Weather in Siem Reap in May

The month to avoid. May is the month most people should skip in Siem Reap. You should expect rain on 22 days of the month, which is more days wet than dry.

May ranks 12 of 12 — near the bottom of Siem Reap's year. December is the month that works, and the swing between the two is 39 points, which is a different holiday rather than a slightly better one.

Rain on 22 of the month's 31 days, 4 of them heavy. At that frequency a wet-weather backup is not a contingency, it is the itinerary — book the indoor things first and treat the clear days as the bonus. Pack for heat management rather than style: shade, water, and a schedule that gives up on the middle of the day.

What the averages hide

Averages flatten a month, and this one hides a few things: 11 days clear 35 °C, so a serious heatwave is normal rather than notable. Across the twenty years measured, the hottest May day reached 41.2 °C and the coldest night fell to 22.1 °C, and the wettest single day dropped 38 mm — roughly 27% of the month's rain in one day.

May is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest May on record still delivered 265 mm against 46 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 140 mm average is a reasonable planning figure, not a promise.

Wind is light at 5.3 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 75%, high enough to notice on the warm days without dominating them.

How May sits in the year

The month is on the way down: 1.9 °C cooler than April, with June dropping another 2.1 °C. The first week and the last are not the same trip. Rain has already shifted: 9 days more than April had.

Daylight in May

Siem Reap sits close enough to the equator that daylight barely moves all year — 12.7 hours in May, against a range of just 1.6 hours across the whole calendar. Sunrise and sunset land at roughly the same time whenever you come.

An inland climate

Despite being inland, the year stays fairly even: 16.1 °C between the year's warmest afternoons and coldest nights.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

May in Siem Reap versus nearby

If Siem Reap is one option among several, the nearby comparison is worth making. Ubon Ratchathani is close enough to be a coin toss — within a degree on temperature, 1 day less rain. Nakhon Ratchasima is close enough to be a coin toss — within a degree on temperature, 2 days less rain.

So: May is a compromise. December is 39 points better and is what Siem Reap is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Siem Reap

See all twelve months in Siem Reap, or where else to go in May.