The city experienced heavy rainfall from Tuesday night owing to twin cyclonic circulations. The intensity of the downpour will increase in the next 48 hours.

The Met department said Bihar was surrounded by the two circulations. These led to the downpour at most parts of the state, including Patna.

“The ongoing spell of heavy rains has been caused by two cyclonic circulations prevailing around the state — the first one is lying over north Bay of Bengal and another cyclonic circulation is lying over eastern Uttar Pradesh. Consequently, Jharkhand, Bengal and Bihar are between the two cyclonic circulations,” Ashish Sen, the director (radar), Indian Meteorological Department (IMD), Patna, said.

“The monsoon trough line is also lying at its normal position: eastern UP, Bihar, Jharkhand, Bengal and the Bay of Bengal. As a result, most areas in Bihar have received good rainfall in the past 24 hours,” he said.

The Met department has also claimed that the intensity of rainfall would increase in the next 48 hours.

The evening bulletin of the IMD, Delhi, on Wednesday stated that rainfall occurred at most places over Bihar and rain with thundershowers would occur at many places in the state till July 27.

Despite the ongoing spell of heavy showers, weathermen have raised concerns over the erratic distribution of rainfall across the state so far. The rain deficiency is pretty high in some districts.

Bihar has received 357mm of rainfall between June 1 and July 25 against the normal of 441mm, making for a deficiency of 19 per cent during this period.

Nineteen of the total 38 districts have received deficit rainfall. Of the 19, eight districts have recorded deficit rainfall of above 40 per cent. “The rainfall distribution across the state has been abnormally uneven so far. We are assessing the reasons behind such uneven distribution in June and July,” said Sen.

The south-west monsoon entered in the state on June 19 but there was a lull in its activity after an aggressive entry. The state received 47 per cent deficient rainfall in June.