Category Archives: Fortnightly Weather Review

1.1    The Southwest Monsoon season prevailed in September 2015, with low level winds mainly blowing from the southeast or southwest. The monsoon rain band located close to the northern ASEAN region brought shower activities on most days to parts of the region. In contrast, dry weather conditions in the southern ASEAN region prevailed throughout September 2015.

1.2    Tropical Storm Vamco, which developed on 13 September 2015 over the South China Sea, made landfall south of Danang, Vietnam the next day. Vamco caused flooding and damages particularly to the agriculture and fisheries sectors in Vietnam. The Tropical Storm Vamco continued on its westward track and triggered floods across some provinces in Thailand before gradually dissipating on 18 September.

1.3    The prevailing El Niño conditions continued to have an impact on rainfall activities in the ASEAN region. Below-average rainfall was recorded across most parts of the southern ASEAN region. In the northern ASEAN region, near-average to below-average rainfall was received in the Mekong sub-region. The southern part of Philippines recorded above-average rainfall while below-average rainfall was received in the northern part of Philippines. The regional rainfall distribution for September 2015 is shown in Figure Fig. 1A.

2.1    In September, hotspot activities over the northern ASEAN region were generally subdued by the prevailing wet weather conditions. In contrast, the southern ASEAN region was affected by a prolonged transboundary haze situation in recent years. Persistent hotspot activities were observed especially in the fire-prone provinces of central and southern Sumatra, as well as in Kalimantan throughout the month.

2.2    In September 2015, moderate to dense smoke haze blanketed most parts of the central and southern Sumatra, and West and Central Kalimantan. On most days, the air quality readings in many parts of Sumatra including Jambi were in the hazardous range. Hazardous air quality readings were also reported in Palangkaraya in central Kalimantan and Pontianak in western Kalimantan on a number of days. Visibility was reduced to less than 1 km on most days in Jambi, Pekan Baru and Rengat in Sumatra and in Pontianiak and as the haze situation worsened.

2.3    The moderate to dense smoke haze from the fire-prone provinces in Sumatra and Kalimantan were carried by the prevailing winds to affect the region including Brunei Darussalam, Peninsular Malaysia, Sarawak, Singapore and southern Thailand. Some haze had also spread to the South China Sea and was blown by the prevailing winds to affect some islands in southern Philippines.

2.4    Parts of Peninsular Malaysia, East Malaysia and Singapore were affected by transboundary smoke haze since early September 2015. Air quality was in the Unhealthy and/or Very Unhealthy ranges on most days, and on a few days, the air quality entered into the Hazardous range which resulted in school closures, flight diversions or delayed flights amid poor visibility. On 25 September, the 24-hr PSI in Singapore hit a high of 322. On 26 September, visibility at the Subang Airport deteriorated to below 500 m and the airport was closed for several hours. Air quality readings in Port Klang, Shah Alam and Batu Muda also worsened to Very Unhealthy levels of 224-243 the next day morning.

2.3    In Kuching, Samarahan and Sri Aman, the Air Quality Index (AQI) ranged from ~68-~205, with most days in the Unhealthy to Very Unhealthy range between 9 and 28 September 2015. On 10 September, visibility at the Kuching International Airport deteriorated to below 800m and caused disruptions to flight operations and schedules. Satellite images depicting some of the hotspot activities over the ASEAN region in September 2015 are shown in Figs. 2A to 2E.

3.1    The sea surface temperatures (SSTs) in the tropical Pacific Ocean (SST) have increased further in September 2015. A strong El Niño currently prevails in the tropical Pacific Ocean.

3.2    Atmospheric conditions in the ASEAN region have been showing a clear response to the strong El Niño conditions. Large-scale drier-than-normal conditions have been observed particularly in the southern and eastern parts of the ASEAN region. A consensus forecast based on international climate models and expert opinions suggest the continuation of strong El Niño conditions into early-2016, with the possibility of further strengthening in the coming months.

3.3    Typically the impact of El Niño for the Southeast Asia region is drier than average rainfall conditions, especially in 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 region is now gradually transitioning from the Southwest Monsoon season (Jun-Sep/Oct) into the inter-monsoon period (Oct Nov). El Niño can still have a significant impact on the weather conditions (dryness) over the southern part of ASEAN region, in particular, the western part of the Maritime Continent. With the current El Niño conditions, there is still a risk that the prevailing Aug-Sep-Oct (ASO) season could experience extended periods of drier and warmer 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.

