May in Khlong Sam Wa, Thailand, brings average daily highs of 34°C and overnight lows of 27°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 21 of 31 days on average, a daily chance of 68%. 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 13 hours. Sunshine averages 10 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.
Start with the places you most want to visit, then keep the order flexible enough to suit the weather. Check current opening hours and local transport before fixing long day trips. The climate record can help with pacing and packing, but it does not describe what is open during your stay.
The following month, June, has a similar average daily high of 34°C. Its historical rain-day chance is 69%, compared with 68% 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.