Most people will say that the best month to visit Phang Nga is January, as it’s warm and mostly dry throughout the month. Maximum temperatures will be around 30 degrees C with overnight minimums about 23-24. It’s the coolest month of the year in Thailand. Most beaches will be open and safe for swimming and there will still be some water in the waterfalls (at least until the middle of the month).
However, January is the height of the tourist season, so there will be lots of people wherever you go (although far less crowded than nearby Phuket).
February is a good option too because it is as dry as January, but temperatures will start rising towards the end of the month.
March and April are the hottest months with temperatures rising to around 34 degrees C and overnight minimums about 26-27. Historical records show that rainfall in March and April should be higher than January and February, but in recent times there have several years where there has been almost no rainfall in March and April, so these two months can be somewhat unpredictable (perhaps because of climate change).
If you don’t like the heat, then March and April are not the best months for you.
May sees the start of the southwest monsoon and it can be very wet for a couple of weeks (but cooler than March/April). From this point on (through to the end of the rainy season) the Andaman coast beaches are not safe for swimming because of strong rips.
The rain then eases off a little through June, July and August and for many people this is a pleasant time of the year as temperatures drop by a couple of degrees due to the predominantly cloudy skies. They are great months for enjoying Phang Nga’s many waterfalls. Rainfall is intermittent and is mainly afternoon or overnight thunderstorms interspersed with sunny periods.
If you like the ‘green season’ and don’t need to be here during the high season, then many will say that June is the best month to visit Phang Nga in the rainy season because June has fewer big storms and longer sunny periods.
September and October are the wettest months and there may be limitations on visiting Phang Nga’s many nature attractions because of minor flooding (Phang Nga generally does not experience the major flooding that occurs in Phuket and many other regions of the country). These are the only two months when you might experience 2-3 days of non-stop rain.
November sees the rain starting to ease off about halfway through the month as the northeast monsoon brings cooler air down from the Asian sub-continent, and December is a transition month into the dry season which is usually well under way by Christmas.
The northeast monsoon is not as strong as the southwest monsoon, and it is the east coast of Thailand that experiences most of the rain from the northeast monsoon. By the time it reaches the Andaman coast there is less moisture to produce rainfall over Phang Nga.
Given that some people like it hot, some like it dry, and some like the rain, it could be said that there is no one best month to visit Phang Nga – it depends on your personal wants and needs.