The warning comes as parts of Khon Kaen province have already been inundated by flash flooding. In some areas of Baan Pai district, the water level is reportedly as high as two meters and residents are being evacuated.
The Department said 80 percent of Bangkok and surrounding areas will experience rainfall and possible thunderstorms in the next 24 hours. Drivers are being told to be vigilant.
Northern provinces listed in the flood warning and heavy downpour forecast include Chiang Mai, Tak, Sukhothai, and Nan provinces. In the Northeastern region, Surin, Nakhon Ratchasima, Buriram, and Khon Kaen were listed.
Central provinces listed include Suphan Buri, Ratchaburi, and Nakhon Sawan.
In the South, Prachuab Khirikhan, the province of Hua Hin resort town, is listed along with other seaside areas such as Phuket, Krabi, and Trang.