Category Archives: Regional Weather Review for Year 2017

January 19, 2018

Review of Regional Weather and Smoke Haze for Dec 2017

1. Review of Regional Weather Conditions in December 2017

1.1 In December 2017, Southeast Asia experienced northeast monsoon conditions with drier weather conditions over the northern ASEAN region, and rainy or wet weather conditions in the southern ASEAN region. Most of the rain during the month fell within the region bounded between 10oS and 10oN of the Equator. The most intense rain that fell during the month was over the central South China Sea and to the east of the Philippines. These areas coincided with the path of the tropical cyclones crossing the central South China Sea, north of Borneo after making landfall in the Philippines. The rainfall distribution for December 2017 is shown in Figure 1.

Figure 1: Daily average rainfall for the ASEAN region in December 2017. (Source: JAXA Global Satellite Mapping of Precipitation).

Figure 2: Percent of Normal Rainfall for December 2017. The rainfall data may be less representative for areas with a less dense rainfall network.

1.2 In the second half of December 2017, intensification of the high pressure system in northern Asia brought a monsoon surge or a sudden surge of cold winds over the South China Sea. As these strong northeasterly winds blew equatorward over the South China Sea, it gathered moisture and led to the development of persistent rain clouds over large parts of the equatorial region. The surges brought strong winds and spells of moderate to heavy rain to Borneo, Peninsular Malaysia and Singapore. In particular, the eastern coastal states of Peninsular Malaysia and northern coast of Borneo were affected by heavy rainfall and intense floods arising from the monsoon surges.

1.3 Above-normal rainfall was recorded in most parts of the northern ASEAN region except for the eastern parts of Cambodia and the southern parts of Laos and Vietnam where below-normal rainfall was received. Most parts of the southern ASEAN region received normal to above-normal rainfall. Figure 2 shows the percent of normal rainfall for December 2017.

figureNb

Figure 3: (Left) Historical storm track for Tropical Cyclone Dahlia. (Source: JAXA); (Right) NOAA-19 satellite image on 1 December 2017 shows Typhoon Dahlia, located south of Java.

Figure 4: Historical storm tracks for Typhoon Kai-Tak and Typhoon Tembin.

1.4 In December 2017, 3 tropical cyclones brought heavy rainfall and strong winds to the region. On 1 December, Tropical cyclone “Dahlia” (Figure 3) moved over the Indian Ocean, south of Java, bringing heavy rains to Java’s southern coast. On 14 December, a tropical depression (Figure 4) over the western Pacific Ocean, east of Cebu, the Philippines, intensified into Typhoon “Kai-Tak” and tracked over the South China Sea towards Peninsular Malaysia after making landfall in central Philippines. Heavy rain from the bands of “Kai-Tak” fell over the eastern coastal states of Peninsular Malaysia. As “Kai-Tak” dissipated over the South China Sea, another tropical depression over the western Pacific Ocean developed and tracked westwards and intensified into Typhoon “Tembin” over the South China Sea (Figure 4) before dissipating over water as it approached the southern Vietnam.

1.5 In December 2017, prevailing winds blew predominantly from the northeast or east in the northern ASEAN region and from the west or northwest in the southern ASEAN region. Strong anomalous westerly winds were recorded between 5o S and 10o N, extending from the Indian Ocean to the western Pacific Ocean due to the passage of typhoons “Kai-Tak” and “Tembin” in the South China Sea. Figure 5 shows the average and anomalous winds at 5000 feet.

figure3b

Figure 5: 5000 ft average winds (left) and anomaly (right) for December 2017.

1.6 During the month, sea surface temperatures (SSTs) over the Niño 3.4 region in the equatorial Pacific Ocean remained at La Niña values. The stronger than average trade winds and below-average cloudiness indicate La Niña conditions.

1.7 The Madden Julian Oscillation (MJO) was active throughout most of December 2017, propagating from a start phase of Phase 5, ending in Phase 2 towards the end of the month. The MJO however did not play a significant role in modulating the rainfall over the Southeast Asia regions. The rainfall was more likely modulated by the typhoons and monsoon surges in the region.

Figure 6: The MJO phase diagram for December 2017. The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or no signal exhibited. (Source: Bureau of Meteorology)

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

2.1 Dry weather conditions prevailed over the northern ASEAN region in the second half of December 2017. This led to an increase in the number of hotspots detected, in particular in parts of Thailand, Cambodia and Vietnam. There were no significant smoke plume or haze observed from these hotspots.

2.2 Wet weather conditions prevailed in the southern ASEAN region, which helped to subdue hotspot activities there. Satellite images of hotspots detected in the ASEAN region in December 2017 are shown in Figure 7 to 10.

Fig. 7: NOAA-19 satellite image on 27 Nov 2017 shows dry and fine weather conditions over most parts of the Mekong sub-region.

Figure 8: NOAA-19 satellite image on 28 Nov 2017 shows heavy thunderstorm activities in central Java associated with a low pressure system off the southern coast of Java.

Figure 9: NOAA-19 satellite image on 29 Nov 2017 shows widespread shower activities prevailed over many parts of the southern ASEAN region.

Figure 10: NOAA-19 satellite image on 29 Nov 2017 shows dry weather conditions over Myanmar.

2.3 The hotspot distribution and daily hotspot charts for December 2017 are shown in Figure 11, Figure 12 and Figure 13.

Figure 11: Figure 10: NOAA-19 hotspots distribution in December 2017.

Figure 12: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in December 2017.

Figure 13: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in December 2017.

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

3.1 Experts from International climate centers assessed that the tropical Pacific Ocean will continue to be cool and La Niña conditions would prevail until about March 2018.

3.2 The region is currently experiencing Northeast Monsoon conditions. Typically, for Southeast Asia, the impact from La Niña is wetter-than-normal rainfall conditions. For the weather over the near-equatorial region, the impact of La Niña is usually less pronounced during the Northeast Monsoon season (Dec – Mar) as compared to the Southwest Monsoon season (Jun – Sep).

3.3 In December 2017, the Indian Ocean Dipole (IOD) index remained at neutral levels (Figure 14). In the coming months, international climate models forecast the IOD to remain neutral and it is not likely to have a significant influence on the weather over the region for the next few months. The formation of IOD typically starts around May or June, and peaks between August and October before decaying rapidly between December and April.

Figure 14: Indian Ocean Dipole (IOD) index remained at neutral levels.

December 8, 2017

Review of Regional Weather and Smoke Haze for Nov 2017

Print Version

1. Review of Regional Weather Conditions in November 2017

1.1 In November 2017, Southeast Asia experienced inter-monsoon conditions in the first half of the month where the low level winds were generally light and variable in direction. A gradual strengthening of winds to blow predominantly from the northeast in the second half of November 2017 signalled the start of the Northeast Monsoon season. In the latter half of the month, the monsoon rain band was observed to shift southwards to lie between latitudes 10 ^o S and 10 ^o N. Most of the rainfall in November 2017 was recorded over the southern ASEAN region. The rainfall distribution for November 2017 is shown in Figure 1.

