August is the second half of the east coast peak. There is nothing to separate it from July on the water: the south-west monsoon is still blowing offshore, the Indian Ocean is still producing, and the points from Pottuvil down to Peanut Farm are running day after day.
What is worth knowing is that this is when Arugam Bay is fullest, since it coincides with the European holidays and the town is small. If you can choose between July and August, choose on flights and accommodation rather than on the surf, because the surf will not tell them apart. The south coast is still shut. The water is at 28°C.
