Bangkok Post

The last time such a severe storm headed Thailand's way was in 2009, when tropical storm Ketsana ravaged many areas of the North, Northeast and the Central Plain.

"Gaemi is the same magnitude as Ketsana," Somchai Baimuang, deputy director-general of the Meteorlogical Department said.

Ketsana caused havoc in 36 provinces, affecting 1.8 million people, in late September-early October 2009.

Gaemi will enter Vietnam on Friday morning. It is expected to lose strength as it moves overland  across Cambodia into Isan, but will still be dangerous. Reports say it will likely enter Thailand about 8pm on Friday.

Weather experts predict Tropical storm Gaemi will become more circular in shape as it gains strength and moves west towards Vietnam. Photo from wunderground.com

Mr Somchai warned there could be serious damage in areas which take the brunt of the storm. 

The lower northeast will be directly hit by the storm late Friday and over the weekend as Gaemi moves westward and then finally out of the country on Monday. Other provinces in the lower part of the northern region, Central Plain, Bangkok and southern provinces will also be affected by the storm.

"People in the risk areas should beware there could be severe weather during this period," the department's warning said.

As of 4pm on Wednesday Bangkok time, Gaemi was 950 kilometres off the coast of Da Nang, Vietnam, and moving westward.

With Gaemi looming,  the government and Bangkok Metropolitan Administration are draining water from dams and canals in preparation for the worst.

City Hall expects rain in 80% of the capital and Bangkok Governor MR Sukhumbhand Paritabra has ordered officials to keep a close watch on the water levels in all canals.

City Hall is pumping water out to the Chao Phraya River and the Royal Irrigation Department insists that its reservoirs and dams can cope with the expected heavy rain.