India Meteorological Department's (IMD) Director-General Laxman Singh Rathore said a Monsoon trough will bring "heavy" to "very heavy rainfall" in the foothills of Himalayas.
"The rainfall will also lead to swelling of rivers Kosi, Gandak and Ghaghara, tributaries of Ganga and all tributaries of Brahmaputra.
"This will possibly lead to flooding of plains in East Uttar Pradesh, Bihar, Assam and sub-Himalayan parts of West Bengal," Rathore said, after a high-level meeting convened by the National Disaster Management Authority (NDMA).
He said the states which are likely to be affected have been asked to be in touch with the concerned agencies in case of any exigency.