Ngao Waterfall National Park's chief Lt Rittikorn Noonloi said that Ranong authorities had given a warning of heavy rain, flash flood, landslides and strong wind in the area.
The eight national parks, which are spread over the provinces of Ranong and Chumphon, have been instructed to issue warnings to tourists visiting waterfalls.
Officials will be on hand to help tourists in case of emergency, Rittikorn said.