Climate
Thailand locates in humid tropical region and remains moderately warm for the whole year. Average temperature all over Thailand is 29c ranging in Bangkok from 35c in April to 17c in December. There are three seasons in northern, northeastern, central, and eastern Thailand and two in southern Thailand. The cool season (November to February), the hot season (March to May), and the rainy season (June to October), though downpours very seldom last more than a couple of hours.

Phuket's weather conditions are dominated by monsoon winds that blow year round. It is therefore always warm and humid. There are two distinct seasons, rainy and dry.
The rainy season begins in May and lasts till October, during which the monsoon blows from the southwest.
The dry season is from November through April, when the monsoon comes from the northeast.
Highest average temperatures, at 33.4ºC, prevail during March. Lowest averages occur in January, when nightly lows dip to 22ºC.

Phuket has a tropical monsoon climate. It's warm all year 'round, but the two periods of April-May and September-October are the hottest. The September-October period is also the wettest.
The best time to visit Phuket is during the cool NE monsoon season, from November though March, when it isn't so humid, and the cool breezes keep things comfortable. The average temperature is around 75ºF to 89ºF (24ºC to 32ºC).

The hottest time is from April through May, with temperatures ranging from 80ºF to 95ºF (27ºC to 36ºC). There are frequent short heavy thundery showers, offering welcome relief from the temperature and humidity. The Thai New Year occurs on April 13th and everyone sprinkles (or throws) cool water on each other. No wonder!

Locals enjoy June, July and August, since the weather is usually fine and our favourite haunts remain uncrowded. The usual pattern is brief but heavy showers, with plenty of sunshine between downpours. Everything is a little less expensive at this time of year, as well. Temperatures range between 70ºF and 90ºF (20ºC to 33ºC).

During September and early October locals start to remember their umbrellas. This makes an ideal time to visit abroad. One consolation for those who remain is that the beaches, outdoor restaurants and streets are relatively uncluttered by visitors.

And even at this time, we still get long intervals of sunshine between the heavy showers. Plenty of low season activities, both water- and land-based, are still available on Phuket during this wettest part of the summer season.

What to Wear
For the Western visitor there is no such thing as "cool". Just cooler than "hot" and "drier than humid", so light cotton clothing is the order of the day. Don't worry about bringing too much clothing with you, as almost everything can be purchased locally, at a fraction of the price you will pay at home. Do remember that the tropical sun can be quite fierce so a hat is useful, and don't forget to use a good sun screen.