Category Archives: Fortnightly Weather Review

CR58

October 13, 2014

Review of Regional Weather and Smoke Haze for Sep 2014

1. Review of Regional Weather Conditions in September 2014

1.1 Weak Southwest Monsoon conditions continued to prevail in the ASEAN region in September 2014 with low level winds blowing mostly between the southeast or southwest.

1.2 The Northwestern Pacific Ocean experienced a total of 6 tropical cyclones in September 2014. Two of these tropical cyclones, namely Typhoon “Kalmaegi” and Tropical Storm “Fung-Wong” affected the northern ASEAN region. Typhoon “Kalmaegi” which developed to the northeast of Palau on 10 September 2014 intensified rapidly as it tracked westwards across Luzon, the Philippines before eventually making landfall over Hainan island on 16 September 2014. Typhoon “Kalmaegi” brought strong winds and heavy rainfall to the areas along its path which resulted in several dozens of flight delays and cancellations in Hong Kong and China, and floods in parts of Philippines and Vietnam. Tropical Storm “Fung-Wong” developed to the west of the Philippines on 17 September 2014. It tracked northwestwards and made landfall over northern Luzon in the Philippines and intensified as it continued its track northwest over the South China Sea. “Fung-Wong” weakened as it made landfall over Shanghai on 23 September 2014.

1.3 The presence of tropical cyclones in the surrounding region enhanced convective activities in the northern ASEAN region with 125% of normal rainfall received in some parts of the Philippines, Laos PDR and Thailand. In contrast, the southern ASEAN region experienced mostly dry weather conditions interspersed with occasional shower activities for September 2014. Many areas in the southern ASEAN region received less than 50% of normal rainfall. The regional rainfall pattern for September 2014 is shown in Fig. 1A.

Fig. 1A: Percentage of Normal Rainfall for September 2014. The rainfall data may be less representative for areas with low density of rainfall network.

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

2.1 In the northern ASEAN region, hotspot activities were generally subdued due to wet weather conditions. Sporadic hotspots were detected in Thailand and Vietnam during occasional brief periods of drier weather.

2.2 In the southern ASEAN region, dry weather conditions, in particular in the southern half of Sumatra and Kalimantan led to escalations in hotspot activities during the month. Persistent hotspots with smoke plumes and moderate to dense smoke haze were observed mostly over southern Sumatra and Kalimantan on several days. The widespread smoke haze from these fires led to a deterioration in the air quality and visibility in parts of central and southern Sumatra, and Kalimantan. In addition, the smoke haze was transported by the prevailing low level winds to affect Peninsular and East Malaysia and Singapore on several occasions in September 2014, with air quality in the unhealthy range on some days. Satellite images depicting some of the hotspot activities in the ASEAN region in September 2014 are shown in Figs. 2A to 2E.

Fig. 2A: NOAA-18 satellite picture on 13 September 2014 showing hotspot activities and smoke haze in southern Sumatra.

Fig. 2B: NOAA-18 satellite picture on 17 September 2014 showing moderate to dense smoke haze in parts of Kalimantan.

Figure 2C: NOAA-18 satellite picture on 24 September 2014 showing widespread smoke haze emanating from clusters of hotspots in southern Kalimantan.

Fig. 2D: NOAA-18 satellite picture on 25 September 2014 showing widespread moderate to dense smoke haze in southern Sumatra.

Fig. 2E: NOAA-18 satellite picture on 26 September 2014 showing widespread smoke haze in southern Sumatra.

2.3 The hotspot charts for September 2014 for

Cambodia, Myanmar, Thailand, Lao PDR and Vietnam;
Sumatra, Borneo and Peninsular Malaysia;

are shown in Figs. 2F to 2G respectively

Fig. 2F: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam, Myanmar for September 2014.

Fig 2G: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia for September 2014.

3. Status of El Niño/La Niña

3.1 The tropical Pacific Ocean is currently in neutral (neither El Niño nor La Niña) conditions. However, renewed signs of warming of sea surface temperatures there have been observed in September (Figure 3A) following the easing in July (Figure 3B). With most global climate models forecasting the continued warming of the tropical Pacific Ocean in the coming months (Figure 3C), a weak El Niño is still likely to develop towards the end of the year. There is now about 60% chance of El Niño occurring in October-November-December season (Figure 3D) and this is down from 70-80% stated in earlier predictions.

3.2 Typically the impact from El Niño for the Southeast Asia region is drier than average rainfall conditions, especially for the southern and eastern parts during June to October (Figure 3E). More locally-specific impact differs from place to place and for different seasons. As we are entering the inter-monsoon season in October, and with the possibility of a weak El Niño developing in the last quarter of 2014, the risks of occasional extended periods of drier and warmer conditions cannot yet be ruled out.

