Patna: The Patna Met department on Thursday forecast June 10-15 as the date for the onset of the southwest monsoon in Bihar.

The monsoon is expected to drench the northeast part of Bihar - Araria, Kishanganj, Purnea, Katihar and Supaul districts - first and then advance to other areas.

The monsoon is expected to remain active in the state till October 15. This time normal rainfall is expected to be 98 per cent, with 5 per cent of deviation.

"The southwest monsoon will arrive in Bihar by normal date. It will arrive in the state between June 10 and June 15," said Anand Shankar, senior scientist at the Patna Met department. "Weather conditions in Bihar are favourable for the onset of monsoon. The pre-monsoon showers being witnessed for the last few days are indication of arrival of the southwest monsoon on time."

The Met department has also forecast cloudy skies with possibility of development of thunderstorm or dust storm and lightning in Patna till June 5.

Shankar attributed this to the moisture coming from Bay of Bengal. A cyclonic circulation is forming there which will strengthen in coming days and this will only bring monsoon in Bihar by June 15, he said. The southwest monsoon enters India's land area in two wings. The eastern wing hits the Andaman and advances towards the northeast and eastern parts of the country, while the southern wing hits Kerala. Though the southwest monsoon is usually expected to reach the Kerala coast by June 1, this year it arrived on May 29.

The all-India weather bulletin issued by the Delhi headquarters of the India Meteorological Department (IMD) on Thursday said that a trough running 0.9 km above mean sea level will bring scattered rain for the time being over parts of Bihar and Bengal, and isolated showers are expected over Jharkhand and Odisha also. Isolated showers over Gangetic East Bihar, Bengal, East Jharkhand and Odisha may also occur, a weatherman said.