Two weather systems are driving the ongoing spell of rain across Bengal.

Both systems — an east-west trough and a cyclonic circulation — remain active, and thunderstorms are likely over the next few days, the Met office said.

In south Bengal, the current wet spell will continue at least until Wednesday, said Met officials.

The city and neighbouring areas received light rain on Saturday evening. Mild gusts of wind preceded the showers. In some parts of the city and its fringes, the sky had turned ominously black around 5pm. But the rain that followed was light.

The Met office recorded around 5mm of rain in Alipore.

“An east-west trough runs from northeast Madhya Pradesh to Manipur across Chhattisgarh, Jharkhand, Bengal, Bangladesh and south Assam. A cyclonic circulation now lies over north Bangladesh and adjoining Gangetic Bengal. In view of favourable wind patterns and strong moisture incursion from the Bay of Bengal, thunderstorms and associated activities are very likely to continue over the districts of Bengal,” said a Met official.

Passengers on a van caught in the rain on JL Nehru Road

Calcutta got light rain on Friday night as well, following consecutive thunderstorms on the two previous nights. On Wednesday, Alipore got around 52mm of rain and on Thursday, around 32mm.

The wet spell has brought the day temperature down. On Saturday, the maximum temperature at Alipore was 32 degrees Celsius, 3.5 degrees below what is normal for early May.

The spread and intensity of the showers are likely to peak on Monday, the day of the Assembly election results.

“On that day, light to moderate rain/thundershower is likely at most places over all the districts of Bengal, accompanied by streaks of lightning and winds clocking 60kmph or more. In some areas of north Bengal, the rain is likely to be heavy, but the wind speeds will be higher in south Bengal,” said the Met official.