The climate of most of Thailand
is governed by three seasons: rainy
(roughly June to October), caused by the southwest monsoon dumping
moisture gathered from the Andaman Sea and the Gulf of Thailand; cool
(November to February); and hot (March to May). The rainy season is
the least predictable of the three, varying in length and intensity
from year to year, but usually it gathers force between June and
August, coming to a peak in September and October, when unpaved roads
are reduced to mud troughs and whole districts of Bangkok are flooded.
The cool season is the most pleasant time to visit, although
temperatures can still reach a broiling 30°C in the middle of the day.
In the hot season, when temperatures rise to 40°C, the best thing to
do is to hit the beach.
Within this scheme, slight variations are found from region to region.
The less humid north experiences the greatest range of temperatures:
at night in the cool season the thermometer occasionally approaches
zero on the higher slopes, and this region is often hotter than the
central plains between March and May. It's the northeast which gets
the very worst of the hot season, with clouds of dust gathering above
the parched fields, and humid air too. In southern Thailand,
temperatures are more consistent throughout the year, with less
variation the closer you get to the equator. The rainy season hits the
Andaman coast of the southern peninsula harder than anywhere else in
the country - heavy rainfall usually starts in May and persists at the
same level until October.
One area of the country, the Gulf coast of the southern peninsula,
lies outside this general pattern - because it faces east, this coast
and its offshore islands feel the effects of the northeast monsoon,
which brings rain between October and January. This area also suffers
less from the southwest monsoon, getting a relatively small amount of
rain between June and September.
Overall, the cool season is generally the best time to come to
Thailand: as well as having more manageable temperatures and less
rain, it offers waterfalls in full spate and the best of the upland
flowers in bloom. Bear in mind, however, that it's also the busiest
season, so forward planning is essential.