Review of Regional Weather and Smoke Haze for Aug 2014
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.
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.
2.3 The hotspot charts for August 2014 for
- Cambodia, Myanmar, Thailand, Lao PDR and Vietnam;
- Sumatra, Borneo and Peninsular Malaysia;
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.