1.1    The Southwest Monsoon conditions in the region continued to prevail in July 2015. While the northern ASEAN region is in its wet season, and the monsoonal rainband continue to lie mostly between latitudes 10 and 15 degrees North, some parts of the region experienced drier than usual conditions. A shift of the monsoon rainband to the near-equatorial region on several days in mid-July 2015 brought shower activities to the southern ASEAN region, in particular over Peninsular and West Malaysia, Sumatra and Kalimantan. Dry weather conditions continue to persist in Java and the eastern archipelago of Indonesia.

1.2    On 5 July 2015, Tropical Storm Linfa made landfall over the northern Luzon Island of the Philippines, bringing heavy rainfall that resulted in floods and landslides in northern Luzon. Linfa continued on its northwestward track into the South China Sea before making landfall in the southern parts of Guangdong province, China.

1.3    Severe drought was experienced in Thailand due to a prolonged drier than usual weather in the months leading up to July. A respite to the drought situation arrived in mid-July 2015 with increased shower activities over Thailand. On the contrary, heavy monsoonal rain bands associated with Cyclone Komen brought widespread flooding to many parts of Myanmar around end-July 2015. More than 260,000 people across 12 of Myanmar’s 14 states were affected by severe floods.

1.4    The southern ASEAN region continued to receive lower than normal rainfall in July which could be partly due to the prevailing El-Nino conditions. For the northern ASEAN region, well-above normal rainfall was received in Myanmar and northern Philippines. Below-normal to near-normal rainfall was received for the rest of the northern ASEAN region. The regional rainfall distribution for July 2015 is shown in Fig. 1A.

2.1    In the northern ASEAN region, shower activities over most parts of the region helped to suppress hotspot activities.

2.2    In the southern ASEAN region, elevated hotspot activities were observed mainly in Riau and Jambi provinces of Sumatra since early-July 2015. Shower activities on several days in mid-July 2015 helped to subdue the hotspot activities. Around end-July 2015, a return of drier weather conditions saw an increase in burning activities, and smoke plumes were seen emanating from various hotspot clusters in Sumatra. Most of the fires were short-lived, and the region was not affected by significant transboundary haze.

2.3    In Kalimantan, there were persistent shower activities in the first half of July 2015. However by mid-July 2015, dry weather conditions emerged and contributed to an increase of hotspot activities in parts of Kalimantan. Moderate haze and smoke plumes were observed near the hotspots for the several days in the second half of July. Satellite images depicting some of the hotspot activities over the ASEAN region in July 2015 are shown in Figs. 2A to 2E.

3.1    The tropical Pacific Ocean’s sea-surface temperature (SST) continues to warm in July 2015. Both its atmosphere and ocean conditions are at moderate El Nino levels.

3.2    The atmospheric patterns over the tropical Pacific Ocean continue to support the El Niño pattern, including weakened trade winds and excess rainfall in the eastern tropical Pacific Ocean. International climate models and expert opinion predict a high likelihood (in excess of 80-90% chance) for this SST warming to continue into early-2016. Further strengthening of the El Niño is likely.

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

3.4    The region is now in the Southwest Monsoon season (June – September), where El Niño is known to have considerable impact (dryness) on the western part of the Maritime Continent. Thus with the current El Niño developing conditions, the upcoming Aug-Sep-Oct season faces risk of extended periods of drier and warmer conditions in this part of Southeast Asia.

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    Inter-Monsoon season, which is characterised by light wind and wet weather conditions, prevailed over the ASEAN region in May 2015. The northward migration of the monsoon trough during the period brought persistent shower activities over the northern ASEAN region.

1.2    Super Typhoon Noul, which developed in early May 2015 from a tropical depression in the western Pacific Ocean made landfall over Cagayan in northeastern Luzon Island in the Philippines on 10 May 2015. “Noul” continued to track northeast towards Okinawa, Japan before dissipating in the North Pacific Ocean.F

1.3    In southern ASEAN, wet weather conditions generally prevailed until mid-May. Due to the northward migration of the monsoon trough, the shower activities had gradually eased off by late May.

1.4    In May 2015, most parts of northern ASEAN region received less than 50% of normal rainfall. Most of the southern ASEAN region, except Java, received 50 – 75 % of normal rainfall. The regional rainfall distribution for May 2015 is shown in Fig. 1A.

2.1    Persistent shower activities prevailed in May 2015 over the ASEAN region. The hotspot activities were generally subdued, and there were no occurrences of significant transboundary haze during the review period

2.2    During periods of drier weather conditions in May 2015, isolated hotspots with localized smoke haze were observed on a few days. Satellite images depicting some of the hotspot activities over the ASEAN region in May 2015 are shown in Figs. 2A to 2D.

1.1    Inter-Monsoon conditions prevailed over the ASEAN region in April 2015. The gradual northward migration of the monsoon trough brought an increase of shower activities over most parts of ASEAN region, especially towards late-April.

