Subseasonal Weather Outlook and Review

1.1    The monsoon trough has migrated to the northern ASEAN region, with its position hovered mainly along the 10 N latitude line. The monsoon trough brought persistent shower activities over most parts of northern ASEAN.

1.2    Southwest Monsoon conditions, characterised by low level winds predominantly from the southeast or southwest, onset in the southern ASEAN region from the second half of June 2015. Wet weather conditions prevailed over the region in the first half of June 2015 and transited gradually to drier weather conditions with the onset of the traditional dry Southwest Monsoon season.

1.3    The rainfall over the southern ASEAN region in June has been lower than usual, which can partly be attributed to the prevailing moderate El Niño conditions in the equatorial Pacific Ocean which are likely to further develop in the months ahead. Sumatra, Java and southern Kalimantan received less than 50-75% of the normal rainfall; this is a typical precipitation pattern observed in southern ASEAN during a moderate to strong El Niño event. For the northern ASEAN region, below-normal rainfall has also been recorded in most parts except for central Thailand. The regional rainfall distribution for June 2015 is shown in Fig. 1A.

2.1    In the northern ASEAN region, hotspot activities continued to be subdued by the prevailing wet weather conditions.

2.2    In the southern ASEAN region, increased hotspot activities were detected during the period of drier weather in the second half of June. Persistent hotspots were observed on several days mostly in the provinces of Riau and Jambi in Sumatra. Smoke plumes and moderate haze were seen emanating from these hotspots.

2.3    In June 2015, most parts of Kalimantan were affected by showers. In the second half of June 2015, a period of drier weather led to the occurrence of isolated hotspots with localized smoke plumes in parts of western Kalimantan. Satellite images depicting some of the hotspot activities over the ASEAN region in June 2015 are shown in Figs. 2A to 2E.

1.1    The monsoon trough has migrated to the northern ASEAN region, with its position hovered mainly along the 10 N latitude line. The monsoon trough brought persistent shower activities over most parts of northern ASEAN.

1.2    Southwest Monsoon conditions, characterised by low level winds predominantly from the southeast or southwest, onset in the southern ASEAN region from the second half of June 2015. Wet weather conditions prevailed over the region in the first half of June 2015 and transited gradually to drier weather conditions with the onset of the traditional dry Southwest Monsoon season.

1.3    The rainfall over the southern ASEAN region in June has been lower than usual, which can partly be attributed to the prevailing moderate El Niño conditions in the equatorial Pacific Ocean which are likely to further develop in the months ahead. Sumatra, Java and southern Kalimantan received less than 50-75% of the normal rainfall; this is a typical precipitation pattern observed in southern ASEAN during a moderate to strong El Niño event. For the northern ASEAN region, below-normal rainfall has also been recorded in most parts except for central Thailand. The regional rainfall distribution for June 2015 is shown in Fig. 1A.

2.1    In the northern ASEAN region, hotspot activities continued to be subdued by the prevailing wet weather conditions.

2.2    In the southern ASEAN region, increased hotspot activities were detected during the period of drier weather in the second half of June. Persistent hotspots were observed on several days mostly in the provinces of Riau and Jambi in Sumatra. Smoke plumes and moderate haze were seen emanating from these hotspots.

2.3    In June 2015, most parts of Kalimantan were affected by showers. In the second half of June 2015, a period of drier weather led to the occurrence of isolated hotspots with localized smoke plumes in parts of western Kalimantan. Satellite images depicting some of the hotspot activities over the ASEAN region in June 2015 are shown in Figs. 2A to 2E.