Category Archives: Regional Weather Review for Year 2016

1.1    Northeast Monsoon conditions prevailed in December 2016. These conditions brought dry weather conditions interspersed with brief periods of showers to most parts of the northern ASEAN region. On the other hand, with the gradual southward migration of the monsoon rain band, the Northeast Monsoon brought wet weather conditions to the southern ASEAN region. The rainfall distribution for December 2016 is shown in Figure 1.

1.2    For December 2016, above-normal rainfall was recorded in southern Thailand, Vietnam and the Philippines while rainfall was below-normal in Myanmar, central Thailand, parts of Lao PDR and northern Vietnam. In the southern ASEAN region, rainfall was near-normal in most regions except in central Sumatra and western Java, where below-normal rainfall was recorded. The percentage normal of rainfall for December 2016 is shown in Figure 2.

1.3    The rainfall in December 2016 was distributed mainly in the equatorial region between 10N and 15S with several areas affected by heavy rainfall. A few northeast monsoon surges in December 2016 brought heavy rains to southern Thailand, central and southern parts of Vietnam and the east coast of Peninsular Malaysia. In addition, the presence of a low pressure system over the South China Sea in mid-December 2016 brought well above normal rainfall to the central and southern parts of Vietnam.

1.4    Over the Western Pacific Ocean, Typhoon Nock-Ten was first categorised as a tropical storm on 22 December 2016. It intensified further and tracked west-north-westward toward central Philippines before it made landfall on the eastern coast near Catanduanes Island on 25 December 2016. The typhoon then tracked westward and brought heavy rains and strong winds to the regions of Bikon and Calabarzon in central Philippines. ”Nock-Ten” moved over the South China Sea on 26 December and rapidly weakened into a tropical depression the next day.

1.5    In December 2016, the average and anomalous winds at 5000 feet (as in Figure 3), showed that north-easterly winds prevailing in the northern ASEAN region while westerlies prevailed in the southern ASEAN region. In the equatorial region of South China Sea, a cyclonic circulation was observed off the west coast of Sarawak and Sabah. This was due to the formation of Borneo vortices on some days in December, a feature which is typical during the Northeast Monsoon. The anomaly wind chart suggests that the anomalous circulation off the coast of southern Thailand is likely to be the primary cause of the well-above normal rainfall received in that region. The easterly anomaly brought below normal rainfall to most parts of the northern ASEAN region. Large-scale and persistent westerly anomaly winds observed across the equatorial region between 5 N and 10 S inhibited the incursion of the prevailing north-easterly flow across the equatorial region, contributing to the reduction of shower activities over Sumatra and parts of Java.

1.6    In December 2016, the equatorial Pacific Ocean’s sea surface temperature (SST) over the Nino 3.4 region was near weak La Niña threshold values. However, the atmospheric variables, such as trade winds and cloudiness over the equatorial Pacific, showed conditions that were more consistent with neutral ENSO conditions.

1.7    In December 2016, the Madden Julian Oscillation (MJO) was weak or indiscernible and is unlikely to have significantly influenced the weather over the region.

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

3.   Status of El Niño/La Niña and Indian Ocean Dipole

1.1    Inter monsoon conditions prevailed in the first half of November 2016. During this period, there was a gradual migration of the monsoon rain band from the northern ASEAN region to the near-equatorial region. In the Mekong sub-region, rainfall decreased gradually as the month progressed, and in the second half of the month, dry weather conditions were observed to have set in over the region. In contrast, wet weather conditions prevailed in the southern ASEAN region, particularly over Indonesia.

1.2    Over the Western Pacific Ocean, a tropical depression that developed to the southeast of central Philippines on 23 November 2016 intensified into Tropical Storm Tokage and made landfall over central Philippines on 25 November 2016. “Tokage’s” passage through the Philippines was brief as it northeast and moved over the South China Sea before dissipating over water on 27 November 2016. “Tokage” brought heavy rainfall and strong winds of up to 102km/h to areas along its path.