Fig. 1A: Daily average rainfall for the ASEAN region in November 2017. (Source: JAXA Global Satellite Mapping of Precipitation).

Figure 2: Percent of Normal Rainfall for November 2017. The rainfall data may be less representative for areas with a less dense rainfall network.

1.2 In the last week of November 2017, an intensification of a high pressure system in northern Asia led to a strengthening of northeast monsoon winds or a monsoon surge over the South China Sea. The surge brought prolonged moderate to heavy rainfall over southern Thailand and the north-eastern parts of Peninsular Malaysia. Widespread flooding was reported in Songkhla, Thailand, as well as in parts of Kelantan and Terengganu, Peninsular Malaysia.

1.3 In November 2017, rainfall was above normal in central Vietnam, southern Thailand and in the northern parts of the Philippines, and below normal in northern Thailand, Lao PDR and northern Vietnam. For the southern ASEAN region, normal to above-normal rainfall was recorded over most parts of the region. Figure 2 shows the percent of normal rainfall for November 2017.

Figure 3: Historical storm tracks for Typhoon “Damrey”. (Source: JAXA)

1.4 On 1 November 2017, a tropical depression developed to the west of Cebu, the Philippines. The system tracked westward over the South China Sea where it intensified into Typhoon “Damrey” on 3 November 2017. Typhoon “Damrey” brought rough seas and strong winds along its path and made landfall in central Vietnam on 4 November 2017. The typhoon brought heavy rains and strong winds, and caused widespread flooding over many provinces in central Vietnam before dissipating over land on 5 November 2017.

1.5 In November 2017, the prevailing winds over the northern ASEAN region blew mainly from the northeast or east while winds in the southern ASEAN region were generally light and blew from the west or northwest. Broad easterly wind anomalies were observed over the western Pacific Ocean while westerly or north-westerly wind anomalies extended from the Indian Ocean to the Java Sea. The presence of the monsoon trough, coupled with the convergence of winds and strong solar heating enhanced the convective activity over southern Southeast Asia. Figure 4 shows the average and anomalous winds at 5000 feet.

figure3b

Figure 4: 5000 ft average winds (left) and anomaly (right) for November 2017.

1.6 During the month, the equatorial Pacific Ocean’s sea-surface temperature (SST) over the Nino 3.4 region remained at borderline La Niña values, with the 3-month (Aug-Sep-Oct) Nino 3.4 index at -0.46. Atmospheric conditions, such as trade winds and cloudiness, over the equatorial Pacific were suggestive of weak La Niña conditions.

1.7 The Madden Julian Oscillation (MJO) was weak and non-discernible throughout most parts of November 2017. However, signs of Phase-4 MJO were observed in late-November which coincided with a monsoon surge. The development of Phase-4 MJO could have enhanced the intensity of the monsoon surge that affected the region.

Figure 5: The MJO phase diagram for November 2017. The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or no signal exhibited. (Source: Bureau of Meteorology)

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

2.1 With the gradual transition to the traditional dry season in the northern ASEAN region, an increase in hotspot activities was observed in the Mekong sub-region. The hotspots were detected mainly in the northern parts of the Mekong sub-region but there were no significant smoke haze emanating from these hotspots.

2.2 In the southern ASEAN region, the prevailing wet weather conditions helped subdue hotspot activities. Satellite images depicting some of the hotspot activities over parts of the ASEAN region during November 2017 are shown in Figure 6 – Figure 10.

Fig. 6: NOAA-19 satellite image on 4 Nov 2017 shows Typhoon “Damrey” over central Vietnam.

Fig. 7: NOAA-19 satellite image on 27 Nov 2017 shows dry and fine weather conditions over most parts of the Mekong sub-region.

Figure 8: NOAA-19 satellite image on 28 Nov 2017 shows heavy thunderstorm activities in central Java associated with a low pressure system off the southern coast of Java.

Figure 9: NOAA-19 satellite image on 29 Nov 2017 shows widespread shower activities prevailed over many parts of the southern ASEAN region.

Figure 10: NOAA-19 satellite image on 29 Nov 2017 shows dry weather conditions over Myanmar.

2.3 The hotspot distribution charts and daily hotspot charts for November 2017 are shown in Figure 11, Figure 12 and Figure 13 respectively.

Figure 11: Figure 10: NOAA-19 hotspots distribution in November 2017.

Figure 12: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in November 2017.

Figure 13: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in November 2017.

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

3.1 International climate centers have indicated that for the rest of 2017, the tropical Pacific Ocean will continue to cool, and that there would be at least a 60% chance of a weak La Niña developing by December 2017. Expert consensus have also projected that if a La Niña develops, the event is not expected to last beyond March 2018.

3.2 The region is currently experiencing Northeast Monsoon conditions. Typically, the impact from La Niña for Southeast Asia is wetter-than-normal rainfall conditions. The impact of La Niña on the weather over the near-equatorial region is usually less pronounced during the Northeast Monsoon as compared to the Southwest Monsoon (Jun – Sep).

3.2 In November 2017, the Indian Ocean Dipole (IOD) index was at neutral levels (Figure 14). In the coming months, models from international climate centres forecast the IOD to remain neutral and that it would have a significant influence on the weather in the region over the next few months. The formation of IOD typically starts around May or June, and peaks between August and October before decaying rapidly between December and April.

Figure 14: Indian Ocean Dipole Index Time Series

November 23, 2017

Review of Regional Weather and Smoke Haze for Oct 2017

Print Version

1. Review of Regional Weather Conditions in October 2017

1.1 Southwest Monsoon conditions continued to prevail in the first half of October 2017 and gradually transitioned to the inter-monsoon conditions in the second half of the month. The prevailing southeasterly to southwesterly winds over the ASEAN region gradually weakened to become more light and variable in direction.

Figure 1: Daily average rainfall for the ASEAN region in October 2017. (Source: JAXA Global Satellite Mapping of Precipitation)

Figure 2: Percent of Normal Rainfall for October 2017. The rainfall data may be less representative for areas with a less dense rainfall network.

1.2 During the month, most of the shower activities fell over the equatorial region between 5 S and 15 N. Figure 1 shows the rainfall distribution over the ASEAN region during the month of October 2017. Rainfall was below-normal over the eastern and southern parts of Thailand, and over the northern parts of Peninsula Malaysia and parts of East Malaysia. For most parts of the ASEAN region, rainfall was normal to above-normal. Figure 2 shows the percent of normal rainfall for October 2017.

