The Alipore Meteorological Office on Thursday issued a thunderstorm and rain alert for three districts of South Bengal, including Kolkata. In a special bulletin issued in the afternoon, a red alert was issued for Howrah. Kolkata and South 24 Parganas, meanwhile, have been placed under an orange alert. These districts may experience heavy rain accompanied by thunderstorms and gusty winds.

Kolkata and its suburbs witnessed bright sunshine since morning. However, as the day progressed, the sky turned dark. A brief spell of rain left several roads across the city waterlogged.

Water accumulated in Salt Lake Sector V, including in front of the Electronics Complex Police Station, causing disruptions to traffic.

The weather office said North 24 Parganas, East Midnapore, West Midnapore, Jhargram, Purulia, Bankura, Murshidabad and Nadia have also been placed under an orange alert on Thursday.

These districts may receive thunderstorms and rain, accompanied by gusty winds reaching 30 to 40 kmph. Scattered rain will continue in other districts of South Bengal.

Kolkata and the rest of South Bengal are likely to witness scattered rainfall every day until Sunday, with a yellow alert in place.

In North Bengal, isolated spells of heavy rain are expected. Darjeeling, Jalpaiguri, Kalimpong and Alipurduar may receive heavy rainfall on Thursday and Friday. Other districts are also likely to witness scattered rain, lightning and gusty winds over the next two days. Rainfall is expected to decrease in North Bengal from Saturday.

Meanwhile, preparations for the withdrawal of the monsoon have begun in western India. The Alipore weather office said the southwest monsoon may withdraw from some parts of western Rajasthan by September 19.

The monsoon trough is currently extending through Saurashtra and a low-pressure area near the northeast Arabian Sea.

It then passes through Rajasthan, Haryana, Uttar Pradesh and Jharkhand before entering West Bengal and extending over the Bay of Bengal via Digha.

A cyclonic circulation over northern Thailand may move into the North Andaman Sea by Friday evening. Under its influence, a low-pressure area may develop over the region.

It is likely to gradually move north-northwestwards and reach the Odisha-Andhra Pradesh coast within three to four days.

In addition, a trough extends from North Bengal to northern Odisha. Under its influence, conditions remain favourable for thunderstorms and rainfall across West Bengal.