1.2    In April 2015, less than 50% of normal rainfall was received in most parts of northern ASEAN region except northern Thailand and Luzon Island in the Philippines. In the southern ASEAN region, near-normal rainfall was received across most parts. Less than 75% of normal rainfall was received mainly over southern Peninsular Malaysia, northern Sumatra and northern Borneo. The regional rainfall distribution for April 2015 is shown in Fig. 1A.

2.1    In April 2015, there was a gradual reduction in hotspot activities over the northern ASEAN region due to increased shower activities in the region. Localised smoke haze and hotspot activities were observed in early-April especially in the northern parts of Lao PDR and Vietnam, as well as in areas around the border between Thailand and Myanmar. Towards the later part of April 2015, persistent shower activities further subdued hotspot activities in the northern ASEAN region

2.2    In the southern ASEAN region, hotspot activities were generally subdued by widespread shower activities that affected the region. Satellite images depicting some of the hotspot activities over the ASEAN region in April 2015 are shown in Figs. 2A to 2E.

1.1    In the last week of March 2015, weak to moderate Northeast Monsoon conditions gave way to Inter-Monsoon conditions, and prevailing winds gradually weakened to become light and variable. The traditional dry season in the northern ASEAN region continued to prevail in the first half of the month, with drier weather conditions experienced mostly over northern Thailand and Myanmar. By late march 2015, a return of showers activities brought some respite to the dry weather conditions experienced in the past few months in the near-equatorial and northern ASEAN regions.

1.2    In March 2015, less than 50% of normal rainfall was received in most parts of the northern ASEAN region while in parts of central Thailand, Lao PDR and Vietnam received more than 125% of normal rainfall. In the southern ASEAN region, below normal rainfall was recorded over Peninsular Malaysia, Sabah, Sarawak and Kalimantan. The regional rainfall distribution for March 2015 is shown in Fig. 1A.

2.1    In March 2015, hotspot activities over northern Thailand, Myanmar and Cambodia remained elevated under the prevailing dry weather conditions. Parts of Myanmar and the northern provinces of Thailand were shrouded in occasional moderate haze for an extended period of time. In particular, elevated levels of PM10 were reported in several provinces in northern Thailand, namely- Chiang Mai, Maehongsorn and Lampung. The haze situation in northern Thailand and Myanmar improved with an increase in shower activities in late March 2015.

2.2    In the southern ASEAN region, hotspot activities were generally subdued in most parts of March 2015. During brief periods of drier weather, isolated hotspots with localised smoke haze were observed in central Sumatra. Satellite images depicting some of the hotspot activities over the ASEAN region in March 2015 are shown in Figs. 2A to 2E.

2.3    The hotspot charts for March 2015 for

1. Cambodia, Myanmar, Thailand, Lao PDR and Vietnam;
2. Sumatra, Borneo and Peninsular Malaysia; and
3. Java, Sulawesi and the Philippines

are shown in Figs. 2F to 2H respectively

1.1    Northeast Monsoon conditions continued to prevail in February 2015. The northern ASEAN region is in the midst of the traditional dry season. Dry and warm weather conditions continued to prevail in the region interspersed with a few brief periods of shower activities. In the southern ASEAN region, a strengthening of the northeast monsoonal flow and the southward shift of the monsoon rain belt over the Java Sea areas brought dry weather conditions to Malaysia, Singapore and Sumatra but heavy rainfall over western Java, causing widespread flooding in Jakarta.

1.2    In February 2015, less than 50% of normal rainfall was received in the northern ASEAN region except in parts of northern Thailand and Lao PDR, where more than 125% of normal rainfall was received. In parts of the southern ASEAN region such as Peninsular Malaysia and Sumatra, less than 50 to 75% of normal rainfall was received. The regional rainfall distribution for February 2015 is shown in Fig. 1A.

2.1    In February 2015, hotspot activities continued to stay elevated under the prevailing drier weather, particularly over northern Thailand, Cambodia, Lao PDR and Myanmar. The northern provinces of Thailand were shrouded in slight to moderate haze for an extended period of time. Dense haze over a few provinces in northern Thailand such as Chiang Mai and Lampung experienced dense haze on a several days. Shower activities over the northern ASEAN region were brief and did not bring much relief to the haze situation.

2.2    In the southern ASEAN region, isolated hotspot activities emerged especially over central Sumatra and Peninsular Malaysia during periods of drier weather. Satellite images depicting some of the hotspot activities over the ASEAN region in February 2015 are shown in Figs. 2A to 2E.