1.3 The occurrence of several tropical cyclones in the first half of October 2017 brought heavy rainfall to some parts of the northern ASEAN region. Among these tropical cyclones, Tropical Depression ‘23W’ and Typhoon ‘Khanun’ brought heavy rainfall and strong winds to the Philippines and Vietnam. Tropical Depression ‘23W’ developed over the South China Sea on the 9 October 2017, which tracked west-northwest and made landfall over the northern coast of Vietnam on 10 October 2017. On 12 October 2017, Tropical Storm ‘Khanun’ developed over the east of Luzon in the Philippines. It tracked westwards and intensified into a typhoon over the South China Sea on the 15 October 2017, and continued to track westwards before making landfall over the southern coast of China. Typhoon ‘Khanun’ weakened and continued to track southwest bringing torrential rain and strong winds over northern Vietnam.

figureNb

Figure 3: Historical storm track for Tropical Depression 23W (left) and Typhoon Khanun (right). (Source: JAXA)

1.4 In October 2017, the prevailing winds over the southern ASEAN region were mainly from the southeast or southwest. In the northern ASEAN region, strong northeasterly winds extended from southern China to the Gulf of Thailand. Broad westerly wind anomalies were observed over the eastern parts of the equatorial Indian Ocean, northern half of Borneo and southern parts of the Philippines. A cyclonic wind anomaly was also observed over the western Pacific Ocean, east of Luzon Island, the Philippines. In the second half of October 2017, a gradual weakening of winds around the equatorial region was observed. Figure 4 shows the average and anomalous winds at 5000 feet.

Figure 4: 5000 ft average winds (left) and anomaly (right) for October 2017.

1.5 In October 2017, the equatorial Pacific Ocean’s sea-surface temperature (SST) over the Nino 3.4 region remained within the neutral range (neither El Niño nor La Niña) although a gradual cooling tendency towards La Niña conditions was observed. In addition, most atmospheric indicators showed La Niña-like conditions with slight strengthening of the trade winds and below-average cloudiness over the equatorial Pacific.

1.6 The Madden Julian Oscillation (MJO) was weak and non-discernible during the first week of October 2017. However, the MJO strengthened in the second week of the month and remained strong for the rest of October, transitioning from Phase 4 to Phase 7. The MJO was thus a major contributing factor to the rainfall over the ASEAN region. The MJO brought wetter-than-usual conditions over the ASEAN region in the second week of October 2017 and drier-than-usual conditions in the second half of the month.

Figure 5: The MJO phase diagram for October 2017 (green). The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or indiscernible. (Source: Bureau of Meteorology)

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

2.1 Hotspot activities in the northern ASEAN region were generally subdued in the first three weeks of October 2017 due to wet weather conditions. However, during the last week of the month, dry weather conditions prevailed over the region, with isolated hotspots detected mainly over Myanmar. In the southern ASEAN region, isolated hotspots were detected over West Kalimantan, northern Sumatra and southern Sumatra.
2.2 In the later part of October 2017, Sumatra and Kalimantan experienced periods of dry weather conditions. This contributed to a slight increase in the hotspot activities detected mainly over West Kalimantan, northern Sumatra and southern Sumatra. There were no smoke haze and plumes observed near the vicinity of the hotspots. The return of shower activities during the last few days of the month helped to alleviate the hotspot situation in the southern ASEAN region. Satellite images depicting some of the hotspot activities over parts of the ASEAN region in October 2017 are shown in Figures 6 to 10.

Fig. 6: NOAA-19 satellite image on 5 October 2017 shows shower activities over Kalimantan.

Fig. 7: NOAA-19 satellite image on 16 October 2017 shows Tropical Storm Talas located off the coast of Vietnam with extensive rain bands extending over northern Vietnam.

Figure 8: NOAA-19 satellite image on 26 October 2017 shows localised smoke plumes emanating from hotspots detected in West Aceh, Sumatra.

Figure 9: NOAA-19 satellite image on 30 October 2017 shows hotspots over central and southern Sumatra following an extended period of dry weather conditions.

Figure 10: NOAA-19 satellite image on 31 October 2017 shows localised smoke haze observed near hotspots detected in West Kalimantan.

2.3 The hotspot distribution charts and daily hotspot charts for October 2017 are shown in Figure 11, Figure 12 and Figure 13 respectively.

Figure 11: Figure 10: NOAA-19 hotspots distribution in October 2017.

Figure 12: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in October 2017.

Figure 13: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in October 2017.

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

3.1 Most models from major international climate centres have projected that the sea surface temperatures would continue to cool towards the end of 2017. During this period, the prevailing La Niña-like conditions are expected to be short-lived and persist until early 2018.

3.2 The region is currently experiencing Northeast Monsoon conditions. The impact of La Niña on the weather over the near-equatorial region is usually less pronounced during the Northeast Monsoon as compared to the Southwest Monsoon (Jun – Sep).

3.3 In October 2017, the Indian Ocean Dipole (IOD) index was neutral (Figure 14). In the coming months, international climate models forecast the IOD to remain neutral and it is not likely to have a significant influence on the weather over the region for the next few months. The formation of IOD typically starts around May or June, and peaks between August and October before decaying rapidly between December and April.

Figure 14: Indian Ocean Dipole (IOD) index time series. The IOD index is at the neutral level for October 2017. (Source: Bureau of Meteorology).

October 12, 2017

Review of Regional Weather and Smoke Haze for Sep 2017

Print Version

1. Review of Regional Weather Conditions in September 2017

1.1 In September 2017, Southwest Monsoon conditions prevailed over the ASEAN region, and the monsoon rain band migrated further south with most of the shower activities occurring over the equatorial region between 5^oS and 15^oN. The rainfall distribution for September 2017 is shown in Figure 1.

Figure 2: Daily Average Rainfall for September 2017. The rainfall data may be less representative for areas with a less dense rainfall network.

Figure 2: Percent of Normal Rainfall for September 2017. The rainfall data may be less representative for areas with a less dense rainfall network.

1.2 During the month, rainfall was below-normal over northern and central Thailand, while normal to above-normal rainfall prevailed for other parts of the northern ASEAN region. In contrast, for the southern ASEAN region, rainfall was mostly above-normal, particularly over Malaysia, Sumatra, Sulawesi and Papua. Figure 2 shows the percentage normal of rainfall for September 2017.

1.3 In September 2017, there were several tropical cyclones that brought heavy rainfall to Asia Pacific region. Among these tropical cyclones, only typhoon ‘Doksuri’ brought heavy rainfall and strong winds to the Philippines and Vietnam. “Doksuri” developed on 10 September 2017, and made landfall over Luzon, the Philippines before moving westwards over northern Philippines and into the South China Sea. ’Doksuri’ intensified into a typhoon as it continued to track west-northwestward over the South China Sea towards Vietnam. On 15 September 2017, Typhoon Doksuri made landfall near the north central regions of Vietnam. In addition to the torrential rain and strong winds, the coastal provinces of Vietnam experienced storm surges which accompanied the typhoon, Typhoon Doksuri weakened and dissipated shortly after making landfall.

Figure 3: Historical storm tracks for Typhoon Doksuri. (Source: JAXA)

1.4 The prevailing winds during September 2017 were predominantly from the southeast or southwest, particularly over the southern ASEAN region. In the northern ASEAN region, winds were light and blew from the south or southwest. Broad easterly wind anomalies were observed over the western Pacific Ocean and parts of the South China Sea. Figure 4 shows the average and anomalous winds at 5000 feet.

figure3b

Figure 4: 5000 ft average winds (left) and anomaly (right) for September 2017.

1.5 In September 2017, the equatorial Pacific Ocean’s sea-surface temperature (SST) over the Nino 3.4 region remained at neutral (neither El Niño nor La Niña) values. However, in recent weeks, there has been a gradual cooling of the sea surface temperatures, and the Nino 3.4 index dipped to negative values. However, atmospheric conditions, such as trade winds and cloudiness, over the equatorial Pacific have largely remained neutral.

