I went to SriLanka in August a few years ago and it was supposed to be at the tail end of the monsoon season.
Yes I'm afraid it did rain, nearly every day but the showers were short lived (although very, very heavy) then the sun would come out again and you'd carry on sunbathing. It was always hot, whether it rained, was cloudy or sunny, so the temperature wasn't affected by the rain.
We used to jump in the pool when it rained!
One day we decided to go for a long walk down the beach (about 2 miles and utterly deserted) when we set off it was bright blue sky, and after we'd walked a couple of miles the sky clouded over suddenly and the skys opened. We were in our swimming costumes and ran all the way back being pelted with rain, the wind was blowing a gale and driving the sand staight at us. For a few moments I didn't think we'd make it back (Yes I know very melodramatic!!)
But other than that we had a fantastic holiday and I'd really go back again, even in August.
I think the best time to go is around November.
Where are you going? We stayed at the Tritan Hotel at Ahungella. I'm not sure but I think all that side was destroyed by the tsunami, but I guess they will have repaired and rebuilt things by now.