Strong gusts of wind and overnight drizzles led to a slide of the mercury in Kolkata and the rest of south Bengal.
However, till late Sunday evening, uniform and widespread rain eluded the city.
The maximum temperature at the Alipore Met office, which serves as the official record for Kolkata, was 33.8 degrees on Sunday, the lowest in 20 days. Just four days ago, the reading in Alipore was close to 41 degrees.
“The maximum temperature settled below the average after several days. The district also witnessed similar conditions,” said a Met official.
Sporadic showers were reported from western districts of West Bengal such as Bankura and Purulia on Sunday evening.
Rain-bearing thunderclouds had formed over Jharkhand on Sunday afternoon and were on their way towards the Bengal coast, a Met official said.
In the afternoon, the Met office started issuing thunderstorm alerts in Bankura, Purulia, Paschim and Purba Bardhaman, and Hooghly, suggesting the movement of the clouds.
“Usually, the clouds take around four hours to reach Kolkata on their way to Bangladesh. They feed on the moisture in the atmosphere as they near the coast,” said G.K. Das, director, India Meteorological Department, Kolkata.
“A strong spell of thunderstorm is due in Kolkata. When it will happen depends on when the clouds reach the coast,” Das said.
The city, Das said, will be denied the thunderstorm only if the clouds take a detour and move to Bangladesh via Nadia and Murshidabad.
The start of April was rainy and the maximum temperature was 32.3 degrees Celsius on April 2.
Based on the climatological data collected from 1991 till 2020, the usual daily maximum temperature in late April is 35.4 degrees Celsius.
The heat-wave conditions began in south Bengal around April 12-13. The spell was marked by low moisture count, unusual in Kolkata during summer.
A change in the weather was first spotted on Friday when the sky was cloudy and the condition breezy.
On Saturday night, gusts of wind started blowing across the city a little after 10pm. Streaks of lightning lit up the night sky, followed by drizzles.
Parched by the brutal heatwave, many Kolkatans flocked to their balconies and terraces to make the most of the pleasant weather.
Their prayers for a formidable spell of rain were, however, not answered.
Between 8.30pm on Saturday and 8.30am on Sunday, the Met office recorded around 2mm of rain in Alipore.
“Rain was reported from several places. But it lacked intensity,” said an official of the Met department.
When the tall thunderclouds from Jharkhand reach the city, the rain is expected to be widespread, the official said.
“A trough of low pressure, from north Bengal to Chhattisgarh, and a cyclonic circulation over Madhya Pradesh are leading to significant moisture incursion from the Bay. The dry westerly winds that had been dominating the upper reaches of the atmosphere have been replaced by moisture-laden southerlies from the Bay,” said Das of India Meteorological Department.