1.6 The Madden Julian Oscillation (MJO) was weak and non-discernible in September 2017. Although there was a faint and brief MJO signal in Phase 3 in mid-September 2017, overall, the MJO did not have a significant influence on the weather conditions over the southern ASEAN region.during the month.

Figure 5: The MJO phase diagram for September 2017. The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or no signal exhibited. (Source: Bureau of Meteorology)

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

2.1 Hotspot activities in the northern ASEAN region were generally subdued in September 2017 due to wet weather conditions. In the southern ASEAN region, there were isolated or scattered hotspots detected mainly in southern Sumatra and West Kalimantan but the region was relatively wetter than usual during the month.

2.2 On a few days in the third week of September 2017, Kalimantan experienced a brief period of dry weather conditions. This led to an increase of hotspot activities in West Kalimantan on 22 and 23 September 2017, and localised smoke haze and plumes were seen emanating from some of the hotspots. The hotspots were short-lived as showers on subsequent days helped to bring an improvement to the hazy conditions. Satellite images depicting some of the hotspot activities over parts of the ASEAN region during September 2017 are shown in Figure 6 – Figure 10.

Fig. 6: NOAA-19 satellite image on 12 September 2017 shows isolated hotspots detected in southern Sumatra.

Fig. 7: NOAA-19 satellite image on 13 September 2017 shows hotspot activities in Kalimantan subdued by wet weather conditions.

Figure 8: NOAA-19 satellite image on 14 September 2017 shows Typhoon Doksuri approaching Vietnam.

Figure 9: NOAA-19 satellite image on 22 September 2017 shows scattered hotspots with slight to moderate smoke haze observed in West Kalimantan.

Figure 10: NOAA-19 satellite image on 29 September 2017 shows increased shower activities over the southern ASEAN region, particularly in Kalimantan and Java.

2.3 The hotspot distribution charts and daily hotspot charts for September 2017 are shown in Figure 11, Figure 12 and Figure 13 respectively.

Figure 11: Figure 10: NOAA-19 hotspots distribution in September 2017.

FigFigure 12: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in September 2017.

Figure 13: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in September 2017.

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

3.1 International climate centres have projected that the sea surface temperature would continue to cool in the second half of 2017. During this period, latest experts’ consensus favour neutral conditions or weak La Niña conditions.

3.2 Typically, El Niño brings drier-than-normal rainfall conditions to most parts of Southeast Asia during the Southwest Monsoon season. During La Niña events, the opposite, i.e. wetter-than-normal condition, normally occurs. Locally specific impact differs from place to place and for different seasons

3.2 In September 2017, the Indian Ocean Dipole (IOD) index remained in the neutral state (Figure 14). In the next few months, international climate models forecast the IOD to remain neutral.

Figure 14: Indian Ocean Dipole (IOD) index time series. The IOD index is at the neutral level for September 2017.

September 19, 2017

Review of Regional Weather and Smoke Haze for Aug 2017

Print Version

1. Review of Regional Weather Conditions in August 2017

1.1 Southwest Monsoon conditions continued to prevail in the region in August 2017. The monsoon rain band was located in the Northern Hemisphere, between latitude 5^oN and 20^oN, and brought extensive rainfall over the region. Heavy rain fell over the coastal regions of Myanmar and the northern parts of the Philippines. For the southern ASEAN region, dry weather conditions were experienced over parts of southern Sumatra and Java. The rainfall distribution for August 2017 is shown in Figure 1.

Figure 1: Daily average rainfall for the ASEAN region in August 2017. (Source: JAXA Global Satellite Mapping of Precipitation)

Figure 2: Percent of Normal Rainfall for August 2017. The rainfall data may be less representative for areas with low density of rainfall network.

1.2 In August 2017, rainfall was near-normal to above-normal over the northern ASEAN region except in Cambodia where rainfall was below-normal. In the southern ASEAN region, near-normal to above-normal rainfall prevailed except in southern Sumatra and parts of Java where rainfall was below-normal. Figure 2 shows the percent normal of rainfall for August 2017.

1.3 Two tropical storms – Hato and Pakhar were brewing in August 2017 over the western Pacific Ocean. Tropical Storm Hato developed to the northeast of the Philippines on the 20 August 2017. It tracked westwards and made landfall over the coast of southern China on the 23 August 2017. Tropical Storm Pakhar developed over the sea areas to the east of Luzon, the Philippines, on the 25 August 2017, and tracked north-westwards, crossing over northern Philippines before making landfall over the coast of southern China on the 27 August 2017. Both tropical storms brought heavy rains to Hong Kong and widespread shower activities over the northern ASEAN region.

figureNb

Figure 3: Historical storm tracks for Tropical Storm Hato (left) and Tropical Storm Pakhar (right). (Source: JAXA)

1.4 The prevailing winds in August 2017 were predominantly from the southwest in the northern ASEAN region, and from the southeast in the southern ASEAN region. Figure 3 shows the average and anomalous winds at 5000 feet. In the month of August 2017, anomalous northeasterly to easterly winds dominated over the South China Sea and the region east of the Philippines. Furthermore, an anomalous cyclonic circulation was observed over the South China Sea, east of Hainan Island, associated with the tropical storms Hato and Pakhar.

figure3b

Figure 4: 5000 ft average winds (left) and anomaly (right) for August 2017.

1.5 In August 2017, the equatorial Pacific Ocean’s sea-surface temperature (SST) over the Nino3.4 region was close to the El Niño Nino 3.4 index threshold. Most of the atmospheric indicators such as wind and cloudiness were fluctuating about the neutral values.

1.6 During the month, the Madden Julian Oscillation (MJO)1 was generally weak and non-discernible except for a brief period in Phase 2 towards the end of August 2017. Overall, the contribution by the MJO on the weather over the Maritime continent in August 2017 was not significant.

Figure 5: The MJO phase diagram for August 2017 (green). The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or indiscernible. (Source: Bureau of Meteorology)

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

2.1 In the first half of August 2017, the dry weather conditions led to an increase in hotspot activities in both the northern and southern ASEAN regions. On the 4 August 2017 and 6 August 2017, there were significant hotspot activities detected over Borneo and Sumatra respectively but no smoke haze was observed.

2.2 In the second half of August 2017, tropical storms Hato and Pakhar brought widespread showers to the region and subdued the hotspot activities in the northern ASEAN region. In contrast, some brief episodes of dry weather conditions over the southern ASEAN region led to an increase in hotspot activities, mostly in southern Sumatra and Borneo. Satellite images depicting some of the hotspot activities over parts of the ASEAN region in August 2017 are shown in Figures 6 – 9.

Figure 6: NOAA-19 satellite image on 6 Aug 2017 shows hotspot activities over Sumatra.

Figure 7: NOAA-19 satellite image on 4 Aug 2017 shows hotspot activities over West Kalimantan.

Figure 8: NOAA-19 satellite image on 27 Aug 2017. Tropical Storm Pakhar made landfall over southern China, inducing scattered showers over the Indochina.