1.3    The Northeast Monsoon season onset in the ASEAN region in late November 2016. Between 28 and 30 November, the region experienced a monsoon surge episode where cold and strong northeasterly winds from a high pressure system over northern China surged into the South China Sea bringing widespread showers to the surrounding region, including Sarawak and the eastern coastal areas of Peninsular Malaysia.

1.4    For November 2016, above-normal rainfall was received in parts of the Mekong sub-region including Myanmar, north-eastern Thailand, Lao PDR and Vietnam. For the Philippines, near-normal to above-normal rainfall prevailed. Below-normal to near-normal rainfall prevailed over most parts of the southern ASEAN region including southern Thailand, Malaysia, Singapore, Brunei and Indonesia The regional rainfall distribution for November 2016 is shown in Fig. 1A.

2.1    In November 2016, hotspot activities in both the northern and southern ASEAN region remained largely subdued.

2.2    The Inter monsoon conditions in November 2016 brought an increase of rainfall over the southern ASEAN region, and the showers contributed to keep the hotspot activities over Sumatra and Kalimantan low. In the northern ASEAN region, hotspot activities were generally subdued on most days of the month and as the weather started to become drier, increase in hotspot activities were observed over parts of the Mekong sub-region towards the end of November 2016 with the onset of the Northeast Monsoon. Satellite images depicting some of the hotspot activities over parts of the ASEAN region during November 2016 are shown in Fig. 2A – Fig. 2E

3.   Status of El Niño/La Niña

1.1    Southwest Monsoon conditions prevailed on most days in October 2016 and the winds were blowing mostly from the west over most of the ASEAN region. In October 2016, there was a gradual increase of shower activities over the southern ASEAN region, and wetter than usual weather conditions were experienced in Java due to the warmer than usual sea surface temperatures over the eastern Indian Ocean. In contrast, the northern ASEAN region experienced less rainfall with dry weather conditions beginning to set in over parts of the region.

1.2    On 16 October, Typhoon Sarika made landfall and brought strong winds and heavy rains over central Luzon, the Philippines before tracking west-northwestward toward Hainan Island. This was followed by the passage of Super Typhoon Haima, which struck the northern tip of Luzon, the Philippines on 19 October 2016. Super Typhoon Haima moved to the northwest over the South China Sea and continued to steer toward southern China. The influence of both typhoons brought moderate to heavy rainfall parts of Indonesia, Peninsular Malaysia, Singapore, and Borneo Island as well.

1.3    Towards the end of October 2016, the region gradually transitioned from Southwest Monsoon conditions to Inter-Monsoon conditions. For October 2016, the Philippines and most parts of the Mekong sub-region received near-normal to above-normal rainfall. In the southern ASEAN region, near-normal rainfall prevailed over most parts of the near-equatorial region. Above-normal rainfall continued to prevail over Kalimantan, Java and the eastern parts of Indonesia Archipelago. The regional rainfall distribution for October 2016 is shown in Fig. 1A.

2.1    In October 2016, hotspot activities in both the northern and southern ASEAN region were largely subdued due to the prevailing wet weather conditions.

2.2    In early and mid-October 2016, there were brief periods of dry weather conditions over Sumatra and Kalimantan respectively. There was an increase in the number of hotspots, particularly in the western parts of central Sumatra and central Kalimantan. While smoke plumes were observed to emanate from some of the hotspots, the hotspot activities were localised and short-lived. The return of shower activities at the end of the brief dry periods helped to suppress the hotspot activities in Sumatra and Kalimantan. Satellite images depicting some of the hotspot activities over parts of the ASEAN region during October 2016 are shown in Fig. 2A – Fig. 2E

3.   Status of El Niño/La Niña

1.1    Southwest Monsoon conditions continued to prevail in September 2016, and the prevailing winds in the region blew mainly from the southwest or west. The monsoon rain belt was north of the Equator between latitudes 5 N and 15 N on most days in September 2016.

1.2    During the review period, showers affected most parts of the northern ASEAN region. On 12 September 2016, Tropical Depression “Rai”, which developed over the South China Sea, east-northeast of Ho Chi Minh City, made landfall in central Vietnam. “Rai” brought heavy rainfall to the Mekong sub-region, in particular over Vietnam and northern Thailand, causing the rivers to break its banks which led to severe flooding and loss of 12 lives. Over the southern ASEAN region, it was generally wet with occasional brief periods of dry weather conditions. This wetter than normal conditions is atypical of the traditional dry season of the southern ASEAN region in September 2016.

