Phuket's weather is almost the same as Krabi with average temperatures
around 75ºF to 89ºF (24ºC to 32ºC) year round. Phuket has some of the most constant temperatures of all the popular tourist destinations in Thailand. Highs and lows vary by only about five degrees farenheit over the course of the year.
The rainy season, which coincides with the European and North American summers, is not an entirely bad time to visit, since the rain generally falls within the span of an hour or two in the late afternoons. The rain cools down the temperatures a bit and cleans the air quite nicely. With the high temperatures, the rain is not exactly cold. Sometimes it can be like a warm shower.
The rainy season is generally shorter and more pronounced in Phuket than it is in Bangkok. The rain increases sharply in September, but then tapers off just as quickly. January and February are the best months to visit if you want to avoid just about any possibility of rain.