The flood-risk provinces identified by the office are Amnat Charoen, Yasothon, Si Sa Ket, Ubon Ratchathani and Mukdahan in the Northeast, and Sa Kaeo, Chanthaburi and Trat in the eastern region. Rain will cover Ranong, Satun, Krabi and Trang in the South.
Supoj Tovichakchaikul, the agency chief, said governors of the provinces have been ordered to stay alert for possible flooding. Deputy Interior Minister Chuchart Hansawat has also directed governors in another 18 provinces to prepare for possible heavy rain, flash flooding and forest run-off.
Prime Minister Yingluck Shinawatra has directed the Disaster Prevention and Mitigation Department to ensure that provincial officials are ready to provide assistance where ever needed.
The Meteorological Department warned of heavy rain and wind until Monday after Gaemi reached Vietnam and spilled its impact to Cambodia and Thailand.
The storm will "cause torrential rain with heavy to very heavy rain in many areas and windy over the Northeast and the East for the first place following the Central and the lower North from Oct 6 to 8. People in the risk areas should beware of the severe weather," it said.
Deputy chief of the weather bureau Somchai Baimuang said people should just stay calm as the storm moves towards Thailand and go about their normal life.
His comment was at odds with Science and Technology Minister Plodprasop Suraswadi, who heads the government's Water and Flood Management Committee. Mr Plodprasop asked people to stay home unless they really need to go out during the storm. and leave the streets free for work crews combatting any flooding.
The science minister on Friday said his message was routine practice in Western countries and was intended to ensure public safety and give relief crews freedom to work without disruption.
"I believe the impact of tropical storm Gaemi on Thailand will be less severe than some have predicted, because it will likely weaken to a tropical depression once it enters the country," Mr Plodprasop said.
"Gaemi's windspeed should be reduced from 90 kilometres per hour to 30 kilometres per hour when it reaches Thailand. A tropical storm is strong when it is over the sea. Gaemi should lose its strength when it makes landfall."
the National Water and Flood Management Policy Committee now says the storm will enter Vietnam, Cambodia and Laos on Saturday and move into Thailand on Monday.