1.3    For September 2016, most parts of the northern ASEAN region except Cambodia and southern Vietnam recorded near-normal to above-normal rainfall. In the southern ASEAN region, near-normal rainfall was recorded in Malaysia, Brunei Darussalam and most parts of Sumatra. Above-normal rainfall prevailed over large areas of the Indonesian Archipelago, including southern Sumatra, Kalimantan and Java. The regional rainfall distribution for September 2016 is shown in Fig. 1A.

2.1    In September 2016, shower activities in the northern ASEAN region continued to subdue the hotspot activities there. For the southern ASEAN region, hotspot activities in the near-equatorial region were mostly subdued due to the higher than usual shower activities in the region.

2.2    In mid-September 2016, the influence of Super Typhoon Meranti over the western Pacific Ocean brought drier weather conditions over parts of Kalimantan. This led to an escalation of hotspot activities in West Kalimantan where more than 100 hotspots were detected between 12 and 14 September 2016. Visible smoke plumes and haze were observed mainly in West Kalimantan over the two days. The dry weather conditions were short-lived and an improvement in the hotspot and haze situation was experienced in the subsequent days as shower activities returned to Kalimantan.

2.3    In the last week of September 2016, the brief periods of dry weather conditions in parts of Sumatra brought an increase in hotspot activities but there were no significant smoke plumes or haze observed in the vicinity of the hotspots. Hotspot activities over parts of the ASEAN region during September 2016 are shown in Fig. 2A – Fig. 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

1.1    Southwest Monsoon conditions prevailed in July 2016, and the low level winds in the region blew predominantly from the southeast or southwest. The monsoon rain belt was over the northern ASEAN region in particular in the first half of July 2016 which brought increased shower activities to the northern ASEAN region. In the southern ASEAN region during this period, dry weather conditions were experienced. In the second half of July 2016, with the southward migration of the monsoon rain belt to the near-equator region, several parts of the southern ASEAN region including Indonesia, Malaysia and Singapore experienced wet weather conditions.

1.2    Typhoon Nerpatak, the first typhoon in 2016 over the Western Pacific region, was categorised as a tropical depression on 2 July 2016, east of the Philippines. It intensified into a super typhoon on 6 July 2016 as it tracked north-west towards Taiwan. While Typhoon Nerpatak did not make landfall in the ASEAN region, its rainbands brought widespread showers and strong winds to the northern parts of ASEAN region.

1.3    For July 2016, near-normal to above-normal rainfall was received in most parts of the northern ASEAN region. For the southern ASEAN region, the southern and eastern parts of the Indonesia Archipelago received well above-normal rainfall while areas including Malaysia, Sumatra and Kalimantan received near-normal to above-normal rainfall. The regional rainfall distribution for July 2016 is shown in Figure Fig. 1A.

2.1    In July 2016, it rained on most days for both the northern and southern ASEAN regions. In early July 2016, a brief period of dry weather conditions in parts of the southern ASEAN region led to an increase in hotspot activities over Sumatra. Smoke plumes were observed to emanate from some of the hotspots detected. Nonetheless, the hotspots were mostly short-lived and were mainly due to localised burning activities.

2.2    An increase in shower activities in the latter half of July 2016 brought a reduction to the number of hotspots detected over Sumatra and Kalimantan. There was no occurrence of transboundary smoke haze in July 2016. Some of the hotspot activities in the ASEAN region during July 2016 are shown in Figures 2A – 2E.

3.   Status of El Niño/La Niña

1.1    The Southwest Monsoon season onset in June 2016 with prevailing winds over the region blowing mostly from the southeast or southwest. Showers affected most parts of the southern ASEAN region, particularly over Java and its surrounding areas.

1.2    While shower activities affected many parts of the ASEAN region in the first three weeks of June 2016, dry weather conditions were experienced, in particular over the southern ASEAN region in the last week of June 2016.

