Overall the best time to visit the region is between November and April when it should be dry and not too hot. In the south it is warm with lovely cool evenings. However, in Cambodia wind-blown dust invades everything at this time of year. In the north of Vietnam and Laos the highlands will be a bit chilly but they should be dry with clear blue skies. Temperatures in upland areas like the Plain of Jars, the Bolaven Plateau and some towns in the north of Laos can be extraordinarily cold.
From late-March to April the region heats up and temperatures can exceed 40°C. In northern Laos, the months from March through to the first rains in May or June can be very hazy as smoke from burning off the secondary forest hangs in the air. On the worst days this can cause itchiness of the eyes. It also means that views are restricted and sometimes flights are cancelled. Travel on the region’s mud and laterite roads is difficult and sometimes impossible by June and July; transport will be slower and may cease altogether in some parts. It is also difficult to do any outdoor activities in June and July because of the rain. However, the area is at its most beautiful then. Travel in the south and Mekong Delta can be limited at the height of the monsoon (particularly during September, October and November). The central regions and north of Vietnam sometimes suffer tropical storms from May to November. Hue is at its wettest wet from September to January.
Tet, the Vietnamese New Year, is not really a good time to visit. This movable feast usually falls between late January and March and lasts for about a fortnight. It is the only holiday most Vietnamese get in the year so popular destinations are packed, roads are jammed, airlines booked and, for a couple of days, restaurants are shut and all hotel prices increase and car hire prices rise by 50% or more. Problems also occur during Khmer New Year in Cambodia and Pi Mai in Laos (both usually mid-April), when public transport is full and and hotels booked out in popular places.