Summer storms are forecast for the Northeast from Sunday, moving to other areas including Greater Bangkok during the week.
The Meteorological Department warned on Friday that turbulent conditions - thunderstorms, gusty winds and some hail - were expected from Sunday to Tuesday in northeastern provinces.
The storms would slowly move into the northern, eastern and central regions. Bangkok and its vicinity could expect three days of storms.
The first storms of the summer season are being caused by a high-pressure area coming from China meeting with high temperatures in the kingdom, the department said.
Upper Thailand officially entered summer on Wednesday with a change in the prevailing wind.
The Royal Irrigation Department said on Thursday it had prepared for flooding during the storms.
The heavy rain forecast for next week comes after moonsoon downpours pounded the southern region last week, causing flooding in all provinces along the Gulf of Thailand.
The Disaster Prevention and Mitigation Department said on Friday that Pattani was the only province still flooded - in Muang, Mai Kaen, Nong Chik and Sai Buri districts - but water levels were receding.