Monthly Archives: June 2024

June 20, 2024

Subseasonal Weather Outlook (24 June – 7 July 2024)

Issued: 19 June 2024
First forecast week: 24 – 30 June 2024
Second forecast week: 1 – 7 July 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over much of Mainland Southeast Asia and the Philippines in Week 1 (24 – 30 June). These wetter conditions are predicted to persist in Week 2 (1 – 7 July), although with less confidence over the Philippines.

Warmer than usual temperature is predicted over the southern half of Southeast Asia in the next fortnight (24 June – 7 July).

No Madden-Julian Oscillation (MJO) signal was present in mid-June based on the RMM index. 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.

June 14, 2024

Review of Regional Haze Situation for May 2024

1.1 In early May 2024, the prevailing winds, especially over the Mekong sub-region and the South China Sea, were light and variable as inter-monsoon conditions continued. Prevailing winds for areas located south of the Equator then transitioned into southeasterlies from mid-May onwards, indicating the development of the Southwest Monsoon. Winds located to the east of the Philippines continue to be easterly in May 2024. (Figure 1).

1.2 Rainfall was observed over most of the ASEAN region except for Java and the Lesser Sunda Islands, where conditions were drier. The increase in precipitation in the Mekong sub-region compared to April 2024 resulted in the reduction of hotspots in the sub-region. (Figure 1) The Alert level was downgraded to Level 2 on 6 May, Level 1 on 13 May and subsequently Level 0 on 23 May, signaling the end of the dry season for the Mekong sub-region.

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

1.3 The hotspot count in May 2024 for Peninsular Malaysia, Sabah and Sarawak were higher when compared to previous years. However, for Kalimantan and Sumatra, the hotspot counts for May 2024 were lower. (Figure 3). Elsewhere in the ASEAN region, especially in the Mekong sub-region, the number of hotspots remain comparable with previous years.

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

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

1.4 In May 2024, isolated to scattered hotspots were detected mainly in the Mekong sub-region and the Philippines, especially in the northern parts of Lao PDR and the southern parts of Myanmar where fire intensity and hotspot persistency were more pronounced. (Figure 4 and 5) During early May, moderate to dense transboundary smoke haze was observed over the northern parts of Lao PDR, the northern parts of Thailand, as well as the eastern and southern parts of Myanmar. The transboundary smoke haze was shown to drift in the north-east direction into the northern parts of Viet Nam and Lao PDR (Figure 6 and 7).

1.5 Hotspot activity remained mostly subdued in the southern ASEAN region except for a few persistent hotspots in the eastern parts of Peninsular Malaysia (Figure 4). Localised smoke plumes were observed to emanate from these hotspots on some days. (Figure 8)

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

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

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

Figure 7: Widespread moderate transboundary smoke haze covering the northern parts of Lao PDR and Thailand on 1 May 2024. (Source: NOAA-20 satellite surveillance)

Figure 8: On 15 May 2024, localised smoke plumes were observed to emanate from hotspots in the eastern parts of Peninsular Malaysia and the southern parts of Thailand. (Source: NOAA-20 satellite surveillance)

June 13, 2024

Review of Regional Weather for May 2024

1. Overview

1.1 During May 2024, much of the equatorial region experienced above-average rainfall, while much of the southern parts of the Maritime Continent and the Philippines experienced below-average rainfall (Figure 1). A mix of near- and above-average rainfall was recorded over much of Mainland Southeast Asia, although there was disagreement over Cambodia with GSMaP-NRT (Figure 1, left) recording near- to above-average rainfall, while CMORPH-Blended (Figure 1, right) recorded below-to near-average rainfall. The largest negative (drier) anomalies were recorded over southern Philippines, Java, and parts of northeastern Borneo in GSMap-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right). The larger positive (wetter) anomalies were recorded over Sumatra and central Borneo (in both GSMap-NRT and CMORPH-Blended).
1.2 The observed rainfall anomaly pattern of a mix of below- and above-average rainfall over the northern ASEAN region and above-average rainfall over the equatorial region is consistent with the predictions from the subseasonal weather outlooks for May 2024 (29 April – 12 May 2024 , 13 – 26 May 2024 and 27 May – 9 June 2024).

Figure 1: Rainfall anomalies for May 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 ASEAN region in May 2024 (Figure 2). The warmest anomalies (more than 2°C above average) were recorded over southern Thailand and northeastern Borneo. Based on ERA-5 reanalysis, Temperatures in May 2024 were among the 10% warmest values for May over southern Sumatra, southern Thailand and Myanmar, parts of Borneo and most of the Philippines.

Figure 2: Temperature anomalies for May 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 active for much the second half of May 2024, based on the RMM index (Figure 3). In the first week of May, an MJO signal propagated eastwards through the Maritime Continent (Phases 4 and 5) before becoming inactive. In the second half of the May, the signal reached re-emerged over the Indian Ocean (Phases 2 and 3) and remained there until the end of the month. For May, Phases 2 to 5 tend to bring wetter conditions to parts of the Maritime Continent (the western Maritime Continent in Phase 2, much of the region for Phases 3 and 4, and the eastern Maritime Continent in Phase 5). Therefore, the MJO may have contributed to the wetter conditions in the equatorial region in May.

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 El Niño event has now ended, although the lingering effect of the El Niño still likely contributed to the warmer temperatures observed in Figure 2.

June 6, 2024

Subseasonal Weather Outlook (10 – 23 June 2024)

Issued: 6 June 2024
First forecast week: 10 – 16 June 2024
Second forecast week: 17 – 23 June 2024

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are predicted over western Mainland Southeast Asia in Week 1 (10 – 16 June). Drier conditions are predicted over parts of the western Maritime Continent and southern Mainland Southeast Asia in Week 1 (10 – 16 June).

