Category Archives: Regional Weather Review for Year 2017

March 10, 2017

Review of Regional Weather and Smoke Haze for Feb 2017

1. Review of Regional Weather Conditions in February 2017

1.1 The Northeast Monsoon conditions prevailed over the ASEAN region in February 2017. Dry weather conditions persisted over most areas of the Mekong sub-region, except over parts of Thailand and Cambodia where brief periods of showers were observed. During the month, the monsoon rain band was between the Equator and 15 S, and rainy weather conditions were experienced over most parts of the southern ASEAN region. The rainfall distribution for February 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 February 2017, rainfall was below-normal in parts of Myanmar, northern and central Thailand, Lao PDR and Cambodia. Rainfall was above-normal over most parts of Vietnam and the Philippines. In contrast, rainfall was mostly near-normal to above-normal in the southern ASEAN region. The percentage normal of rainfall for February 2017 is shown in Figure 2.

1.3 Most of the rainfall activities in February 2017 was concentrated between the the Equator and the region around Java, and Mindanao, the Philippines (Figure 1). In mid-February, a strong monsoon surge brought a strengthening of winds and enhanced rainfall activities over the southern ASEAN region. The heavy rainfall associated with the monsoon surge fell mainly over coastal areas of Sarawak and the Java Sea. During the second half of February, some parts of Java as well as Jakarta Indonesia, were affected by heavy rains and floods due to localised thunderstorm activities.

1.4 In February 2017, north-easterly winds prevailed over the northern ASEAN region while winds in the southern ASEAN region blew predominantly from the west or northwest. Figure 3 shows the average and anomalous winds at 5000 feet. During the month, winds from the northern and southern hemispheres converged between 5 S and 10 S, and westerly or south-westerly wind anomalies prevailed over the Java Sea and the eastern parts of the Maritime Continent. In addition, the occurrence of cyclonic circulation anomalies over the Western Pacific Ocean contributed to the above-normal rainfall over the Philippines.

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

1.5 The cool anomalies of the equatorial Pacific Ocean’s sea-surface temperature (SST) over the Niño 3.4 region weakened further but remained within the neutral (neither El Nino nor La Nina) thresholds. Most of the atmospheric conditions over the equatorial Pacific were in near average conditions, except for cloudiness and rainfall over the central and western tropical Pacific which remained indicative of weak La Niña conditions.

1.6 The Madden Julian Oscillation (MJO) was active and strong in February 2017 and is likely to have played a significant role on the rainfall over the tropical region during this period. In the first week of February 2017, the MJO was in Phase 4-5 and brought enhanced shower activities over the southern parts of Maritime Continent. In the second and third week of February 2017, the MJO strengthened and propagated through Phase 6-8, which contributed to less convective activities over the western Maritime Continent including parts of Sumatra and Peninsular Malaysia. The MJO continued its passage into Phase 1-2 towards the end of February 2017.

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 the Mekong Sub-region, hotspot activities persisted mainly in Thailand and Cambodia during the first half of February 2017. Visible smoke plumes and moderate haze were observed in parts of northern Cambodia on a few days. In the latter half of the month, brief periods of shower activities helped to prevent further escalations in hotspot activity over Cambodia. However, in Myanmar, there was a deterioration in the fire situation with the prevailing dry weather conditions, and led to an increase in the number of detected hotspots.

2.2 The hotspots in Myanmar were detected mainly along the Arakan ranges and near the borders between Myanmar and northern Thailand. Reduced visibility and elevated air quality readings were reported in some stations over northern Thailand on several days. In Mae Hong Son, the PM10 reading exceeded 150 ug/m3 (Unhealthy range) on 27 February 2017.
2.3 Hotspot activities in the southern ASEAN region remained largely subdued due to the prevailing wet weather conditions.

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

Fig. 5: NOAA-19 satellite image on 5 March 2017 shows scattered hotspots with smoke haze observed in central Thailand and northern Cambodia.