Figure 9: NOAA-19 satellite image on 27 Aug 2017 show hotspots over southern and western Kalimantan.

2.3 The hotspot distribution and daily hotspot charts for August 2017 are shown in Figure 10 and Figure 11 and 12 respectively.

Figure 10: NOAA-19 hotspots distribution in August 2017.

Figure 11: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in August 2017.

Figure 12: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in August 2017.

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

3.1 Climate models from major climate centres indicate that the neutral (neither El Nino nor La Nina, conditions are expected to persist for the rest of 2017.

3.3 In the southern ASEAN region, occasional periods of drier weather can still be expected, and could lead to an occurrence of transboundary haze in the region. Hence, vigilance should be maintained for any escalation in hotspot activities in the fire-prone areas in the coming months.

3.4 In August 2017, the Indian Ocean Dipole (IOD) index was neutral (Figure 13). In the next few months, climate models from major climate centres project the IOD to remain neutral, with the possibility that a positive IOD may develop towards the end of 2017.

Figure 13: Indian Ocean Dipole (IOD) index time series. The IOD index was at neutral levels in August 2017. (Source: Bureau of Meteorology, Australia)

August 18, 2017

Review of Regional Weather and Smoke Haze for Jul 2017

Print Version

1. Review of Regional Weather Conditions in July 2017

1.1 Southwest Monsoon conditions continued to prevail in the region in July 2017. The monsoon rain band shifted further north and brought extensive rainfall over the region between latitudes 5^oN and 20^oN. Heavy rain fell over the coastal regions of Myanmar, Vietnam, the northern South China Sea and the northern parts of Philippines. For the southern ASEAN region, particularly over parts of Sumatra and Java, experienced dry weather conditions in the second half of the month. The rainfall distribution for July 2017 is shown in Figure 1.

Figure 1: Daily average rainfall for the ASEAN region in July 2017. (Source: JAXA Global Satellite Mapping of Precipitation).

Figure 2: Percentage of Normal Rainfall for July 2017. The rainfall data July be less representative for areas with low density of rainfall network.

1.2 In July 2017, rainfall was above normal over the northern ASEAN region. In the southern ASEAN region, near-normal to above-normal rainfall prevailed except in northern Sumatra, Sarawak, northern Kalimantan and parts of Java where rainfall was below-normal. Figure 2 shows the percentage normal of rainfall for July 2017.

1.3 Two tropical storms – Talas and Sonca formed over the South China Sea, east of Vietnam between 15 – 16 July 2017 and 21 – 25 July 2017 respectively. Tropical Storm Talas brought heavy rain and strong winds over the northern parts of Vietnam as it tracked westward on 16 July 2017. The storm dissipated the next day as it made landfall in northern Vietnam. Tropical Storm Sonca tracked westwards, similar to that of Talas except that Sanca’s impact was more widespread and brought heavy thunderstorms to parts of Thailand, Lao PDR and Vietnam.

figureNb

Figure 3: Historical storm tracks for Tropical Storm Talas (left) and Tropical Storm Sonca (right). (Source: JAXA)

1.4 The prevailing winds during July 2017 were predominantly from the southwest in the northern ASEAN region, and from the southeast or southwest in the southern ASEAN region. An anomalous cyclonic circulation associated with Tropical Storms Talas and Sonca was present over the South China Sea. Figure 4 shows the average and anomalous winds at 5000 feet.

figure3b

Figure 4: 5000 ft average winds (left) and anomaly (right) for July 2017.

1.5 In July 2017, the equatorial Pacific Ocean’s sea-surface temperature (SST) over the Nino3.4 region was warmer than average and close to the El Niño Nino 3.4 index threshold. However, these SST patterns over the tropical Pacific Ocean did not indicate developing El Niño conditions, and the atmospheric indicators such as cloudiness and winds over the equatorial Pacific were at neutral El Niño Southern Oscillation (ENSO) levels.

1.6 During the month, the Madden Julian Oscillation (MJO) was largely weak and non-discernible except for a few days around mid-July 2017 where the MJO strengthened as it emerged in Phase 3 bringing an increase in rainfall over the western Maritime continent. Overall, the contribution by the MJO on the weather over the Maritime continent in July 2017 was not significant.

Figure 5: The MJO phase diagram for July 2017. The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or no signal exhibited. (Source: Bureau of Meteorology)

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

2.1 In the first half of July 2017, hotspot activities in both the northern and southern ASEAN regions remained subdued due to wet weather conditions.

2.2 In the second half of July 2017, dry weather conditions set in over parts of Sumatra and Kalimantan. Significant hotspot activities were first observed in West Aceh Regency, Sumatra, and between 23 and 26 July 2017, hazy conditions were reported with visibility reduced to a low of 2-3 km during the period. With the occurrence of showers in the days following, 26 July 2017, the haze situation in West Aceh Regency improved. However, in the central and southern parts of Sumatra, the dry weather conditions in the last week of the month brought an increase in hotspot activities which persisted until the end of July 2017. Satellite images depicting some of the hotspot activities over parts of the ASEAN region during July 2017 are shown in Figure 6 – Figure 10.

Fig. 6: NOAA-19 satellite image on 5 July 2017 shows shower activities over Kalimantan.

Fig. 7: NOAA-19 satellite image on 16 July 2017 shows Tropical Storm Talas located off the coast of Vietnam with extensive rain bands extending over northern Vietnam.

Figure 8: NOAA-19 satellite image on 26 July 2017 shows localised smoke plumes emanating from hotspots detected in West Aceh, Sumatra.

Figure 9: NOAA-19 satellite image on 30 July 2017 shows hotspots over central and southern Sumatra following an extended period of dry weather conditions.

Figure 10: NOAA-19 satellite image on 31 July 2017 shows localised smoke haze observed near hotspots detected in West Kalimantan.

2.3 The hotspot distribution charts and daily hotspot charts for July 2017 are shown in Figure 11, Figure 12 and Figure 13 respectively.

Figure 11: Figure 10: NOAA-19 hotspots distribution in July 2017.

Figure 12: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in July 2017.

Figure 13: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in July 2017.

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

3.1 International climate centres have forecast that the observed warming of the tropical Pacific Ocean would subside and that neutral ENSO conditions are expected to prevail in the second half of 2017.

3.3 Despite the low likelihood of an El Niño developing, periods of dry weather condition can still be expected and could lead to the occurrence of transboundary haze in the region. Hence, vigilance should be maintained for any escalation in hotspot activities in the fire-prone areas in the coming months.

3.3 In July 2017, the Indian Ocean Dipole (IOD) index remained in the neutral state (Figure 14). In the next few months, international climate models forecast the IOD to remain neutral, with the possibility that a positive IOD may develop towards the end of the year.

Figure 14: Indian Ocean Dipole (IOD) index time series. The IOD index was at neutral levels in July 2017.

