Subseasonal Weather Outlook and Review

1.1    Southwest Monsoon conditions continued to prevail in August 2016, with prevailing winds in the region blowing from the southeast or southwest. In early-August, Tropical Storm Nida made landfall over parts of Cagayan province, Philippines bringing scattered showers there before steering westward toward Guangdong province, China.

1.2    During the first half of August 2016, the monsoon rain belt persisted in the northern ASEAN region and brought widespread showers particularly over coastal areas of Myanmar and north-western parts of Philippines. Drier weather conditions were experienced across most parts of the southern ASEAN region.

1.3    In the second half of August, with the southward migration of the monsoon rain belt towards the equatorial region, there was an increase in rainfall observed over most parts of the southern ASEAN region.

1.4    For August 2016, near-normal to above-normal rainfall was received in the Mekong sub-region. In the Philippines, near-normal to above-normal rainfall prevailed in the northern and southern parts, while the central parts received below-normal rainfall. In the southern ASEAN region, near-normal rainfall was received in most parts of the near-equatorial region, except in central Sumatra and West Kalimantan where below-normal rainfall prevailed. Southern Sumatra and Java received above-normal rainfall. The regional rainfall distribution for August 2016 is shown in Figure Fig. 1A.

2.1    In August 2016, shower activities persisted on most days over the northern ASEAN region. This helped to subdue hotspot activities there.

2.2    Drier weather conditions in first half of August led to an escalation of hotspot activities over central Sumatra and West Kalimantan. Hotspots detected in central Sumatra were mostly localised, and slight hazy conditions were observed to have spread to the Strait of Malacca on a few days. In Kalimantan, widespread hotspot activities in excess of 100 hotspots with smoke haze were observed on a few days, particularly over West Kalimantan in mid-August 2016.

2.3    In the second half of August, an increase in shower activities over Kalimantan helped to ease the fire situation there. Showers fell over most parts of Sumatra, except in central Sumatra, where dry weather conditions with isolated hotspot activities were observed. The haze situation in Riau, central Sumatra deteriorated rapidly between 25 and 26 August 2016 and persisted until 29 August 2016 under dry weather and strong winds conditions. Moderate to dense smoke haze from the fires in Riau were blown by the southwesterly to westerly winds over the Strait of Malacca to central Peninsular Malaysia and Singapore, where the air quality deteriorated to Unhealthy levels.

2.4    The haze situation improved by 29 August 2016 with the return of shower activities over central Sumatra for the next few days. Hotspot activities over parts of the ASEAN region during August 2016 are shown in Figures 2A – 2E.

3.   Status of El Niño/La Niña

1.1    Southwest Monsoon conditions continued to prevail in August 2016, with prevailing winds in the region blowing from the southeast or southwest. In early-August, Tropical Storm Nida made landfall over parts of Cagayan province, Philippines bringing scattered showers there before steering westward toward Guangdong province, China.

1.2    During the first half of August 2016, the monsoon rain belt persisted in the northern ASEAN region and brought widespread showers particularly over coastal areas of Myanmar and north-western parts of Philippines. Drier weather conditions were experienced across most parts of the southern ASEAN region.

1.3    In the second half of August, with the southward migration of the monsoon rain belt towards the equatorial region, there was an increase in rainfall observed over most parts of the southern ASEAN region.

1.4    For August 2016, near-normal to above-normal rainfall was received in the Mekong sub-region. In the Philippines, near-normal to above-normal rainfall prevailed in the northern and southern parts, while the central parts received below-normal rainfall. In the southern ASEAN region, near-normal rainfall was received in most parts of the near-equatorial region, except in central Sumatra and West Kalimantan where below-normal rainfall prevailed. Southern Sumatra and Java received above-normal rainfall. The regional rainfall distribution for August 2016 is shown in Figure Fig. 1A.

2.1    In August 2016, shower activities persisted on most days over the northern ASEAN region. This helped to subdue hotspot activities there.

2.2    Drier weather conditions in first half of August led to an escalation of hotspot activities over central Sumatra and West Kalimantan. Hotspots detected in central Sumatra were mostly localised, and slight hazy conditions were observed to have spread to the Strait of Malacca on a few days. In Kalimantan, widespread hotspot activities in excess of 100 hotspots with smoke haze were observed on a few days, particularly over West Kalimantan in mid-August 2016.

2.3    In the second half of August, an increase in shower activities over Kalimantan helped to ease the fire situation there. Showers fell over most parts of Sumatra, except in central Sumatra, where dry weather conditions with isolated hotspot activities were observed. The haze situation in Riau, central Sumatra deteriorated rapidly between 25 and 26 August 2016 and persisted until 29 August 2016 under dry weather and strong winds conditions. Moderate to dense smoke haze from the fires in Riau were blown by the southwesterly to westerly winds over the Strait of Malacca to central Peninsular Malaysia and Singapore, where the air quality deteriorated to Unhealthy levels.

2.4    The haze situation improved by 29 August 2016 with the return of shower activities over central Sumatra for the next few days. Hotspot activities over parts of the ASEAN region during August 2016 are shown in Figures 2A – 2E.

3.   Status of El Niño/La Niña