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.
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.
2.3 The hotspot charts for September 2014 for
- Cambodia, Myanmar, Thailand, Lao PDR and Vietnam;
- Sumatra, Borneo and Peninsular Malaysia;
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.