1.1             Moderate Northeast Monsoon conditions prevailed over the region in December 2011, bringing dry and cool weather to parts of the Mekong Sub-region of Cambodia, Lao PDR, Myanmar, northern Thailand and Vietnam. In the southern ASEAN region, the Northeast Monsoon brought wet weather conditions to Brunei Darussalam, Indonesia, Malaysia, Singapore and southern Thailand.

1.2       Several episodes of monsoon surges affected the region during December 2011. Monsoon surges are typical of the Northeast Monsoon season and are characterised by the steady strengthening of moisture laden north-easterly winds over the South China Sea. The surges in December 2011 brought wet and windy conditions to parts of the southern ASEAN region. Continuous heavy thunderstorms over several provinces in southern Thailand at the end of the month led to widespread flooding and landslides in some places. On 13 December 2011, Tropical Storm Washi developed over the Pacific Ocean to the east of the Philippines. It made landfall over Mindanao and Palawan islands on 16 and 17 December 2011 respectively, resulting in many fatalities and the evacuation of people from their homes.

1.3       In December 2011, many parts of the northern ASEAN region such as Cambodia, Lao PDR, Myanmar and northern Thailand received less than 50% of normal rainfall. Philippines received more than 150% of normal rainfall likely due to the impact of Tropical Storm Washi. In the southern ASEAN region, most parts of Peninsular Malaysia, Borneo and Singapore received more than 100% of the normal rainfall while southern Sumatra and Java Island received less than 100% of normal rainfall. The regional rainfall pattern for December 2011 is shown in  Fig. 1.