July 12, 2017

Review of Regional Weather and Smoke Haze for Jun 2017

Print Version

1. Review of Regional Weather Conditions in Jun 2017

1.1 Southwest Monsoon conditions became established over the ASEAN region in June 2017. The intensification of the sub-tropical high pressure system in the southern hemisphere gave rise to persistent southeasterly winds south of the equator and southwesterly winds north of the equator. During this period, the monsoon rain band was located between 5 S and 20 N. Heavy rainfall fell along the coastal areas of Myanmar as well as in the eastern parts of the Maritime Continent. The rainfall distribution for Jun 2017 is shown in Figure 1.

Figure 1: Daily average rainfall for the ASEAN region in Jun 2017. (Source: JAXA Global Satellite Mapping of Precipitation).

Figure 2: Percentage of Normal Rainfall for Jun 2017. The rainfall data Jun be less representative for areas with low density of rainfall network.

1.2 In June 2017, rainfall was above normal over Myanmar, parts of Vietnam and southern Philippines. In the southern ASEAN region, near-normal to above-normal rainfall prevailed over most parts of the region. However, rainfall was below-normal in northern and southern Sumatra. Figure 2 shows the percentage normal of rainfall for June 2017.

1.3 The prevailing winds during June 2017 were predominantly from the south or southwest in the northern ASEAN region. In the southern ASEAN region, prevailing winds blew from the southeast or south-southwest. There was no significant wind anomaly in the region except for an easterly anomaly over southern Philippines and a southerly anomaly over Myanmar, which could have contributed to the wetter-than-usual conditions in these areas. Figure 3 shows the average and anomalous winds at 5000 feet.

figure3b

Figure 3: 5000 ft average winds (left) and anomaly (right) for Jun 2017.

1.4 The equatorial Pacific Ocean’s sea-surface temperature (SST) over the Nino3.4 region continued to remain at neutral (neither El Niño nor La Niña) values. Atmospheric indicators such as cloudiness and winds over the equatorial Pacific were consistent with neutral El Niño Southern Oscillation (ENSO) conditions.

1.5 In June 2017, the Madden Julian Oscillation (MJO) was in Phase 3 for a few days and weakened rapidly in the subsequent days. The MJO remained in a non-discernible state until 9 June 2017. It emerged in Phase 8 and Phase 1 during the second and third week of June 2017 respectively before weakening again. There was no MJO signal until the end of June 2017. Overall, the MJO did not contribute significantly to the weather patterns over the Maritime Continent in June 2017.

Figure 4: The MJO phase diagram for Jun 2017. The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or no signal exhibited. (Source: Bureau of Meteorology)

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

2.1 In June 2017, hotspot activities in the northern ASEAN region were generally subdued due to the occurrence of increased rainfall brought by the onset of the Southwest Monsoon season.

2.2 In the southern ASEAN region, the number of hotspots detected remained low as wet weather conditions continued to persist, particularly over Sumatra and Kalimantan. Nonetheless, isolated hotspots with localised and short-lived smoke plumes were still observed in parts of Sumatra on a few days. Satellite images depicting some of the hotspot activities over parts of the ASEAN region during June 2017 are shown in Figure 5 – Figure 9.

Fig. 5: NOAA-19 satellite image on 3 June 2017 shows hotspot activities subdued by prevailing wet weather conditions in Kalimantan.

Fig. 6: NOAA-19 satellite image on 7 June 2017 shows isolated hotspots detected in northern and western parts of Sumatra.

Figure 7: NOAA-19 satellite image on 7 June 2017 shows increasing shower activities over the Mekong sub-region.

Figure 8: NOAA-19 satellite image on 23 June 2017 shows extensive shower activities and cloudy conditions over Sumatra.

Figure 9: NOAA-19 satellite image on 30 June 2017 shows wet weather conditions prevailing over Myanmar.

2.3 The hotspot distribution charts and daily hotspot charts for Jun 2017 are shown in Figure 10, Figure 11 and Figure 12 respectively.

Figure 10: Figure 10: NOAA-19 hotspots distribution in Jun 2017.

Figure 11: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in Jun 2017.

Figure 12: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in Jun 2017.

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

3.1 International climate centres indicate that the tropical Pacific Ocean will continue to warm gradually in the second half of 2017, and favors neutral ENSO conditions over El Niño.

3.2 Despite the low likelihood of an El Niño developing, periods of dry weather condition are expected and could lead to the occurrence of transboundary haze in the region.

3.3 Typically, El Niño brings drier-than-normal rainfall conditions to most parts of Southeast Asia, except over the near-equatorial region where the impact is less pronounced during the Northeast Monsoon season. During La Niña events, the opposite, i.e wetter-than-normal condition, normally occurs. Locally specific impact differs from place to place and for different seasons.

3.4 In June 2017, the Indian Ocean Dipole (IOD) has showed signs of transitioning into a positive IOD event although the IOD index continued to remain in the neutral state (Figure 13). In the next few months, based on international climate models, the IOD is forecast to remain neutral, with possibility that a positive IOD may develop toward the end of the year.

Figure 13: Indian Ocean Dipole (IOD) index time series. The IOD index is at the neutral level for Jun 2017. (Source: Bureau of Meteorology).

June 13, 2017

Review of Regional Weather and Smoke Haze for May 2017

Print Version

1. Review of Regional Weather Conditions in May 2017

1.1 May 2017, inter-monsoon conditions, characterised by light winds and afternoon shower activities, prevailed over the ASEAN region. During this period, rainfall activities increased over the northern ASEAN region. In the southern ASEAN region, drier weather conditions began to set in over the surrounding region of Java Sea. The rainfall distribution for May 2017 is shown in Figure 1.

Figure 1: Daily average rainfall for the ASEAN region in May 2017. (Source: JAXA Global Satellite Mapping of Precipitation).

Figure 2: Percentage of Normal Rainfall for May 2017. The rainfall data may be less representative for areas with low density of rainfall network.

1.2 In May 2017, most parts of the ASEAN region received near normal to above normal rainfall. In particular, rainfall was above normal over the eastern parts of the Philippines, southern Vietnam, Thailand, and over most parts of Sumatra and Kalimantan. Figure 2 shows the percentage normal of rainfall for May 2017.

1.3 The prevailing winds during May 2017 were predominantly from the southeast or south in the northern ASEAN region. In the southern ASEAN region, prevailing winds continued to remain light but blew from the southeast or southwest. An anomalous cyclonic circulation observed over the Andaman Sea brought enhanced rainfall activities over southern Thailand. Figure 3 shows the average and anomalous winds at 5000 feet.

Figure 3: 5000 ft average winds streamlines (left) and anomaly (right) for May 2017.

1.4 In Bay of Bengal, a low pressure system began to develop on 28 May and quickly strengthened into Cyclone Mora the next day. As the cyclone tracked northward toward Bangladesh, it brought strong winds and heavy rains over Arakan and Chin states in Myanmar. Cyclone Mora eventually made landfall in Bangladesh on 30 May and dissipated the next day.

1.5 The equatorial Pacific Ocean’s sea-surface temperature (SST) over the Nino3.4 region remained at neutral (neither El Niño nor La Niña) values. Atmospheric indicators such as cloudiness and winds over the equatorial Pacific were in the near average conditions.