1.1    Northeast Monsoon conditions prevailed in January 2015. In the northern ASEAN region, dry weather conditions continued to affect the Mekong Sub-region of Cambodia, Lao PDR, Myanmar, northern Thailand and Vietnam. In mid-January 2015, the monsoon rain-belt had moved south of the equator marking the onset of the dry phase of the Northeast Monsoon season in the southern ASEAN region. Generally cooler, drier and windy weather conditions were experienced in Sumatra, Peninsula Malaysia and Singapore while wet weather conditions were felt in Kalimantan, the Java islands as well as parts of Sabah and Sarawak in Malaysia. In the last week of January 2015, a monsoon surge brought heavy rains and caused floods in the states of Sabah and Sarawak in Malaysia.

1.2    On 13 January 2015, Typhoon “Mekkhala” developed over the Western Pacific Ocean, and continued its westward track afecting the eastern part of Luzon and Visayas in the Philippines a few days later. Typhoon “Mekkhala” made landfall near eastern Samar, the Philippines on 17 January 2015, and weakened rapidly into a tropical depression as it moved north-eastwards, dissipating over water on 21 January 2015 away from Luzon Islands.

1.3    In January 2015, less than 75% of normal rainfall was received in most parts of northern ASEAN except in northern Thailand and southern parts of Vietnam, where more than 125% of normal rainfall was received. In most parts of the southern ASEAN region, less than 100% of normal rainfall was received. The regional rainfall distribution for January 2015 is shown in Fig. 1A.

2.1    In January 2015, the dry weather conditions led to an escalation of hotspot activities in the northern ASEAN region where scattered to widespread hotspots were observed on most days, in particular in Cambodia, central and northeastern Thailand and Lao PDR. Slight to moderate smoke haze was also observed on several occasions during the period.

2.2    In the southern ASEAN region, hotspot activities were mostly subdued by cooler and occasionally windy conditions. During brief periods of drier weather, sporadic hotspots were observed over central Sumatra and Peninsular Malaysia. Satellite images depicting some of the hotspot activities over the ASEAN region in February 2015 are shown in Figs. 2A to 2E.

1.1    Moderate Northeast Monsoon season was established in the region in December 2014, bringing dry and cool weather to most parts of the Mekong Sub-region of Cambodia, Lao PDR, Myanmar, northern Thailand and Vietnam. In the southern ASEAN region, the prevailing rainy season affected most parts of the southern ASEAN region.

1.2    Super Typhoon ‘Hagupit’ which was the most intense tropical cyclone of the year, developed to the east of the Philippines in the last week of November 2014. It strengthened as it tracked westwards, making landfall over the provinces of Samar and Masbate in the Philippines on 6 and 7 December 2014 respectively. ‘Hagupit’ weakened rapidly after making landfall and dissipated rapidly over the South China Sea, southeast of Vietnam. On 29 December 2014, another Tropical Storm ‘Jangmi’ affected the Philippines, making landfall over Mindanao. ‘Jangmi’ tracked across the Philippines before dissipating over South China Sea. Both ‘Hagupit’ and ‘Jangmi’ affected up to a million people, and destroying hundreds of houses along their path.

1.3    On 13 January 2015, Typhoon “Mekkhala” developed over the Western Pacific Ocean, and continued its westward track afecting the eastern part of Luzon and Visayas in the Philippines a few days later. Typhoon “Mekkhala” made landfall near eastern Samar, the Philippines on 17 January 2015, and weakened rapidly into a tropical depression as it moved north-eastwards, dissipating over water on 21 January 2015 away from Luzon Islands.

1.4    During the second half of December 2014, the strengthening of north-easterly winds over the South China Sea, or a monsoon surge, affected the region on a few occasions. The monsoon surges brought wet and windy conditions to parts of the southern ASEAN region. Continuous heavy showers of rain fell over most parts of Peninsular Malaysia, and led to severe flooding in the eastern coastal States of Terengganu, Pahang, and Kelantan with around 250,000 people displaced from their homes. Several districts in Indonesia and southern Thailand were also affected by floods due to the several days of continuous rainfall.

1.5    In December 2014, many parts of the southern ASEAN region received more than 100% of normal rainfall with the exception of southern Sumatra and western Borneo where less than 100% of normal rainfall was received. In contrast, most parts of the northern ASEAN region such as Thailand, Myanmar and Cambodia received less than 50% normal rainfall. Many parts of the Philippines received more than 125% of normal rainfall due to the passage of Super Typhoon ‘Hagupit’ and Tropical Storm ‘Jangmi’. The regional rainfall distribution for December 2014 is shown in Fig. 1A.

2.   Review of Land/Forest Fires and Smoke Haze Situation