Monthly Archives: July 2025

July 31, 2025

Subseasonal Weather Outlook (4 – 17 August 2025)

Issued: 31 July 2025
First forecast week: 4 – 10 August 2025
Second forecast week: 11 – 17 August 2025

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over central and eastern Mainland Southeast Asia in Week 1 (4 – 10 August). Wetter conditions are predicted over much of the mentioned area in Week 2 (11 – 17 August), with the highest likelihood over southern Mainland Southeast Asia.

Wetter conditions are predicted over much of the Maritime Continent during the next fortnight (4 – 17 August).

Warmer than usual temperatures are predicted over much of Mainland Southeast Asia in Week 1 (4 – 10 August), in line with the predicted drier conditions.

A Madden-Julian Oscillation (MJO) signal was present over the Western Pacific (Phase 7) during the last week of July. Most models predict this signal to weaken by the start of August. Most models predict an MJO signal to emerge in Phase 1 (Western Hemisphere) during Week 1, with some models predicting the signal to continue propagating eastwards to the Indian Ocean (Phase 2) during Week 2.

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.

July 30, 2025

Review of Regional Weather for June 2025

1. Overview

1.1 During June 2025, Southeast Asia experienced a mixed of below- to above-average rainfall, with parts of the western Maritime Continent experiencing below- to near-average rainfall and above-average rainfall over the southeastern Maritime Continent (Figure 1). The largest positive (wetter) anomalies were recorded over central Viet Nam. However, there were notable disagreements between GSMaP-NRT and CPC Unified Gauge datasets. CPC Unified Gauge recorded more regions with below-average rainfall, in particular over parts of southeastern Mainland Southeast Asia and the central Maritime Continent, where GSMaP-NRT recorded near- to above-average rainfall.

1.2 The observed rainfall anomaly pattern of below-average rainfall over parts of western Mainland Southeast Asia is mostly consistent with the predictions from the subseasonal weather outlooks for June 2025 (26 May – 8 June 2025, 9 – 22 June 2025, and 23 June – 6 July 2025). The subseasonal weather outlooks for the other regions were mixed throughout the June 2025 period and is also reflective in the mixed of below- to above-average rainfall recorded. The observations are also somewhat consistent with the seasonal outlook for June 2025, where below-normal rainfall was predicted for parts of the western Maritime Continent and above-normal rainfall for parts of the southern Maritime Continent.

Figure 1: Rainfall anomalies for June 2025 based on GSMaP-NRT data (left) and CPC Global Unified Gauge-based Analysis data (right). The climatological reference period is 2001-2024. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Below-average and near-average temperatures were recorded over much of Mainland Southeast Asia in June 2025, while near-average and above-average temperatures were recorded over most of the Maritime Continent, except over the Philippines and Papua where below-average temperature were recorded (Figure 2). The coldest anomalies (-0.5°C – -1°C below average) were recorded over parts of Cambodia and Viet Nam while the warmest anomalies (1°C – 2°C above average) were recorded over central Sumatra.

Figure 2: Temperature anomalies for June 2025 based on ERA-5 reanalysis. The climatological reference period is 2001-2024. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 There was no discernible Madden-Julian Oscillation (MJO) signal for most of June based on the RMM diagram (Figure 3). At the start of the month, the MJO was inactive based on the RMM Index. An MJO signal developed over the Western Pacific in the end of Week 1, propagated eastwards through the Western Pacific (Phases 6 and 7) by the middle of Week 2. The MJO signal decayed over the Western Hemisphere (Phase 8) in Week 3 and remained inactive for the rest of the month. At this time of the year, Phases 7 and 8 tend to bring drier conditions to parts of the Maritime Continent while Phase 4 tends to bring wetter conditions to this region. However, with the MJO being only briefly active during May, the MJO had little effect on the overall recorded rainfall during the month.

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 ENSO-neutral conditions were present in June 2025.

July 19, 2025

Alert20250719 – Activation of Alert Level 2 for the Southern ASEAN Region

Activation of Alert Level 2 for the Southern ASEAN Region

Prevailing dry weather conditions over the southern ASEAN region in recent days have led to an escalation in hotspot and smoke haze activities. Based on satellite surveillance, moderate smoke haze was observed to emanate from clusters of hotspots detected in the central parts of Sumatra. Some transboundary haze was observed to drift into western Peninsular Malaysia. 79 and 65 hotspots were detected in Sumatra on 18 and 19 July 2025 respectively from the NOAA-20 satellite. Few hotspots were also detected elsewhere in the southern ASEAN region.