1.6 In the first half of May 2017, the Madden Julian Oscillation (MJO) , in Phase 8 and Phase 1, did not have significant impact on the weather patterns in the Maritime Continent. The MJO subsequently weakened and was non-discernible during the third week of May. By the last week of May, the MJO redeveloped and emerged in Phase 2 and 3, which brought enhanced rainfall activities particularly over the surrounding region of Indian Ocean and Andaman Sea.

Figure 4: The MJO phase diagram for May 2017. The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or no signal exhibited. (Source: Bureau of Meteorology)

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

2.1 In the northern ASEAN region, isolated to scattered hotspots with localised smoke haze were observed in the northern half of Myanmar, Lao PDR and Vietnam in early May 2017. Increased shower activities over the northern ASEAN region in the second week of May 2017 signalled an end to the traditional dry season. The hotspot activities in the region were then generally subdued by shower activities.

2.2 In the southern ASEAN region, hotspot activities remained subdued due to wet weather conditions. Nonetheless, isolated hotspots were detected in parts of Sumatra on some days. Satellite images depicting some of the hotspot activities over parts of the ASEAN region during May 2017 are shown in Figure 5 – Figure 9.

Fig. 5: NOAA-19 satellite image on 3 May 2017 shows scattered hotspots and localised smoke haze in northern Lao PDR and Vietnam.

Fig. 6: NOAA-19 satellite image on 14 May 2017 shows scattered shower activities prevailed over the southern ASEAN region.

Figure 7: NOAA-19 satellite image on 15 May 2017 shows hotspot activities in the northern ASEAN region subdued by wet weather conditions.

Figure 8: NOAA-19 satellite image on 29 May 2017 shows enhanced rainfall activities in Myanmar due to the influence of Cyclone Mora over the Bay of Bengal.

Figure 9: NOAA-19 satellite image on 31 May 2017 shows prevailing wet weather conditions over Sumatra.

2.3 The hotspot distribution charts and daily hotspot charts for May 2017 are shown in Figure 10, Figure 11 and Figure 12 respectively.

Figure 10: Figure 10: NOAA-19 hotspots distribution in May 2017.

Figure 11: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in May 2017.

Figure 12: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in May 2017.

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

3.1 International climate centres are projecting a near equal chance of the El Niño Southern Oscillation (ENSO) remaining neutral and a chance of weak El Niño developing in the latter half of the year.

3.2 Should an El Niño develop, the conditions are expected to be weak and the impact over the Maritime Continent is unlikely to be significant.

3.4 In May 2017, the Indian Ocean Dipole (IOD) index continued to remain at neutral levels (Figure 13). In the next few months, based on international climate models, the IOD is forecast to remain neutral, with some chance that a positive IOD may develop toward the end of the year. The IOD is unlikely have a significant influence on the weather over the ASEAN region for the next few months.

Figure 13: Indian Ocean Dipole (IOD) index time series. The IOD index is at the neutral level for May 2017.

May 15, 2017

Review of Regional Weather and Smoke Haze for Apr 2017

Print Version

1. Review of Regional Weather Conditions in April 2017

1.1 Inter monsoon conditions, characterised by afternoon showers and winds that are generally light and variable in direction, prevailed over the region in April 2017. During the month, there was a gradual increase in rainfall over parts of the Mekong sub-region, mostly over Thailand, Cambodia and central Vietnam. Wet weather conditions continued to persist in the southern ASEAN region. The rainfall distribution for April 2017 is shown in Figure 1.

Figure 1: Daily average rainfall for the ASEAN region in April 2017. (Source: JAXA Global Satellite Mapping of Precipitation).

Figure 2: Percentage of Normal Rainfall for April 2017.

1.2 In April 2017, Myanmar, Vietnam and Lao PDR received near-normal to above-normal rainfall. However, over the eastern parts of Thailand and Lao PDR below-normal rainfall was recorded. Near-normal rainfall was received in northern parts of the Philippines while rainfall was above-normal in central and southern Philippines. In the southern ASEAN region, rainfall was near-normal except in northern Sumatra, east coast of Peninsular Malaysia and parts of Sarawak where below-normal rainfall was received . Figure 2 shows the percentage normal of rainfall for April 2017.

1.3 The prevailing winds during April 2017 were predominantly from the east or south-southwest over the northern ASEAN region. In the southern ASEAN region, prevailing winds were light but continued to blow mainly from the west or northwest. Similar to the conditions in March 2017, weak westerly wind anomalies were observed over the equatorial region between the Indian Ocean and the eastern parts of the Indonesian Archipelago. An anomalous cyclonic circulation over southern Thailand also contributed to enhanced rainfall activity in April 2017. Figure 3 shows the average and anomalous winds at 5000 feet.

figure3b

Figure 3: 5000 ft average winds streamlines (left) and anomaly (right) for April 2017.

1.4 On 13 April, a low pressure system developed in the Bay of Bengal and strengthened into Tropical cyclone Maarutha on 15 April 2017. Cyclone Maarutha made landfall in Myanmar the next day bringing widespread showers over most parts of Myanmar. This contributed to about 50 – 400 % of the long-term average rainfall in April over parts of western Myanmar. The cyclone dissipated quickly into a low pressure system on 17 April 2017.

1.5 The equatorial Pacific Ocean’s sea-surface temperature (SST) over the Nino3.4 region continued to warm but remained at neutral (neither El Niño nor La Niña) values. Most of the atmospheric indicators over the equatorial Pacific were in the near average conditions.

1.6 In the first half of April 2017, the Madden Julian Oscillation (MJO) was non-discernible. By late April 2017, while the MJO gradually strengthened, it remained at weak levels and did not have any significant influence on the weather patterns over the southern ASEAN region.

Figure 4: The MJO phase diagram for April 2017. The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or no signal exhibited. (Source: Bureau of Meteorology).

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

2.1 In the northern ASEAN region, an escalation of hotspot activities was observed mainly in Myanmar, Thailand and Lao PDR. During the first half of the month, widespread hotspots with smoke haze were detected along the western Arakan Ranges, eastern border of Myanmar, northern Thai provinces and northern parts of Lao PDR. Nonetheless, the passage of Tropical Cyclone Maarutha brought increased shower activities which helped alleviate the hotspot situation in Myanmar and northern Thailand.

2.2 In the early part of the second half of April 2017, brief periods of dry weather conditions led to an increase in the number of hotspots detected in northern Lao PDR. Moderate smoke haze was seen emanating from these hotspots. However, the fire hotspots were short-lived as they were subdued by onset of shower activities around end April 2017.2.3 In the southern ASEAN region, hotspot activities remained generally subdued due to the rainy weather in the region. Satellite images depicting some of the hotspot activities over parts of the ASEAN region during April 2017 are shown in Figure 5 – Figure 9.

Fig. 5: NOAA-19 satellite image on 10 April 2017 shows hotspots with smoke detected in various parts of Myanmar.

Fig. 6:NOAA-19 satellite image on 11 April 2017 shows moderate smoke haze emanating from a cluster of hotspots in Lao PDR.

Figure 7: NOAA-19 satellite image on 16 April 2017 shows Tropical Cyclone Maarutha which brought widespread rains that helped to subdue hotspots in Myanmar.

