The advisory, issued on July 3, and effective untill July 8 advises for small boats to stay ashore and all ships to "proceed with caution" during the period.
In addition to waves of 2-4 metres that are expected in the Andaman Sea, which covers six Thai provinces – Ranong, Phang Nga, Phuket, Krabi, Trang and Satun – waves of up to three metres are also expected throughout the Gulf of Thailand, which includes the provinces of Trat, Chanthaburi, Rayong, Chonburi, Samut Prakan, Samut Songkhram, Phetchaburi, Prachuab Khiri Khan, Chumphon (Koh Tao), Suratthani (Samui, Phang Ngan), Nakhon Si Thammarat, Phatthalung, Songkhla, Pattani and Narathiwat.
Yesterday, an Iranian tourist drowned in a 2-metre wave off Patong after ignoring Red Flags posted on the beach.
In addition to heightened waves off Phuket, thundershowers are expected to hit between 40-60 per cent of the area, with temperature highs between 32-34 degrees Celcius, and lows averaging 22-24 degrees.
Commuters are advised to proceed on the roads with extra caution.