May in Battaramulla South, Sri Lanka, brings average daily highs of 31°C and overnight lows of 26°C in the 2016–2025 historical record. Allow room to shorten long outdoor plans when the day's forecast is hotter than you want. A schedule with easy breaks and less travelling between stops will give you more choices.
In the record, at least 1 mm of rain or snow falls on 29 of 31 days on average, a daily chance of 95%. Make flexibility part of the trip from the outset. Keep time outside easy to rearrange and choose plans that still work if it rains. The monthly figures do not establish whether rain is brief, prolonged or concentrated at a particular time.
The calculated day length, sunrise to sunset, averages about 12 hours. Sunshine averages 9 hours a day. Use the daylight window to plan the length of excursions, and check local sunrise and sunset times for the dates of your stay. Sunshine is a separate measure, and those hours need not arrive in one uninterrupted stretch.
For nature trips or walks, keep the longest outings movable and check route conditions locally; a monthly climate average cannot establish whether a particular path is accessible.
June has an average daily high of 30°C, 1°C lower than May. Its historical rain-day chance is 97%, compared with 95% this month. If your dates are flexible, compare those trade-offs with the kind of days you want. Neither set of averages predicts the conditions of one particular holiday.