Figure 8: NOAA-19 satellite image on 26 April 2017 shows hotspot activities remained subdued in the southern ASEAN region.

Figure 9: NOAA-19 satellite image on 28 April 2017 shows a reduction in the number of hotspots detected in the Mekong sub-region due to increased shower activities.

2.4 The hotspot distribution charts and daily hotspot charts for April 2017 are shown in Figure 10, Figure 11 and Figure 12 respectively.

Figure 10: Figure 10: NOAA-19 hotspots distribution in April 2017.

Figure 11: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in April 2017.

Figure 12: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in April 2017.

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

3.1 Most models from major climate centres indicate the tropical Pacific Ocean will continue to gradually warm in the next 6 months. Forecasts suggest El Niño conditions being slightly favoured over neutral conditions from July-August-September.

3.2 However, the seasonal prediction model outlooks of El Niño at this time of the year are the least skillful all year round, a more confidence assessment of El Niño risk would be available from June onwards.

3.4 In April 2017, the Indian Ocean Dipole (IOD) index has increased slightly from previous month but continued to remain at neutral levels (Figure 13). In the next few months, based on international climate models, the IOD is forecast to remain neutral, with some chance that a positive IOD may develop later in the year. The IOD is unlikely have a significant influence on the weather over the ASEAN region for the next few months.

Figure 13: Indian Ocean Dipole (IOD) index time series. The IOD index is at the neutral level for April 2017. (Source: Bureau of Meteorology).

April 10, 2017

Review of Regional Weather and Smoke Haze for Mar 2017

Print Version

1. Review of Regional Weather Conditions in March 2017

1.1 The Northeast Monsoon conditions in the region gave way to inter-monsoon conditions in the second half of March 2017. During the month, there was a gradual increase of shower activities over parts of the Mekong sub-region, particularly over Thailand, Cambodia and central Vietnam was observed while over most parts of the southern ASEAN region, wet weather conditions continued to prevail. The rainfall distribution for March 2017 is shown in Figure 1.

Figure 1: Daily average rainfall for the ASEAN region in March 2017. (Source: JAXA Global Satellite Mapping of Precipitation).

Figure 2: Percentage of Normal Rainfall for March 2017. The rainfall data may be less representative for areas with low density of rainfall network

1.2 In March 2017, rainfall was near to above-normal over most parts of the northern ASEAN region, except in parts of Myanmar, Cambodia and southern Vietnam where below-normal rainfall was received. Likewise in most parts of the Philippines, near- to above-normal rainfall prevailed with most of the rainfall affecting the Mindanao area. In the southern ASEAN region, rainfall received was mostly near to above-normal, and in the second half of March 2017, parts of West Java and Peninsular Malaysia were affected by floods due to the occurrence of heavy thunderstorm activities on some days. Figure 2 shows the percentage normal of rainfall for March 2017.

1.3 The prevailing winds during the month were predominantly from the north-east or east over the northern ASEAN region, and from the west or northwest over the southern ASEAN region. In the second half of March 2017, there was a gradual weakening of winds over the ASEAN region around and north of the Equator. Westerly wind anomalies prevailed over the equatorial region between the Indian Ocean and the eastern parts of Indonesian Archipelago. The anomalous convergence observed over the northern parts of Borneo and southern Philippines could have contributed to above-normal rainfall over those areas. Figure 3 shows the average and anomalous winds at 5000 feet.

figure3b

Figure 3: 5000 ft average winds streamlines (left) and anomaly (right) for March 2017.

1.4 The cool anomalies of the equatorial Pacific Ocean’s sea-surface temperature (SST) over the Niño3.4 region further weakened towards neutral (neither El Niño nor La Niña) values, and most of the atmospheric indicators over the equatorial Pacific were in the near average conditions.

1.5 In early March 2017, the Madden Julian Oscillation (MJO) progressed through Phase 3 to Phase 4 in early March 2017, and this was a contributing factor to the increased rainfall received over the Indonesian Archipelago. The strength of the MJO gradually weakened towards mid-March 2017, and did not have a significant influence on the rainfall in the second half of the month.

Figure 4: The MJO phase diagram for March 2017. The MJO phase diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or no signal exhibited. (Source: Bureau of Meteorology)<

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

2.1 In March 2017, the hotspot activities in the northern ASEAN region remained active under the prevailing dry weather conditions. Large clusters of hotspots were detected in Myanmar and northern Thailand compared to February 2017. Most of the hotspots and areas of smoke haze were detected close to the border of Myanmar and Thailand, in the provinces of Mae Hong Son, Chiang Rai and Kamphaeng Phet. In the second half of March 2017, there was a further deterioration in the air quality in northern Thailand, and the PM10 readings exceeded 150ug/m³ (Unhealthy range) on several days in Mae Hong Son and Chiang Rai provinces. In Lao PDR, a high density of hotspots was detected in Xiangkhoang and Xaignabouri pronvinces. On the other hand, there was an increase in shower activities in Cambodia during the month which helped to ease the hotspot situation there.

2.2 In contrast, hotspot activities in the southern ASEAN region remained low and were mostly subdued due frequent shower activities in the region.

2.3 Satellite images depicting some of the hotspot activities over parts of the ASEAN region during March 2017 are shown in Figure 5 – Figure 9.

Fig. 5: NOAA-19 satellite image on 3 March 2017 shows widespread hotspots with smoke haze in parts of Myanmar.

Fig. 6:NOAA-19 satellite image on 14 March 2017 shows slight to moderate smoke haze over parts of northern Thailand.

Figure 7: NOAA-19 satellite image on 14 March 2017 shows occurrence of shower activities which has helped to subdue the hotspot activities over the southern ASEAN region.

Figure 8: NOAA-19 satellite image on 28 March 2017 shows scattered hotspots with smoke haze in Myanmar.

Figure 9: NOAA-19 satellite image on 31 March 2017 shows more occurrence of shower activities over the Mekong sub-region.

2.4 The hotspot distribution charts and daily hotspot charts for March 2017 are shown in Figure 10, Figure 11 and Figure 12 respectively.

Figure 10: Figure 10: NOAA-19 hotspots distribution in March 2017.

Figure 11: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam and Myanmar in March 2017.

Figure 12: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia in March 2017.

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

3.1 Most models from major climate centres indicate the tropical Pacific Ocean will continue to gradually warm over the next 6 months, and there is an increasing chance that weak El Niño conditions could develop in the second half of 2017.

3.2 As the seasonal prediction model outlooks of El Niño at this time of the year is known to have the least skill, a more confidence assessment of El Niño risk would be available around mid-2017 onwards.

3.4 In March 2017, the Indian Ocean Dipole (IOD) index was at neutral levels (Figure 13). In the next few months, based on international climate models, the IOD is forecast to remain neutral and it would unlikely have a significant influence on the weather over the ASEAN region. The formation of IOD typically starts around May or June, and peaks between August and October before decaying rapidly between December and April.

Figure 13: Indian Ocean Dipole (IOD) index time series. The IOD index is at the neutral level for March 2017. (Source: Bureau of Meteorology).