Affected by the high pressure area from China continuously extended its ridge to cover upper Thailand almost the month and it was occasionally strengthen,the weather of December 2015 was cool in most areas of upper Thailand almost the month especially cold weather in several areas of the northern and northeastern parts during the middle month.Cold to very cold weather with frosts reported in some areas of mountainous areas and mountain tops.However mean monthly temperature of this December was anomalous warmth in all parts of the country in particular across the northern, northeastern and central parts where notable warmth exceeds 2.0 C above normal.
With the occasionally passage of the westerly trough associated with the prevailing northeast monsoon throughout the month and the active low pressure cell in the middle South China Sea moved to cover the lower southern part and the Gulf of Thailand on 23-24December, unseasonal rainfall occasionally occurred in some areas of upper Thailand mainly during early and late month while abundant rainfall occurred mainly along the east coast of southern part nearly the whole month.However, monthly rainfall was above normalin northern part 25.3 mm (309%),central part 12.5 mm (240%), eastern part13.3 mm (164%) and southern part (west coast) 1.3 mm (2%) while it was below normal in northeastern part 1.0 mm (29%) and southern part (east coast) 83.7 mm (35%).