Subseasonal Weather Outlook and Review

1.1    The Southwest Monsoon conditions in the region continued to persist in August 2015. In the northern ASEAN region, shower activities prevailed on most days in August 2015. In the southern ASEAN region, the first half of August 2015 experienced wetter than usual weather conditions, in particular around Sumatra, Peninsular Malaysia and Singapore, due to the indirect effects of Super Typhoon Souledor in the northern South China Sea. In the second half of August 2015, dry weather conditions persisted through the period.

1.2    Typhoon Goni, which formed over the western Pacific Ocean near Guam on 14 August, was steered westward towards the Philippines and eventually affected the northern islands of Cagayan province in Luzon Island on 21 August 2015. Typhoon Goni brought strong winds and heavy rains to northern Philippines destroying many homes and displacing many lives along its path. The typhoon clipped through the Philippines and continued on its track northwards before making landfall in the eastern parts of Taiwan on 23 August 2015.

1.3    The prevailing El-Nino conditions continue to bring drier than usual weather conditions over the southern ASEAN region, except in central Sumatra and Peninsular Malaysia where wetter than usual weather conditions were experienced. In the northern ASEAN region, near-average to below-average rainfall was received in the Mekong sub-region. The regional rainfall distribution for August 2015 is shown in Fig. 1A.

2.1    During the review period, hotspot activities in the northern ASEAN region continued to be subdued by shower activities. In contrast, in the southern ASEAN region, following the wet conditions in the first half of the month, a period of extended drier weather contributed to an escalation of hotspot activities for the rest of August 2015. Persistent land and forest fires were observed in central and southern Sumatra, in particular in Jambi and South Sumatra, which lead to widespread moderate to dense smoke haze over many parts of Sumatra.

2.2    Ground observations in Pekan Baru, Jambi and Rengat reported visibility of less than 1 km on several days. In addition, some moderate smoke haze from central Sumatra was observed to spread across the Strait of Malacca to affect Peninsular Malaysia. Several cities along the west coast of Peninsular Malaysia such as Penang and Kuala Lumpur reported low visibilities due to haze and the Air Pollution Index (API) readings were in the high-end of Moderate range.

2.3    In Kalimantan, it was dry with few occurrences of shower activities throughout August 2015. The increased hotspot activities in Kalimantan led to an accumulation of moderate to dense smoke haze especially over western and central Kalimantan. Prevailing southeasterly winds carried the smoke haze towards the northwest to affect Sarawak. On 24 August 2015, there was a deterioration in the air quality in several cities of Sarawak such as Sri Aman and Kuching with the API readings in these cities registering unhealthy levels. In the next few days, the occurrence of showers in Sarawak brought an improvement to the hazy conditions there. Satellite images depicting some of the hotspot activities over the ASEAN region in August 2015 are shown in Figs. 2A to 2E.

3.1    The sea surface temperatures (SSTs) in the tropical Pacific Ocean (SST) have continued to warm in August 2015. A strong El Niño currently prevails in the tropical Pacific Ocean.

3.2    The rainfall in the Southeast Asia region is showing a clear response to the El Niño development, with observed large-scale drier-than-normal conditions, in particular in the southern and eastern parts of the region. A consensus forecast based on international climate models and expert opinion suggests a high likelihood of the warming of the SST to continue. Further strengthening of El Niño conditions are likely in the coming months, and the El Nino is expected to prevail into early 2016.

3.3    Typically the impact of El Niño for the Southeast Asia region is drier than average rainfall conditions, especially for the southern parts of the ASEAN region during June to October. More locally-specific impact differs from place to place and for different seasons.

3.4    The ASEAN region is currently in the Southwest Monsoon season (June-September/early October), where the El Niño is known to have considerable impact (dryness) on the western part of the Maritime Continent. Thus with the current El Niño conditions, there is a high risk that the Sep-Oct-Nov season could experience extended periods of drier and warmer weather conditions in this part of Southeast Asia.

