Average temperatures in Sri Lanka are in the high twenties on the coast and high teens in the hills. In typical tropical fashion, the monsoon rears its head in Sri Lanka every year. Despite the small size of the island, its patterns vary depending on your location. The south of Sri Lanka (think the beaches of Hikkaduwa and Marissa, the hill country where Ella and Adam's Peak are nestled, and Udawalwe Nartinal Park) experience rains from May to August, meaning hiking or wildlife spotting during this period might get a bit soggy. The best time to visit the south and west coast of the island is from January to April.
Further north, around Sigiriya, the Cultural Triangle, Trincomalee and Jaffna, it's dry and hot from May to September. It gets rainy in these parts from October to February. Confused yet? Yep, it took us a while to get our head around it too. The most important thing to remember is that Sri Lanka is an amazing travel experience at any time of year, and places are rarely completely off limits.