Fig. 6:NOAA-19 satellite image on 13 March 2017 shows scattered hotspots detected in parts of Myanmar.

Figure 7: NOAA-19 satellite image on 23 March 2017 shows elevated hotspot activities detected in northern Thailand. Fire hotspots in Cambodia and Vietnam were subdued due to shower activities.

Figure 8: NOAA-19 satellite image on 24 March 2017 shows few clusters of hotspots with smoke haze detected in Myanmar.

Figure 9: NOAA-19 satellite image on 24 March 2017 shows hotspot activities subdued over the southern ASEAN region due to wet weather conditions.

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

2.6 In February 2017, a high density of hotspots was observed in the northern ASEAN region, particularly over Myanmar, Thailand and Cambodia. A large number of hotspots persisted over the Myanmar-Thailand border between Naypyitaw, Myanmar and Mae Hong Son province Thailand. In Thailand, most of the hotspots were detected in the areas close to Kamphaeng Phet, Phetchabun and Sakon Nakhon provinces. In Cambodia, large clusters of hotspots persisted over the northern half of the country between Siem Reap and Mondulkiri. In the southern ASEAN region, the number of hotspots detected remained low.

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 climate models indicate the tropical Pacific will continue to remain at neutral levels but may warm gradually from March 2017 onwards. Given the observations and outlook, an extension of La Niña is the least likely scenario until mid-2017.

3.2 Few models suggest that the warming may reach El Niño levels again in 3Q 2017. However, as the seasonal prediction model outlooks of El Nino at this time of the year is known to have the least skill, a more confident assessment of El Niño risk will be available around mid-2017.

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 February 2017, the Indian Ocean Dipole (IOD) index increased slightly but continued to remain at neutral levels, as shown in Figure 13. International climate models forecast the IOD to remain neutral and would unlikely 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 13: Indian Ocean Dipole (IOD) index time series. The IOD index is at the neutral level for March 2017. (Source: Bureau of Meteorology).

February 17, 2017

Review of Regional Weather and Smoke Haze for Jan 2017

Print Version

1. Review of Regional Weather Conditions in January 2017

1.1 The prevailing Northeast Monsoon conditions continued into January 2017. Dry weather conditions interspersed with brief periods of showers prevailed over the Mekong sub-region. In southern Thailand and the Philippines, wet weather conditions prevailed. With the monsoon rain band over the equatorial region between 10 N and 15 S, most parts of the southern ASEAN region experienced wet weather conditions. The rainfall distribution for January 2017 is shown in Figure 1.

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

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

1.2 In January 2017, rainfall was above-normal over most parts of the northern ASEAN region except in Cambodia and the eastern parts of Thailand where rainfall was below-normal. In the southern ASEAN region, rainfall was near-normal to above-normal. The percentage normal of rainfall for January 2017 is shown in Figure 2.

1.3 The rainfall in January 2017 was distributed mainly across the equatorial region. Heavy rains affected parts of southern Thailand, Malaysia, southern Philippines and the surrounding region of Java Sea. In southern Philippines, a slow moving low-pressure system over the Mindanao and Visayas areas brought heavy rainfall to these areas. In addition, several monsoon surges, characteristic of the Northeast Monsoon season affected the region. Monsoon surges refer to the strengthening of winds over the South China Sea due to the intensification of high pressure system over northern China. In the first week of January, a monsoon surge brought heavy rains and caused widespread flooding in southern Thailand that affected over 12 provinces. Between 20 and 24 January, a second monsoon surge brought heavy rain showers that affected the near-equatorial region including the east coast of Peninsular Malaysia, Singapore and parts of central Sumatra.

1.4 In January 2017, northeasterly winds prevailed in the northern ASEAN region while northwesterly and westerly winds blew predominantly in the southern ASEAN region. The average and anomalous winds at 5000 feet are shown in Figure 3. Between the Equator and 10^oS, there were large-scale westerly anomaly winds over an area extending from the Indian Ocean to the Java Sea. In addition, the presence of two distinct cyclonic circulations due to the formation of low pressure systems in the Andaman Sea and in southern Philippines brought well-above normal rainfall to the region.