1.3    For June 2016, most parts of the northern ASEAN region except Cambodia and Lao PDR received near-normal to above-normal rainfall. In the southern ASEAN region, above-normal rainfall was received over Peninsular Malaysia, Kalimantan and Java. The regional rainfall distribution for June 2016 is shown in Figure Fig. 1A.

2.1    In June 2016, hotspot activities remained largely subdued in both northern and southern ASEAN regions due to persistent wet weather conditions. In the last week of June 2016, the dry weather conditions experienced in the region contributed to a slight increase in hotspot activities in Sumatra. There was no occurrence of transboundary smoke haze in June 2016. Satellite images in Figure 2A – 2E show shower activities over various parts of the ASEAN region in June 2016.

3.   Status of El Niño/La Niña

1.1    Inter Monsoon conditions prevailed in May 2016 and shower activities returned to most parts of the ASEAN region as El Niño conditions in the equatorial Pacific Ocean continued to further weaken in May 2016.

1.2    Diurnal shower activities and light wind conditions prevailed on most days in both the southern and northern ASEAN regions. Around the end of May 2016, the Inter Monsoon conditions gradually transitioned to the Southwest Monsoon conditions, and a strengthening of winds over the South China Sea was observed. Shower in the region were gradually becoming less active over the Java Sea as the monsoon rain belt migrated further north.

1.3    For May 2016, most parts of the southern ASEAN region received near-normal rainfall except in parts of Kalimantan and Java Island where above-normal rainfall was received. In the northern ASEAN region, less than 100% of the normal rainfall was received mainly in Thailand, Cambodia and Lao PDR. The regional rainfall distribution for May 2016 is shown in Figure Fig. 1A.

2.1    Isolated hotspot activities with localised smoke haze were observed in the northern parts of Mekong sub-region and in parts of Peninsular Malaysia, in particular in early-May. An increase in the occurrence of showers in the rest of May 2016 helped to subdue hotspot activities in the ASEAN region. There was no significant transboundary haze situation.

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

1.1    Weak Northeast Monsoon conditions prevailed in March 2016 with winds that were light and from the northeaster on most days in March 2016. The monsoon rain belt continued to lie south of the equator. Most of the shower activities fell mostly over areas south of the equator while warm and dry weather conditions persisted over areas in the southern ASEAN region north of the equator, in particular over Peninsular Malaysia and Singapore.

1.2    Drought conditions affected several parts of the northern ASEAN region, and were particularly severe in northern Thailand, central and south Vietnam. Persistent warmer than usual temperatures were experienced in countries such as Thailand, Malaysia and Singapore. The northern states of Peninsular Malaysia, such as Chu Ping, Alor Star and Ipoh experienced very high temperatures on several consecutive days where the highest daily maximum temperatures ranged between 37 and 39 degrees Celsius.

1.3    Large scale drier than usual weather conditions were observed across many parts of ASEAN region in March 2016. In particular, significantly below-normal rainfall, i.e. less than 50% of normal rainfall, was received over areas north of the equator including northern ASEAN, Malaysia, Singapore, northern Sumatra and eastern Kalimantan. An exception was in the western coastal areas of Kalimantan where near-normal rainfall was received. The regional rainfall distribution for March 2016 is shown in Figure Fig. 1A.

2.1    Hotspot activities in Sumatra and Kalimantan were generally subdued by shower activities in March 2016. However, isolated hotspots with localised smoke plumes were detected in some parts of Peninsular Malaysia and Sabah such as central Pahang and Beaufort, Sabah due to drier than usual weather conditions there.

2.2    In the northern ASEAN region, hotspot activities remained elevated in March 2016 due to the prevailing dry weather conditions. The fires were particularly active along the borders between Myanmar and Thailand near Maehongsorn and Kanchanaburi provinces, as well as in northern Lao PDR and eastern Cambodia. Visible smoke plumes were seen emanating from these hotspot regions on a number of days. Hazy conditions and elevated PM10 readings exceeding 150ug/m3 were reported in Maehongsorn, Thailand.

3.   Status of El Niño/La Niña