The Andaman coast has a pronounced wet season driven by the southwest monsoon. The dry season runs from November to April, with the peak months being December to February: sunny, lower humidity, and excellent sea conditions for island hopping. March and April are still good but temperatures rise sharply.
The wet season (May to October) brings heavy rain, particularly in August and September. The sea can be rough and some boat services to the islands are suspended during this period. However, prices drop considerably and the crowds thin out. Krabi Town itself is perfectly functional in the wet season — the rain usually comes in short afternoon bursts rather than all-day downpours.
The Friday and Saturday walking street market on the riverside is year-round and well worth timing your arrival around.