Cambodia has a tropical monsoon climate with three distinct seasons that dominate daily life and agriculture: a hot dry season, a wet monsoon season and a cool dry season. The country sits in the heart of mainland Southeast Asia and is dominated by the Mekong River and the Tonle Sap lake, the largest freshwater lake in Southeast Asia, whose water level rises and falls dramatically with the monsoon cycle.
Climate
Cambodia's climate is governed by the Southwest and Northeast monsoons. The country is generally flat and low-lying, which gives temperatures a relatively uniform distribution — it is hot nearly everywhere nearly all the time. Average annual rainfall ranges from about 1,400 mm in the central plains to over 5,000 mm on the Cardamom Mountains in the southwest.
The Tonle Sap flood cycle is one of the most remarkable climate-driven phenomena in Southeast Asia. During the dry season the lake covers about 2,500 km² with an average depth of just 1 metre. When the monsoon arrives, the Mekong River swells so much that its flow actually reverses and pushes water back up the Tonle Sap River into the lake, expanding it to over 10,000 km² and making it the largest lake in the region. This flood pulse supports one of the world's most productive inland fisheries.
Cambodia is outside the main typhoon track but can be affected by the remnants of tropical storms that have crossed Vietnam. Flooding along the Mekong is a recurring concern during peak monsoon months, especially for communities in the provinces of Kandal, Prey Veng and Kampong Cham.
Seasons
Cool dry (November – February)
The most comfortable time of year. Temperatures drop slightly — Phnom Penh averages 27°C during the day and 21°C at night, Siem Reap can drop to 18°C overnight. Skies are mostly clear and humidity is lower than at other times. This is peak tourist season for Angkor Wat.
Hot dry (March – April)
The hottest months. Daytime temperatures regularly reach 36–38°C in Phnom Penh and Siem Reap, sometimes exceeding 40°C. Humidity rises through April as the monsoon approaches. The countryside is dry and dusty. The Khmer New Year (mid-April) falls during the hottest week of the year.
Rainy / monsoon (May – October)
The southwest monsoon brings daily rainfall, usually in the form of dramatic afternoon thunderstorms. Mornings are often clear and sunny. Rainfall peaks in September and October, which are also the months when the Tonle Sap reaches its maximum extent. The landscape turns a vivid green and rice paddies are at their most photogenic.
End of monsoon (October – November)
Rainfall tapers off through October as the monsoon retreats. The Tonle Sap is at its highest water level. The annual Water Festival in Phnom Penh celebrates this moment when the Tonle Sap River starts flowing back toward the Mekong. Nights become cooler and humidity drops through November.
Extreme weather events
Cambodia's most frequent weather disasters are monsoon floods along the Mekong and Tonle Sap. The 2000 and 2011 floods were among the worst in living memory, displacing hundreds of thousands and causing extensive damage to rice crops. Drought during El Niño years (2015, 2019) has also severely affected agricultural production. Unlike its eastern neighbour Vietnam, Cambodia rarely experiences direct typhoon landfalls, though storm remnants regularly cross from Vietnam and add to monsoon rainfall totals.
Regional variation
The central plains around Phnom Penh, Battambang and Kampong Cham are hot, flat and heavily agricultural. These areas are most exposed to Mekong flooding.
Siem Reap (the gateway to Angkor Wat) sits in the central plain and has a similar climate to Phnom Penh but with slightly cooler nights during the dry season.
The southern coast around Sihanoukville and Kep is wetter and more humid than the interior, with a stronger maritime influence. Rainfall here can exceed 3,500 mm per year.
The Cardamom Mountains in the southwest are the wettest part of the country, receiving over 5,000 mm of annual rainfall on the windward slopes.
Best time to visit
The best time to visit Cambodia is November to February during the cool dry season. Skies are clear, temperatures are manageable and the monsoon rains have passed. This is peak tourist season for Angkor Wat. December and January are ideal. Avoid March to May if you're sensitive to heat — it is genuinely uncomfortably hot. If you want to see the Tonle Sap at its fullest, visit in late September or October, just after the peak of the monsoon.
Climate facts
- The Tonle Sap is the only river in the world that changes direction twice a year — pushed upstream by monsoon flooding then reversing as the floodwater drains out.
- The Khmer New Year is deliberately celebrated in mid-April during the hottest week of the year, a tradition that pre-dates modern calendars.
- Cambodia's dry season can be so extreme that river levels in the Mekong drop enough to expose long stretches of sandbanks that are underwater for half the year.
- The Cardamom Mountains contain some of the last large blocks of intact lowland rainforest in Southeast Asia, preserved partly by their inaccessibility and very high rainfall.