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

1.5 For the month, the equatorial Pacific Ocean’s sea surface temperature (SST) over the Niño 3.4 region was within neutral ENSO threshold values, and the atmospheric indicators such as the trade winds and cloudiness over the equatorial Pacific, indicated either weakening La-Niña or neutral conditions.

1.6 In the first half January 2017, the Madden Julian Oscillation (MJO) was weak or indiscernible and did not contribute significantly to the weather in the region. The MJO however, emerged from Phase 1 and progressed through Phase 2 to Phase 3 in the latter half of January. The passage of MJO through Phase 2 and 3 was likely to have enhanced the impact of monsoon surge which brought heavy rainfall over southern Thailand and east coast of Peninsular Malaysia between 20 and 24 January.

Figure 4: The MJO phase diagram for January 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 Mekong sub region, hotspot activities were relatively low in the first half of January 2017. A few contributing factors could be due to the presence of cloud cover, obscuring detection by satellites, and occurrence of showers activities over parts of the northern ASEAN region which could have helped to subdue hotspot activities in parts of the northern ASEAN region. In the second half of January, dry weather conditions in the region brought a significant increase in the number of hotspots, in particular over Thailand and Cambodia. Clusters of scattered hotspots persisted in parts of central Thailand and the northern half of Cambodia. In addition, localised smoke plumes were seen to emanate from some of the hotspots detected.

2.2 In the southern ASEAN region, most of the hotspots were detected in central Sumatra where brief periods of dry weather conditions were experienced in the first half of January 2017. Overall, the hotspot activities in the regioin remained largely subdued due to the prevailing shower activities.2.3 Satellite images depicting some of the hotspot activities over parts of the ASEAN region during January 2017 are shown in Figure 5 – Figure 9.

Fig. 5: NOAA-19 satellite image on 9 January 2017 shows hotspot activities over the Mekong sub-region were relatively inactive in the first half of January due to shower activities.

Fig. 6: NOAA-19 satellite image on 10 January 2017 shows isolated hotspots emerged over parts of central Sumatra during brief period of dry weather.

Figure 7: NOAA-19 satellite image on 20 January 2017 shows isolated hotspots began to emerge in Myanmar.

Figure 8: NOAA-19 satellite image on 28 January 2017 shows a cluster of scattered hotspots detected over northern Cambodia. Localised smoke plumes were observed to emanate from some of the hotspots.

Figure 9: NOAA-19 satellite image on 30 January 2017 shows hotspot activities subdued over Kalimantan due to shower activities.

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

2.5 In January 2017, there were several clusters of scattered hotspots detected in the northern ASEAN region (as shown in Figure 10). Most notably, a cluster of high density hotspots was detected in the northern half of Cambodia including the provinces of Preah Vihear, Kampong Thom, Kratie and Mondulkiri. Scattered hotspots were also detected in Myanmar, central Thailand and Lao PDR. In the southern ASEAN region, the overall number of hotspots detected remained low. Isolated hotspots were detected mainly in Sumatra, West Kalimantan and Sarawak.

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

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

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

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

3.1 Climate models from major climate centres project neutral ENSO conditions in the coming season until May 2017, and the weak cool anomalies over the Niño 3.4 region to gradually weaken by April 2017.

3.2 Typically, La Niña brings wetter-than-normal rainfall conditions to most parts of Southeast Asia, and has a less pronounced impact on the weather over the near-equatorial region during the Northeast Monsoon season. Locally-specific impact differs from place to place and for different seasons.

3.3 In January 2017, the Indian Ocean Dipole (IOD) continued to remain at neutral levels, as shown in Figure 13. International climate models forecast the IOD to be neutral and would unlikely 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 13: Indian Ocean Dipole (IOD) index time series. The IOD index is at the neutral level for January 2017. (Source: Bureau of Meteorology).