Subseasonal Weather Outlook and Review

1.1    Inter Monsoon conditions characterised by light winds afternoon shower activities, particularly in the near-equatorial region prevailed in April 2016. In the northern ASEAN region, dry weather conditions persisted in the first half of April but there was a gradual increase of shower activities by late April 2016. Similar conditions were experienced in Peninsular Malaysia, Sabah and East Kalimantan. For parts of Sumatra and West Kalimantan, it was generally wet weather on most days of the month.

1.2    The drier and warmer than usual weather conditions which started since March 2016 continued in April 2016. Prolonged dry weather conditions affected many parts of the ASEAN region including Peninsular Malaysia, Philippines and countries in the Mekong Sub-region. High temperatures were also experienced in Thailand and Peninsular Malaysia where the maximum temperatures were reported to have exceeded 40 degrees Celsius in parts of Thailand. On 28 April 2016, the maximum temperature in Maehongsorn reached 44.3 degrees Celsius while in Peninsular Malaysia, maximum temperatures of between 35 to 39.2 degrees Celsius were reported in parts of the Malaysian States of Selangor, Perlis and Pahang.

1.3    1.3 For April 2016, most of the areas north of the equator including the northern ASEAN region, Peninsular Malaysia and Sabah received less than 100% of normal rainfall. Normal to above-normal rainfall were recorded in Sumatra, Kalimantan and the islands of Java. The regional rainfall distribution for April 2016 is shown in Figure Fig. 1A.

2.1    The fire-prone provinces of Sumatra and Kalimantan experienced wet weather conditions on most days in April 2016, and the showers helped to subdue the hotspot activities there. On the contrary, in parts of Peninsular Malaysia and Sabah, the drier than usual weather conditions contributed to the occurrence of localised hotspots and smoke haze on several days. In Beaufort, Sabah, for example, localized burning led to a deterioration of air quality where the Air Pollution Index (API) reached a high of 308 on 4 April 2016. On a few days around 22 April 2016, smoke haze from localized peat fires in Kuala Langat and Sepang in Selangor, Peninsular Malaysia affected the parts of Selangor including Shah Alam and Cheras where API readings were in the Unhealthy range for a few hours.

2.2    In the northern ASEAN region, with dry weather conditions persisting in the first half of April 2016, the hotspot activities continued to be high. Scattered hotspots and smoke haze were observed in the northern parts of Thailand, Lao PDR, as well as over the ranges west of Nakhon Sawan province and in parts of Cambodia. PM10 concentration levels in Chiang Mai, Chiangrai and Maehongsorn exceeded 120ug/m3 on several days in April 2016.

2.3    An increase in shower activities in the northern ASEAN region in the latter half of April 2016 helped to ease the haze situation in the Mekong Sub-region, which also brought a reduction to the number of hotspots detected.

3.   Status of El Niño/La Niña

1.1    Inter Monsoon conditions characterised by light winds afternoon shower activities, particularly in the near-equatorial region prevailed in April 2016. In the northern ASEAN region, dry weather conditions persisted in the first half of April but there was a gradual increase of shower activities by late April 2016. Similar conditions were experienced in Peninsular Malaysia, Sabah and East Kalimantan. For parts of Sumatra and West Kalimantan, it was generally wet weather on most days of the month.

1.2    The drier and warmer than usual weather conditions which started since March 2016 continued in April 2016. Prolonged dry weather conditions affected many parts of the ASEAN region including Peninsular Malaysia, Philippines and countries in the Mekong Sub-region. High temperatures were also experienced in Thailand and Peninsular Malaysia where the maximum temperatures were reported to have exceeded 40 degrees Celsius in parts of Thailand. On 28 April 2016, the maximum temperature in Maehongsorn reached 44.3 degrees Celsius while in Peninsular Malaysia, maximum temperatures of between 35 to 39.2 degrees Celsius were reported in parts of the Malaysian States of Selangor, Perlis and Pahang.

1.3    1.3 For April 2016, most of the areas north of the equator including the northern ASEAN region, Peninsular Malaysia and Sabah received less than 100% of normal rainfall. Normal to above-normal rainfall were recorded in Sumatra, Kalimantan and the islands of Java. The regional rainfall distribution for April 2016 is shown in Figure Fig. 1A.

2.1    The fire-prone provinces of Sumatra and Kalimantan experienced wet weather conditions on most days in April 2016, and the showers helped to subdue the hotspot activities there. On the contrary, in parts of Peninsular Malaysia and Sabah, the drier than usual weather conditions contributed to the occurrence of localised hotspots and smoke haze on several days. In Beaufort, Sabah, for example, localized burning led to a deterioration of air quality where the Air Pollution Index (API) reached a high of 308 on 4 April 2016. On a few days around 22 April 2016, smoke haze from localized peat fires in Kuala Langat and Sepang in Selangor, Peninsular Malaysia affected the parts of Selangor including Shah Alam and Cheras where API readings were in the Unhealthy range for a few hours.

2.2    In the northern ASEAN region, with dry weather conditions persisting in the first half of April 2016, the hotspot activities continued to be high. Scattered hotspots and smoke haze were observed in the northern parts of Thailand, Lao PDR, as well as over the ranges west of Nakhon Sawan province and in parts of Cambodia. PM10 concentration levels in Chiang Mai, Chiangrai and Maehongsorn exceeded 120ug/m3 on several days in April 2016.

2.3    An increase in shower activities in the northern ASEAN region in the latter half of April 2016 helped to ease the haze situation in the Mekong Sub-region, which also brought a reduction to the number of hotspots detected.

3.   Status of El Niño/La Niña