September 13, 2014

Review of Regional Weather and Smoke Haze for Aug 2014

Print Version

1. Review of Regional Weather Conditions in August 2014

1.1 Southwest Monsoon conditions continued to prevail in August 2014. In the northern ASEAN region of Cambodia, Laos PDR, Myanmar, Thailand, Vietnam and the Philippines, the traditional rainy season. For the southern ASEAN region, generally wet weather conditions with brief periods of drier weather conditions prevailed.

1.2 One typhoon affected the north-western Pacific Ocean during this month. Typhoon “Halong” developed to the east of the Philippines, tracked towards northwards and made landfall in Japan on 8 August. The presence of Typhoon “Halong” enhanced convective activities in the equatorial region which resulted in the development of extensive rain clouds, bringing wet weather to most parts of the southern ASEAN region during the first half of the month.

1.3 The presence of the monsoon trough over the northern ASEAN region during the first fortnight of October 2014 enhanced convective activities there and brought more than 100% of normal rainfall to parts of the Philippines, Laos PDR, Thailand and Vietnam.

1.4 During the month, most parts of the ASEAN region received more than 75% of normal rainfall with the exception of Kalimantan and western Java where less than 50% of normal rainfall was received. The regional rainfall pattern for August 2014 is shown in Figure 1A.

Fig. 1A: Percentage of Normal Rainfall for August 2014. The rainfall data may be less representative for areas with low density of rainfall network.

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

2.1 Shower activities have helped to subdue hotspot activities in most parts of the southern ASEAN region during the month. However, elevated hotspot activities were detected mainly over Borneo and Sumatra during periods of drier weather conditions. Scattered hotspots with smoke haze were detected mainly over western and central Kalimantan. In Sumatra, isolated hotspots with localized smoke plumes were detected mainly in the southern half of Sumatra.

2.2 In the northern ASEAN region, the prevailing rainy season continued to keep hotspot activities subdued. Sporadic hotspots were detected mainly in Vietnam during occasional brief dry periods. Satellite images depicting some of the hotspot activities over the ASEAN region in August 2014 are shown in Figs. 2A to 2E.

Fig. 2A: NOAA-18 satellite picture on 03 August 2014 showing moderate smoke haze from scattered hotspots in west Kalimantan.

Fig. 2B: NOAA-18 satellite picture on 04 August 2014 showing smoke plumes emanating from some of hotspots in Riau.

Figure 2C: NOAA-18 satellite picture on 16 August 2014 showing an increase in hotspot activities in southern Sumatra due to drier weather conditions.

Fig. 2D: NOAA-18 satellite picture on 27 August 2014 showing smoke haze emanating from scattered hotspots over western and southern Borneo.

Fig. 2E: NOAA-18 satellite picture on 30 August 2014 showing isolated hotspots with localised smoke plumes in central Kalimantan.

2.3 The hotspot charts for August 2014 for

Cambodia, Myanmar, Thailand, Lao PDR and Vietnam;
Sumatra, Borneo and Peninsular Malaysia;

are shown in Figs. 2F to 2G respectively

Fig. 2F: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam, Myanmar for August 2014.

Fig 2G: Hotspot Counts in Sumatra, Borneo and Peninsular Malaysia for August 2014.

3. Status of El Niño/La Niña

3.1 Following the slight easing of the tropical Pacific Ocean warming during the month of July, especially over the Niño3.4 region, August has seen temperature anomalies gradually increasing again. Expert assessment and most climate models predict this warming to continue, and that El Niño of weak strength is likely to develop in the last quarter of 2014. There is now about 60% chance of El Niño occurring in September-October-November season and this is down from 70-80% stated in June’s and July’s predictions.

3.2 Despite the observed warming over the tropical Pacific Ocean over the last few months, a number of atmospheric indicators of the El Niño, such as wind flow and cloudiness, have remained largely neutral. A plausible explanation for the lack of atmospheric response is that the warming has occurred over almost the entire tropical Pacific Ocean, including the sea areas in our region. During a typical El Niño development, warming is observed mostly in the eastern and central parts of the tropical Pacific Ocean.

3.3 With the forecast of a weak El Niño in the last quarter of the year, it should be noted that the El Niño is known to have relatively less impact on weather patterns in Singapore and the nearby region during the Northeast Monsoon season (typically from late November to March). The risk of drier weather conditions due to the El Niño is thus expected to be lower towards the end of the year.

3.4 Typically the impact from El Niño for the Southeast Asia region is drier than average rainfall conditions, especially for the southern and eastern parts (Figure E). More locally-specific impact differs from place to place and for different seasons. As the Southwest Monsoon season continues to prevail in the region, and with the possibility of a weak El Niño developing in the last quarter of 2014, the risks of occasional extended periods of drier and warmer conditions cannot yet be ruled out.

August 19, 2014

Review of Regional Weather and Smoke Haze for Jul 2014

Print Version

1. Review of Regional Weather Conditions in July 2014

1.1 Southwest Monsoon conditions continued to prevail in July 2014 with low level winds over the region blowing mostly from the southeast or southwest. Rain bands from tropical cyclones during the first half of the month led to extensive rain clouds over most parts of the ASEAN region. However, the northward migration of the monsoon rain belt accompanied with an intensification of typhoon activities in the Western Pacific Ocean and South China Sea during the second half of the month brought dry weather conditions over the southern ASEAN region.

