May is just gorgeous in Sri Lanka, in between both monsoons and also very quiet.
If you are heading to Yala National Park, February until June or July are great, as the water tables are low, and animals come out to exposed lakes to drink.
You can play with the monsoons in Sri Lanka. The stunning beaches of the northeast have their monsoon October to January meaning that the European summer months of July, August and September are perfect here. While the southwest is still prone to rainfall.
Even though the Cultural Triangle is in a drier region, it does still get hit by the monsoon in November and December.
If you want to see blue whales, the beginning of March is the best time. But for other species, head there October until April.
December through to early January is a very busy time in Sri Lanka. So, although you can find quiet spots off the beaten track, you do need to book well in advance.