Category Archives: Fortnightly Weather Review

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

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

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

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

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

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

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

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

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

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

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

1.1    The monsoon trough has migrated to the northern ASEAN region, with its position hovered mainly along the 10 N latitude line. The monsoon trough brought persistent shower activities over most parts of northern ASEAN.

1.2    Southwest Monsoon conditions, characterised by low level winds predominantly from the southeast or southwest, onset in the southern ASEAN region from the second half of June 2015. Wet weather conditions prevailed over the region in the first half of June 2015 and transited gradually to drier weather conditions with the onset of the traditional dry Southwest Monsoon season.

1.3    The rainfall over the southern ASEAN region in June has been lower than usual, which can partly be attributed to the prevailing moderate El Niño conditions in the equatorial Pacific Ocean which are likely to further develop in the months ahead. Sumatra, Java and southern Kalimantan received less than 50-75% of the normal rainfall; this is a typical precipitation pattern observed in southern ASEAN during a moderate to strong El Niño event. For the northern ASEAN region, below-normal rainfall has also been recorded in most parts except for central Thailand. The regional rainfall distribution for June 2015 is shown in Fig. 1A.

2.1    In the northern ASEAN region, hotspot activities continued to be subdued by the prevailing wet weather conditions.

2.2    In the southern ASEAN region, increased hotspot activities were detected during the period of drier weather in the second half of June. Persistent hotspots were observed on several days mostly in the provinces of Riau and Jambi in Sumatra. Smoke plumes and moderate haze were seen emanating from these hotspots.

2.3    In June 2015, most parts of Kalimantan were affected by showers. In the second half of June 2015, a period of drier weather led to the occurrence of isolated hotspots with localized smoke plumes in parts of western Kalimantan. Satellite images depicting some of the hotspot activities over the ASEAN region in June 2015 are shown in Figs. 2A to 2E.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

2.3    The hotspot charts for March 2015 for

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

are shown in Figs. 2F to 2H respectively

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

1.1    Inter-Monsoon conditions prevailed over the region for most parts of November 2014 before giving way to Northeast Monsoon conditions in late November 2014. The generally light and variable low level winds strengthened to blow predominantly from the northeast or northwest with the onset of the Northeast Monsoon season.

1.2    In November 2014, two tropical cyclones – ‘Nuri’ and ‘Sinlaku’ affected the equatorial region. ‘Nuri’ developed to the east-southeast of Guam in late October 2014 and intensified into Super Typhoon strength in early November 2014 before weakening and dissipating over the north-eastern Pacific Ocean on 6 November 2014. Tropical Storm ‘Sinlaku’ developed off the east coast of the Philippines in late November 2014. It intensified as it track northwestwards across the Philippines, and into over the South China Sea before dissipating as it made landfall over the south central coast of Vietnam on 30 November. ’Sinlaku’ brought heavy rains and strong winds to areas along its path.

1.3    As the region transitioned from the Inter-Monsoon to the Northeast Monsoon season, increased rainfall was experienced in the southern ASEAN region. In the second half of November 2014, increased convective activity in the South China Sea brought heavy rainfall to the eastern coastal states of Peninsular Malaysia which led to floods in Kelantan and Terengganu. For the northern ASEAN region, there was a decrease in rainfall and drier and cooler conditions were experienced.

1.4    In November 2014, many parts of the southern ASEAN region such as Sumatra and Peninsular Malaysia received more than 100% of normal rainfall. Less than 75% of normal rainfall was received in most parts of the northern ASEAN region while southern Philippines received more than 125% of normal rainfall. The regional rainfall distribution for November 2014 is shown in Fig. 1A.

Fig. 1A: Percentage of Normal Rainfall for December 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

1.1    The Southwest Monsoon season continued to prevail in the first half of October 2014 and gradually transitioned to the Inter-Monsoon season in the second half of the month.

1.2    Two typhoons and one tropical storm affected the north-western Pacific Ocean in October 2014, namely Typhoon Phanfone, Typhoon Vongfong and Tropical Storm Nuri. Typhoon Phanfone, developed in the last week of September 2014 and made landfall over Honshu, Japan on 04 October 2014 resulting in seven deaths and more than 62 injured. Shortly after Typhoon Phanfone made landfall, the wrath of Typhoon Vongfong swept across the islands of Kyushu and Honshu, Japan on 13 and 14 October 2014 respectively, bringing strong winds and heavy rainfall to islands. In addition, Typhoon Vongfong led to the cancellation of a few hundred flights to and from Japan.

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    Generally wet conditions affected the southern ASEAN region during the month. Brief periods of drier weather condition were observed in parts of southern ASEAN region, in particular, in Java island, southern Kalimantan and southern Sumatra. Less than 75% of normal rainfall was received in southern parts of Kalimantan and Sumatra, Java Island and Sulawesi while more than 125% of normal rainfall was felt in northern Sumatra, Peninsular Malaysia and Sabah in East Malaysia. The regional rainfall distribution for October 2014 is shown in Fig. 1A.

Fig. 1A: Percentage of Normal Rainfall for October 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