The Meteorological Department warns that while rainfall will ease today and tomorrow, heavy showers will persist in parts of the North and Northeast, driven by the monsoon trough and moderate south-westerly winds over the Andaman Sea and the Gulf of Thailand.
From Wednesday to Saturday, heavy to very heavy rainfall is forecast across the lower North, Central and lower Northeast regions, particularly in the East. The strengthening south-westerly monsoon is likely to fuel flash floods and landslides in provinces such as Nakhon Nayok, Prachin Buri and Trat.
Tropical Storm Tapah, currently in the upper South China Sea, will not have direct impact on Thailand, the department said.
Bangkok and its surrounding provinces will also be affected, with thunderstorms forecast to hit 60-80% of areas daily, accompanied by heavy downpours in some locations.
In Phichit, however, the crisis has already struck. The province is grappling with severe flooding as surging waters from the Yom and Nan rivers, combined with mountain runoff, have inundated nine districts and affected more than 1,500 households.
Heavy inflows from neighbouring Sukhothai and Phitsanulok have swollen the Yom River, flooding Sam Ngam, Pho Prathap Chang, Bueng Na Rang and Pho Thale districts. In total, 31 tambon and 136 villages are under water.
Phichit governor Thaniya Naipinit has declared disaster zones and authorised emergency aid funds. "We are providing urgent relief to ensure people receive support without delay."