IMD said monsoon is likely to shift northwards gradually towards foothills of Himalayas from July 18.
The India Meteorological Department (IMD) Friday forecast heavy rains over north and northeast India and issued a red warning for West Bengal, Assam and Meghalaya from July 19-21.
It also issued a red warning for Arunachal Pradesh from 19-20 and orange alert for July 21.
The expected rains are further likely to worsen the flood situation in Assam, where more than 39.8 lakh people in 27 of the state's 33 districts were affected by the deluge as on Thursday, it said.
The total number of people losing their lives in this year's flood and landslides in the state has gone up to 102. While 76 people died in flood-related incidents, 26 were killed in landslides, a bulletin by the state government said.
An orange alert has also been issued from July 19-20 for Uttarakhand, Punjab, Delhi, Haryana, Uttar Pradesh and Bihar.
The IMD said monsoon is most likely to shift northwards gradually towards foothills of Himalayas from July 18.
In addition, convergence of moist southerly, south-westerly winds from Bay of Bengal over Northeast and adjoining East India and from Arabian Sea over northwest India at lower tropospheric levels very likely from July 18.
Due to this, rainfall distribution and intensity is very likely to increase over the northern and northeastern parts of the country from July 18 and 19 respectively.
Isolated heavy to very heavy falls is very likely over north India during July 18 - 20 and over northeast east India during July 18 -21.
Extremely heavy falls are also very likely over sub-Himalayan West Bengal, Sikkim, Assam and Meghalaya during July 19- 21 over Arunachal Pradesh during July 19 -20, the IMD said.
This may accentuate existing flood conditions and also lead to landslides in some areas of northeastern states and sub-Himalayan West Bengal and Sikkim, the statement said.
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