Warmer than usual temperature is predicted over most of the Maritime Continent in the next fortnight (10 – 23 June). Warmer than usual temperature is also predicted over the southern half of Mainland Southeast Asia in Week 2 (17 – 23 June).

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

June 5, 2024

22nd ASEAN COF (May 2024)

Twenty Second Session of the ASEAN Climate Outlook Forum (ASEANCOF-22)

27-30 May 2024, DMH Lao PDR

Consensus Bulletin for June-July-August (JJA) 2024 Season

The ASEAN Climate Outlook Forum (ASEANCOF) is an avenue to collaboratively develop consensus-based seasonal climate outlooks and related information on a regional scale. The forum’s outlook and its activities contribute significantly to one of the key roles of the ASEAN Specialised Meteorological Centre (ASMC), which is to conduct climate and seasonal prediction for the Association of Southeast Asian Nations (ASEAN) region through pooling the expertise of ASEAN National Meteorological and Hydrological Services (NMHSs). In 2021, the ASEANCOF Working Group was established with the goal to guide and support the long-term development of ASEANCOF, in particular with regard to the implementation of objective outlooks.

The Twenty-Second session of ASEANCOF (ASEANCOF-22) was organised by the Department of Meteorology and Hydrology of Lao PDR, RIMES, the ASEANCOF Working Group, and WMO. Participants from the NMHSs of ASEAN Member States created a consensus forecast for the boreal summer monsoon 2024 in the ASEAN region. The consensus for the June-July-August (JJA) 2024 outlook was achieved through a hybrid session, which included presentations from different NMHSs, questionnaires, and discussions regarding the current climate conditions and predictions for Southeast Asia. There was also two-day pre-COF training, conducted by the UK Met Office under the WISER Asia Pacific project and RIMES. The theme of ASEANCOF-22 was Agriculture and Climate Services, with a focus on drought. On the last day of ASEANCOF-22, a sharing session was held which included presentations from UN ESCAP, FAO, and WFP, as well as discussion on ways to improve ASEANCOF.

Conditions and Outlook

Recent analysis of sea surface temperature (SST) anomalies over the equatorial Pacific shows average to slightly below-average SSTs across the equatorial Pacific Ocean, and along with atmospheric indicators such as trade wind strength and cloudiness, indicate ENSO-neutral conditions. In the Indian Ocean, the Indian Ocean Dipole is also neutral.

The international climate outlook predicts that a La Niña is likely to develop sometime during JJA 2024. After JJA 2024, most models predict La Niña conditions to continue until the end of the year.
There is a chance that a weak positive Indian Ocean Dipole (IOD) may become established during JJA 2024 based on the model predictions. However, it is predicted to most likely be short-lived.

The onset of the Southwest monsoon season has been or is expected to be near average for much of Mainland Southeast Asia, apart from Thailand where the onset is later than average. The onset of the Southwest monsoon for much of the Maritime Continent has been or is expected to be near average. The strength of the Southwest monsoon is predicted to be near average over most of the Southeast Asia, based on model predictions.

During JJA 2024, tropical cyclone frequency is predicted to be below average around the Philippine Sea and the Bay of Bengal, and near average around South China Sea.

Taking into consideration the national level forecasts, the present state of the climate, and the forecasts available from the GPCs, ASEANCOF-22 agreed on the following consensus-based outlook for JJA 2024 over the ASEAN region:

RAINFALL

Above-normal rainfall is predicted over northern Myanmar, parts of Cambodia and parts of the equatorial region, including Brunei Darussalam and middle part of East Malaysia. Near- to above-normal rainfall is predicted over southern Thailand, western part of East Malaysia, and the southern Philippines, as well as parts of Mainland Southeast Asia including western Myanmar, northwestern Lao PDR, parts of Cambodia, and southern Viet Nam.

Below-normal rainfall is predicted over the western part of Northern Philippines. Below- to near- normal rainfall is predicted over southern Lao PDR, the rest of Northern Philippines, and southernmost parts of Southeast Asia. Elsewhere, near-normal rainfall is predicted.¹.

TEMPERATURE

Above normal temperature is predicted over most of Southeast Asia, apart from over much of Myanmar, Lao PDR, Cambodia, Brunei Darussalam, and the Philippines where near- to above-normal temperature is predicted.

¹This is based on the climatology period 1991-2020. However, at the national level, Myanmar is using the 1981-2010 climatology as their base period.

Refer to Annex A for reference on what is meant by “above, near, or below normal” in the outlook. For more information on the boreal (Northern Hemisphere) summer monsoon outlook and further updates on the national scale, the relevant NMHSs should be consulted (see Annex B).

Consensus Maps for JJA 2024 Season

The following maps provide the probabilistic outlooks for JJA 2024 season in terms of tercile categories of “Above Normal” (AN: upper tercile), “Near Normal (NN: middle tercile) and “Below Normal” (BN: lower tercile).

PROBABILISTIC RAINFALL OUTLOOK

PROBABILISTIC TEMPERATURE OUTLOOK

Meeting Documents

ASEANCOF-22 Outlook Bulletin

Acknowledgements

ASEANCOF would like to convey its appreciation to the NMHSs of the ASEAN Member States for sharing their national level forecasts, the Global Producing Centres, the Southeast Asia Regional Climate Centre – Network, RIMES, UN ESCAP, FAO, WFP, and other partners of ASEANCOF for sharing their products and expertise, and the World Meteorological Organization Regional Office in Asia and the Southwest Pacific (WMO-RAP) for their continued support of ASEANCOF. The Forum would also like to thank DMH Lao PDR for hosting the forum, with support from RIMES, and CREWS Cambodia and Lao PDR and WISER Asia Pacific for the funding support provided for the meeting.