The longtail - a traditional coastal vessel - had just dropped off five tourists at a popular destination in Krabi when strong winds and waves flipped the boat soon after noon.
The daylight storm off Ao Nang and the nearby popular landmark of Thale Waerk followed heavy waves that caused overnight damage among 25 boats anchored off a beach on the nearby island of Phi Phi.
While conditions vary slightly between the Andaman tourist provinces of Phuket, Phang Nga and Krabi, the onset of the monsoon season produces sudden, intense squalls in all three provinces.
On Phuket, heavy rain is considered to be a possibility to fall tomorrow - and its predicted to grow more intense for Monday's long weekend public holiday.
In Phang Nga, similar conditions are likely to prevail. Already, small boats in Phang Nga have been warned not to venture out on Monday.
In Krabi, there's a 10 percent likelihood of heavy rain tomorrow, rising to 40 percent on Monday.
Tourists in the region are advised to make their own decisions about safety and postpone day trips if conditions seem not ideal.