The high pressure area covered the upper Thailand. During mid-period, the another high pressure area from China extended its ridge to cover upper Thailand and the South China Sea while warmer air existed over Thailand at that time. In addition, the westerly trough moved through the northern part throughout the period. These conditions caused decreasing in temperature and increasing in rainfall with thundershower in upper Thailand during the second half of the period. Rainfall was observed in southern part mainly along east coast.