March to April is a calm period with low wind speeds over most parts of the country. The southwest monsoon originates in the Indian Ocean during the month of May, and as a result wind speed greater than 6 ms−1 can be found in the mountainous areas in the South and the upper parts of the Northeast. It continues to blow until the middle of October with the strongest winds being experienced in June and July. By October the monsoon changes from a southwesterly to a northeasterly wind direction. Higher wind speeds are reached in December which is clearly seen in the southern part of the country.
The yearly average map (Fig. 5) shows that the areas which have relatively higher wind energy potential are located mainly in mountain ranges in the South with the mean yearly wind speed in the range of 6–7 ms−1. This mean wind speed is the highest value found in the country. This is likely due to the fact that the South is a narrow peninsula and the southwest and northeast monsoons blow into these areas largely unobstructed as upwind fetch is over a sea surface. In addition, the slope of the local mountainous terrain also helps to accelerate wind speeds as a result of compression due to the Bernoulli Effect.
Wind resource maps produced by TrueWind Solution (2001) exhibit high wind speed patterns similar to ours in the mountainous areas to the south of Thailand as well as low wind speeds in the northern regions of the country. However, some details such as high wind speeds in the northern mountain peaks obtained from this study do not appear in the TrueWind Solution maps which show no variation of wind speed over the region.