean respectively during the latter half of July (Figure 9 and 10). Rainfall was also observed to be high over the western coastal areas of Myanmar (Figure 1).

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

1.3 Over the southern ASEAN region, the hotspot counts were generally lower or comparable to previous years, except for the hotspot counts in Sumatra which was the highest compared to the past 5 years (Figure 2). Nonetheless, the hotspot activity for the southern ASEAN region remained relatively low compared to other parts of the year. Over the northern ASEAN region, the hotspot counts were lower or comparable to the past few years (Figure 3).

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

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

1.4 Hotspot activities were intense and persistent especially in the western parts of Kalimantan and parts of Sumatra towards the end of July 2024 (Figure 4). Slight to moderate localised smoke plumes were observed to emanate from hotspots detected in the western and central parts of Kalimantan and parts of Sumatra (Figure 5, 6, 7 and 8).

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

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

Figure 6: Number of days with moderate to dense smoke haze observed in July 2024 based on satellite imagery, ground observations, and air quality reports.

Figure 7: Slight localised smoke plumes were observed to emanate from a few hotspots in the western parts of Kalimantan on 26 July 2024. (Source: Himawari-9 satellite surveillance)

Figure 8: Slight localised smoke plumes were observed to emanate from a few hotspots over the central parts of Sumatra on 28 July 2024. (Source: Himawari-9 satellite surveillance)

Figure 9: Tropical Storm Prapiroon over the northern parts of the South China Sea (Source: NOAA-20 satellite surveillance)

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

August 1, 2024

Subseasonal Weather Outlook (5 – 18 August 2024)

Issued: 31 July 2024
First forecast week: 5 – 11 August 2024
Second forecast week: 12 – 18 August 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over southern and eastern Mainland Southeast Asia and the Philippines in the next fortnight (5 – 18 August). Drier conditions are also predicted over the southern Maritime Continent in the next fortnight.

Wetter conditions are predicted over much of the equatorial region in the next fortnight (5 – 18 August).

Warmer than usual temperature is predicted over much of southern and eastern Mainland Southeast Asia, and the Philippines in the next fortnight (5 – 18 August). Warmer than usual temperature is also predicted over parts of the western and southern Maritime Continent in the next fortnight.

No Madden-Julian Oscillation (MJO) signal was present during end of July based on the RMM index. Most models predict no significant MJO activity during the forecast period.