Parts of Sukhothai province, already under one metre of water from recent heavy rain, can expect a further deluge from upstream, but authorities believe the Chao Phraya River basin will be safe.
The heaviest flooding took place in parts of Khiri Mat district on Saturday, including tambons Nong Chik, Sri Khiri Mat and Thung Luang. About 700 houses were inundated and isolated as a result. Rescue workers had to evacuate residents and pets on boats.
Officials have been mobilised to provide help as more runoff from Phran Kratai district of Kamphaeng Phet was starting to arrive. However, central areas and historical parks of Sukhothai remained safe on Saturday.
The Meteorological Department predicted that rain would ease in upper Thailand over the weekend but would increase from Monday to Friday.
Thongplew Kongjun, deputy director-general of the Royal Irrigation Department, said floodwater from the North would not threaten the Chao Phraya basin because the reservoirs of major dams were still at less than half of their capacities and soil was dry.
The flooding in the early rainy season that has happened in upstream areas would be short-lived because it resulted only from runoffs, he said. He assured that the severe flooding seen in 2011 would not recur this year.
The department intends to store large volumes of rainwater in the early rainy season in major dams so that there will be enough for later use as rain is expected to be lighter in June and July.
Mr Thongplew said the heaviest storms would arrive from August to October.