Thai local media reported the phenomenon, with images showing the waterspout clearly visible off Koh Racha Yai in Rawai.
Several tourist and passenger boats were seen in the vicinity, although there were no reports of injuries or damage.
The waterspout gradually dissipated after forming over the sea. While such phenomena are usually short-lived, they can pose a risk to vessels in their path, particularly during thunderstorms and periods of strong winds.
The TMD warned that the southwest monsoon over the upper Andaman Sea would strengthen from July 27-30, with waves forecast to reach two to three metres.
The TMD advised boats to proceed with caution, avoid areas experiencing thunderstorms, and for small boats in the upper Andaman Sea to remain ashore during the period.