Cambodia has a tropical climate with three different seasons. It's
recommended to visit the country during the dry period, November to
March, when the temperatures are cooler and the weather is more
pleasurable. The monsoon season is also a good time to visit as the country is green, the rivers and lakes full and the rains are entertaining.
There is inevitably a hot season from March to June and,
due to the tropical climate there is rainy period from May to the end
Phnom Penh experiences a mild monsoon season with the rain usually being predicatable and only lasting for a short period of time.
For comparison with the other big city, Siem Reap is
definitely cooler than the capital. Sihaounkville being on the coast receives more than it's fair share of the rain in the monsoon season, sometimes it rains for weeks on end.