TMD warns of three days of heavy rain and rough seas as upper Thailand turns colder

THURSDAY, DECEMBER 11, 2025

Thailand’s Met Department warns of heavy rain and 2-3m waves in the South and storms then cooler, windy conditions over upper Thailand from December 11-16.

The Meteorological Department has issued Weather Advisory No. 11, warning of unstable weather over upper Thailand and several days of heavy rain and rough seas in the South.

From December 11-13, the South will see increased rainfall with heavy rain in many areas of Prachuap Khiri Khan, Ranong, Phangnga, Krabi, Trang and Satun. Very heavy rain is expected in Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung, Songkhla, Pattani, Yala and Narathiwat.

The department said this is due to a low-pressure cell over the lower South China Sea moving across the tip of Vietnam, the Gulf of Thailand and southern Thailand.

From December 14-16, the lower South will continue to experience heavy rain in many areas, especially in Surat Thani, Nakhon Si Thammarat, Phatthalung, Songkhla, Pattani, Yala, Narathiwat, Krabi, Trang and Satun, as the north-easterly monsoon over the Gulf of Thailand and the South strengthens.

Winds and waves in the Gulf of Thailand and Andaman Sea will also intensify. Waves in the lower Gulf will reach 2-3 metres, rising to more than 3 metres in thundershowers. In the upper Gulf, waves will be around 2 metres. In the open sea of the Andaman, waves will be over 2 metres, and higher than 2 metres in stormy areas.

People are advised to beware of heavy to very heavy rain and accumulated rainfall, which may trigger flash floods and runoff, especially on mountain slopes, near waterways and in low-lying areas.

Mariners in the Gulf of Thailand and Andaman Sea should proceed with great caution and avoid sailing in areas with thunderstorms, while small boats in the lower Gulf are advised to remain ashore.

For upper Thailand, the department forecasts unsettled weather with isolated thunderstorms from December 11-13, as easterly winds bring moisture over the region. Afterwards, temperatures will drop by 2-4°C and it will turn cool to cold and windy.

This change is due to a fairly strong high-pressure system or cold air mass from China spreading over Thailand. The public is urged to take care of their health during the changing weather, while farmers should prepare measures to protect crops and reduce potential damage.