1.2 he western Pacific Ocean and northern South China Sea experienced 4 tropical cyclones in July 2014, namely Typhoon “Neoguri”, Typhoon “Rammasun”, Typhoon “Matmo” and Severe Tropical Storm “Nakri”. On 10 July 2014, Typhoon “Rammasun” developed to the southeast of the Mariana islands, tracked westwards and made landfall over Luzon island, the Philippines. “Rammasun” intensified as it entered into the South China Sea before making landfall over Hainan Island and moving across northern Vietnam on 18 and 19 July 2014 respectively. Typhoon “Rammasun” resulted in widespread damage, killing at least 200 people and injuring hundreds more.

1.3 During the month, many parts of the Mekong Sub-region received more than 125% of normal rainfall due to the presence of the monsoon rain belt in the northern hemisphere. In contrast, most parts of the southern ASEAN region received less than 100% of normal rainfall with the exception of central Sumatra and western Java where more than 125% of normal rainfall was received. The regional rainfall pattern for July 2014 is shown in Figure 1A.

Fig. 1A: Percentage of Normal Rainfall for July 2014. The rainfall data may be less representative for areas with low density of rainfall network.

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

2.1 The prevailing rainy season continued to help keep hotspot activities subdued in the northern ASEAN region. Few to scattered sporadic hotspots were detected mostly in Myanmar and Vietnam during brief periods of drier weather.
2.2 Wet weather conditions during the first half of the month helped to subdue hotspot activities in the southern ASEAN region. However, a period of drier weather conditions led to an increase in hotspot activities mainly over Borneo and the northern half of Sumatra during the second half of the month. Scattered hotspots with localized smoke plumes were detected over the northern half of Sumatra between 18 and 29 July 2014. During this period, some areas along the western coast of Peninsular Malaysia reported unhealthy levels of Air Pollutant Index (API) between 100 and 200. Port Klang had the highest API of 139 on 21 July 2014. Similarly, scattered hotspots with moderate smoke haze were also detected mainly in western Borneo. The smoke haze led to a drastic drop in air quality mainly in Sarawak with unhealthy readings recorded at Sibu, Samarahan and Sri Aman on 28 July 2014. The return of shower activities towards the end of the month helped to ease the smoke haze situation in the region. Satellite images depicting some of the hotspot activities over the ASEAN region in July 2014 are shown in Figs. 2A to 2E.

Fig. 2A: NOAA-18 satellite picture on 18 July 2014 showing slight to moderate haze from some of the hotspots in central Sumatra.

Fig. 2B: NOAA-18 satellite picture on 20 July 2014 showing smoke haze from Riau affecting parts of the Strait of Malacca and western Peninsular Malaysia.

Figure 2C: NOAA-18 satellite picture on 21 July 2014 showing moderate smoke haze over Riau spreading across the Strait of Malacca to affect the west coastal states of Peninsular Malaysia.

Fig. 2E: NOAA-18 satellite picture on 26 July 2014 showing moderate smoke haze emanating from hotspots in West Kalimantan.

Fig. 2D: NOAA-18 satellite picture on 24 July 2014 showing scattered hotspots with localised smoke haze over western Kalimantan .

2.3 The hotspot charts for July 2014 for

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

are shown in Figs. 2F to 2H respectively

Fig. 2E: NOAA-18 satellite picture on 26 July 2014 showing moderate smoke haze emanating from hotspots in West Kalimantan.

Fig. 2F: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam, Myanmar for July 2014.

Fig 2G: Hotspot Counts in Java, Sulawesi, Philippines for July 2014.

3. Status of El Niño/La Niña

3.1 The tropical Pacific Ocean surface temperatures have continued to warm but gradually eased in recent weeks, slowing down the development of El Niño conditions. However, with most global climate models forecasting the continued warming of the tropical Pacific Ocean in the coming months, a weak to moderate El Niño is still likely to develop in the last quarter of 2014 .

3.3 In the last few months the sea surface temperatures in our region have been warmer than normal, leading to increased convection and formation of rain clouds. This has contributed to the relatively wet weather conditions in Singapore and the surrounding region during the current Southwest Monsoon season.

3.4 With the forecast of a weak to moderate El Nino in the last quarter of the year, it should be noted that the El Niño is known to have relatively less impact on weather patterns in Singapore and the nearby region during the Northeast Monsoon season (typically from late November to March). The risk of drier weather conditions due to the El Niño is thus expected to be lower towards the end of the year.

3.5 Typically the impact from El Niño for the Southeast Asia region is drier than average rainfall conditions, especially for the southern and eastern parts. More locally-specific impact differs from place to place and for different seasons. As the Southwest Monsoon season continues to prevail in the region, and with the possibility of a weak to moderate El Niño, the risks of occasional extended periods of drier and warmer conditions cannot yet be ruled out.