1.1    The Southwest Monsoon conditions in the region continued to persist in August 2015. In the northern ASEAN region, shower activities prevailed on most days in August 2015. In the southern ASEAN region, the first half of August 2015 experienced wetter than usual weather conditions, in particular around Sumatra, Peninsular Malaysia and Singapore, due to the indirect effects of Super Typhoon Souledor in the northern South China Sea. In the second half of August 2015, dry weather conditions persisted through the period.

1.2    Typhoon Goni, which formed over the western Pacific Ocean near Guam on 14 August, was steered westward towards the Philippines and eventually affected the northern islands of Cagayan province in Luzon Island on 21 August 2015. Typhoon Goni brought strong winds and heavy rains to northern Philippines destroying many homes and displacing many lives along its path. The typhoon clipped through the Philippines and continued on its track northwards before making landfall in the eastern parts of Taiwan on 23 August 2015.

1.3    The prevailing El-Nino conditions continue to bring drier than usual weather conditions over the southern ASEAN region, except in central Sumatra and Peninsular Malaysia where wetter than usual weather conditions were experienced. In the northern ASEAN region, near-average to below-average rainfall was received in the Mekong sub-region. The regional rainfall distribution for August 2015 is shown in Fig. 1A.

2.1    During the review period, hotspot activities in the northern ASEAN region continued to be subdued by shower activities. In contrast, in the southern ASEAN region, following the wet conditions in the first half of the month, a period of extended drier weather contributed to an escalation of hotspot activities for the rest of August 2015. Persistent land and forest fires were observed in central and southern Sumatra, in particular in Jambi and South Sumatra, which lead to widespread moderate to dense smoke haze over many parts of Sumatra.

2.2    Ground observations in Pekan Baru, Jambi and Rengat reported visibility of less than 1 km on several days. In addition, some moderate smoke haze from central Sumatra was observed to spread across the Strait of Malacca to affect Peninsular Malaysia. Several cities along the west coast of Peninsular Malaysia such as Penang and Kuala Lumpur reported low visibilities due to haze and the Air Pollution Index (API) readings were in the high-end of Moderate range.

2.3    In Kalimantan, it was dry with few occurrences of shower activities throughout August 2015. The increased hotspot activities in Kalimantan led to an accumulation of moderate to dense smoke haze especially over western and central Kalimantan. Prevailing southeasterly winds carried the smoke haze towards the northwest to affect Sarawak. On 24 August 2015, there was a deterioration in the air quality in several cities of Sarawak such as Sri Aman and Kuching with the API readings in these cities registering unhealthy levels. In the next few days, the occurrence of showers in Sarawak brought an improvement to the hazy conditions there. Satellite images depicting some of the hotspot activities over the ASEAN region in August 2015 are shown in Figs. 2A to 2E.

3.1    The sea surface temperatures (SSTs) in the tropical Pacific Ocean (SST) have continued to warm in August 2015. A strong El Niño currently prevails in the tropical Pacific Ocean.

3.2    The rainfall in the Southeast Asia region is showing a clear response to the El Niño development, with observed large-scale drier-than-normal conditions, in particular in the southern and eastern parts of the region. A consensus forecast based on international climate models and expert opinion suggests a high likelihood of the warming of the SST to continue. Further strengthening of El Niño conditions are likely in the coming months, and the El Nino is expected to prevail into early 2016.

3.3    Typically the impact of El Niño for the Southeast Asia region is drier than average rainfall conditions, especially for the southern parts of the ASEAN region during June to October. More locally-specific impact differs from place to place and for different seasons.

3.4    The ASEAN region is currently in the Southwest Monsoon season (June-September/early October), where the El Niño is known to have considerable impact (dryness) on the western part of the Maritime Continent. Thus with the current El Niño conditions, there is a high risk that the Sep-Oct-Nov season could experience extended periods of drier and warmer weather conditions in this part of Southeast Asia.