A low-pressure area in the Bay of Bengal is likely to bring widespread rainfall to Bihar for a few days starting Sunday.

Met officials predict Bihar will receive 1-2 per cent surplus rainfall in August against the normal of 291mm. Over the last month, the deficiency has already come down from 24 per cent to 7 per cent. The showers will bring it down even further.

"A fresh low pressure area with an associated upper air cyclonic circulation extending up to the mid-troposphere has developed over the northwest Bay of Bengal off Odisha coast. This system is likely to bring rainfall first in Odisha and Bengal, followed by Jharkhand and Bihar," said Ashish Sen, director, Patna meteorological centre.

"Some places in southeast Bihar could get moderate showers on Saturday as well, while the entire state is expected to receive moderate to heavy rainfall from Sunday and Monday."

Eastern India is under the influence of two low-pressure systems now. The second was around the northwest Bay of Bengal on Tuesday, bringing widespread rainfall in Jharkhand on Tuesday. On Wednesday, it moved to north Chhattisgarh and its neighbouring areas.

Bihar's tryst with the monsoon this year has been better than in 2015. While the rainfall deficiency between June 1 and July 31 stood at around 7 per cent this year, the corresponding figure from 2015 was 31 per cent.

Recovery in the monsoon figures started from around July 20, when the trough line shifted to the foothill of the Himalayas.

"Though rainfall was evenly distributed across the state, western parts of the state received comparatively less rainfall. Overall, rainfall in July was four per cent more than normal," said Sen.

Monsoon officially arrived in Bihar on June 17 after a delay of seven days and reached Patna by June 19. As of Wednesday, 17 districts had received normal rainfall (+/-19 per cent), 16 districts had received deficient rainfall (-20 to -59 per cent) and only five districts had received surplus rainfall (+19 per cent and above).

While 24 districts have received below normal rainfall, a dozen districts in north Bihar - Purnea, Kishanganj, Araria, Darbhanga, Madhepura, Bhagalpur, Katihar, Saharsa, Supaul, Gopalganj, Muzaffarpur and West Champaran - face flood conditions.

According to records with the disaster management department, around 29 lakh people have been affected by the north Bihar flood, which was caused by a rise in water level in rivers coming from Nepal.

"There are many districts in north Bihar which have not even received normal rainfall but saw floods because of heavy rain in Nepal," Sen said.

There are 17 river streams in the Himalayan region that flow into Bihar from Nepal. Nepal received heavy rain for around 10 days from July 18, aggravating the flood threat in adjoining north Bihar districts and those along rivers coming from Nepal.