It is rainy season in Phuket & the Andaman coast right now, and it runs May to November. The rain tends to come hard and short rather than all day, and it stays warm through it — so the thing to bring is a shell you can fold into a day bag, not a coat.
Going in May
The southwest monsoon lands directly on this coast: rain most days, the biggest surf of the year and red flags on the beaches, heaviest in September and October.
What this means for your bag
A packable rain shell
Not a winter coat — it stays warm through the rain. A light hooded shell that folds into its own pocket ends up in the day bag instead of the hotel room.
See the Weather Protection packQuick-dry fabrics
Cotton takes two days to dry in this air and starts to smell before it does. Synthetics and merino wash in a sink and are wearable by morning.
See the Summer Sun Kit packA dry bag or two
Phone, passport and camera in something sealed. A cheap roll-top bag also doubles as the wet-clothes bag on the way home.
See the Weather Protection packShoes that survive being soaked
Streets flood faster than they drain. Sandals or mesh trainers dry overnight; leather does not, and one wet pair means walking in wet shoes all week.
See the Active & Adventure pack
Build a packing plan around the season you are actually travelling in.