Storms, Flooding and Weather Safety on Koh Samui

Summary

Serious tropical storms are not common on Koh Samui, but they do happen, almost always during the northeast monsoon (roughly October to early December). Past events include severe flooding in November 2011 and a storm in October 2017 that stopped ferries for over a week. Most monsoon seasons pass with only temporary disruption. The practical advice: in October-November, allow buffer days around flights and ferries, book accommodation you can cancel, and follow local weather warnings.

Safety tips

• In October-November, keep one flexible buffer day before any flight home.
• Book refundable rooms and tours in the monsoon peak.
• Do not swim when red flags are up or the sea is rough; rip currents can occur.
• Follow Thai Meteorological Department (TMD) forecasts and local advice during storm warnings.
• Low-lying parts of Chaweng and Nathon can flood after very heavy rain.

Jellyfish note

Box jellyfish, whose stings can be very dangerous, occur in Gulf of Thailand waters including Koh Samui, mainly in the rainy/calm-water periods (sources differ on exact months; estimates range from about October to April, and July-October has also been flagged). Main beaches such as Chaweng and Lamai have vinegar first-aid stations. If stung: flood the area with vinegar for at least 30 seconds, do not rub, do not use fresh water, remove tentacles carefully, and get medical help immediately (Thailand emergency medical line: 1669).