Dry weather is expected to persist over the southern ASEAN region in the coming days, with prevailing winds likely to blow from the southeast or southwest. Under these conditions, the hotspot and smoke haze situation could worsen with an increased risk of transboundary smoke haze occurrence.

July 16, 2025

Subseasonal Weather Outlook (21 July – 3 August 2025)

Issued: 16 July 2025
First forecast week: 21 – 27 July 2025
Second forecast week: 28 July – 3 August 2025

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over much of the Maritime Continent and parts of southeastern Mainland Southeast Asia in the next fortnight (21 July – 3 August).

Wetter conditions are predicted over much of the rest of Mainland Southeast Asia and the very northeastern part of the Maritime Continent in Week 1 (21 – 27 July).

Warmer than usual temperatures are predicted over most of the Maritime Continent and parts of southeastern Mainland Southeast Asia in the next fortnight (21 July – 3 August), in line with the predicted drier conditions.

A Madden-Julian Oscillation (MJO) signal emerged over the Maritime Continent (Phase 4) during the second week of July. Most models predict this signal to propagate eastwards reaching the Western Pacific (Phases 6 and 7) by the end of Week 1. In Week 2, most models predict the MJO signal to weaken.

July 3, 2025

Review of Regional Haze Situation for June 2025

1.1 Southwest Monsoon conditions became fully established over the ASEAN region in June 2025. Over much of the southern ASEAN region, the prevailing winds blew mainly from the southeast. The prevailing winds over the Mekong sub-region were mostly southwesterly or westerly while the regions close to the Equator and the Philippines experienced winds that were mostly light and variable in direction (Figure 1).

1.2 Rainy weather prevailed over most parts of the ASEAN region during the review period. In particular, moderate to heavy showers fell on several days over the central parts of Viet Nam under the influence of Typhoon WUTIP. The resulting flooding and landslides were reported across multiple areas in the central parts of Viet Nam . In contrast, drier conditions were observed over Sumatra, Java and the Lesser Sunda Islands (Figure 1). In view of the expected continuation of the dry weather, Alert Level 1 for the southern ASEAN region was activated on 12 June 2025.

Figure 1: Average Daily Rainfall and Mean Winds for June 2025. (Source: JAXA GsMaP and GFS, respectively)

1.3 Hotspot activity in the northern ASEAN region was mostly subdued in June 2025 due to the prevailing wet weather conditions. The total number of hotspots were lower or comparable to the same period of previous years (Figure 2). Meanwhile, hotspot counts in the southern ASEAN region were generally comparable to previous years except for Sumatra which recorded the highest number of hotspots in five years (Figure 3).

Figure 2: Hotspot counts for the northern ASEAN region for June (2021-2025) based on NOAA-20 satellite surveillance.

Figure 3: Hotspot counts for the southern ASEAN region for June (2021-2025) based on NOAA-20 satellite surveillance.

1.4 In June 2025, a few to isolated hotspots were detected in the ASEAN region, particularly in the northern and central parts of Sumatra, as well as parts of Viet Nam where the fires were more persistent and intense. Slight localised smoke plumes were observed emanating from hotspots in West Kalimantan, Sarawak and the northern and central parts of Sumatra on some days (Figure 4, 5 and Figure 6).

Figure 4: Distribution of hotspots detected in June 2025 based on NOAA-20 satellite surveillance.

Figure 5: Maximum fire intensity in June 2025 based on NOAA-20 satellite surveillance.

Figure 6: Localised smoke plume was observed to emit from hotspots detected in northern Sumatra on 22 June 2025. (Source: NOAA-20 and Himawari-9 satellite surveillance).

July 2, 2025

Subseasonal Weather Outlook (7 – 20 July 2025)

Issued: 2 July 2025
First forecast week: 7 July – 13 July 2025
Second forecast week: 14 July – 20 July 2025

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Drier conditions are predicted over southern Mainland Southeast Asia and parts of the northeastern Maritime Continent in the next fortnight (7 – 20 July).

Wetter conditions are predicted over much of northern Mainland Southeast Asia in Week 1 (7 – 13 July).

Warmer than usual temperatures are predicted over most of the Maritime Continent and southern Mainland Southeast Asia in the next fortnight (7 – 20 July).

There was no discernible Madden-Julian Oscillation (MJO) signal at the beginning of July. Most models predict no significant MJO activity during the forecast period.